This edition of OilChat commemorates the fourth anniversary of our newsletter. In the very first issue we addressed the various types of Lubricating Base Oils. Base oils are of prime importance since they are the foundation of all lubricants. Considering the number of new visitors to our website and the amount of enquiries we receive regarding base oils, we have deemed it appropriate to revisit the topic, synthetic base oils in particular.

The American Petroleum Institute (API) categorizes hydrocarbon based oils into four main groups. The classifications are based on the refining method and the properties of base oil, including viscosity index (VI), saturates and sulphur content. Base oils that are not included in the first four groups are incorporated in a fifth group.

Group I is the least refined type and consists of conventional petroleum (mineral) base oils, normally produced by Solvent Refining i.e. a solvent extraction process to remove various undesirable compounds and impurities from the base oil. Group I base oils are straw to light brown in colour and typically have a VI somewhere around 100.

Group II represents a better grade of mineral base oil and is normally produced by Hydrocracking. One of the advantages of hydrocracking is its ability to remove most of the remaining unstable aromatic (unsaturated) hydrocarbons and sulphur. With the majority of the undesirable compounds removed they are more stable and have a much clearer colour. Group II base oils typically have a viscosity index of 110 with some high quality oils having a VI of more than 115. They are becoming very common on the market today and are priced very close to Group I base oils.

Group III is the best quality petroleum base oils. They are produced by Hydrocracking, Hydroisomerization, and Hydrotreating which make them much purer than Group I and II. Group III base oils have a VI greater than 120. Although they are produced from mineral feed stocks, high quality Group III candidates closely mimic the characteristics of Group IV synthetic base oils.

Group IV is chemically produced synthetic hydrocarbons (SHC) based on polyalphaolefins (PAO). These base oils do not contain any unsaturated hydrocarbons, sulphur and nitrogen components or waxy hydrocarbons. The absence of these materials results in a very stable base oil with a VI greater than 125, typically 130 or more. PAOs have excellent low and high temperature characteristics, good oxidation stability and are compatible with mineral oils. Polyalphaolefins are by far the most common true synthetic base oil used in automotive and industrial lubricants.

Group V comprises any type of base oil that is not included in the four groups above. Typical examples are esters, polyglycols, naphthalenes, polybutenes, silicones and biolubes. Group V base oils are used for special applications such as gas and refrigeration compressors, very high VI industrial fluids and environmentally-friendly lubricants.  They are often blended with other base stocks to enhance the properties of the oil. A typical example would be a PAO based compressor oil that is mixed with polyolester. Ester oils can endure more abuse at higher temperatures and will provide superior detergency compared to PAO synthetic base oils.

The API categorizes lubricating base oils according to their chemical and physical properties as shown below:

PROPERTY	Gr 1	Gr 2	Gr 3	Gr 4	Gr 5
Saturates	<90%	>90%	>90%	P	O
	and/or	and	and	A	T
Sulphur	>0.03%	<0.03%	<0.03%	O	H
	and	and	and		E
Viscosity Index	80 – 120	80 – 120	>120	>125	R

We rewind the clock some twenty years and replay Mobil litigating Castrol in the USA for ‘falsely’ promoting Group III based motor oils as synthetic lubricants. During 1999 Castrol prevailed in proving that their Group III base oil was

modified sufficiently by hydroprocessing to be qualified as synthetic. Subsequently the API has removed all references to synthetic in their base oil classifications and synthetic has become a ‘marketing term’ rather than a measurable quality of base oils.

Fast forward back to the current scenario and we find that hydrocarbon base oils are typically assigned the following descriptions:

Mineral: Group I and II oils are generally referred to as mineral base oils. Occasionally they are simply described as highly refined base stocks.

Semi-synthetic: Group I and/or II mixed with Group III and/or IV. Such mixtures are also referred to as part-synthetic, synthetic based or synthetic technology.

Synthetic: Based on the 1999 ruling in favour of Castrol, Group III based oils are generally tagged synthetic.

Full Synthetic: The description most often used for Group IV Polyalphaolefin base oils.

Group V base oils are normally specifically identified by their chemical name i.e. polyolester, alkylbenzene, polyalkylene glycol, polyisobutylene, etc. The chemical name is sometimes preceded by ‘synthetic’

Dispute raged in 1999 and still does today. You find all kinds of purists who are populating internet forums and who refuse to recognize Group III oils as “synthetic.” To them it is PAO or nothing. It is best not to get caught up in the synthetic base oil debate. The performance that comes out of lubricating oil is just as important as the base oil that goes into it.  Rather look for oils that offer performance claims backed by industry and original equipment manufacturers’ (OEM) testing. Q8 lubricants are blended with the highest quality base oils available and are supported by a wide variety of industry and OEM approvals.

Foam and air entrainment problems are quite common in lubricating oil circulation systems. Problems that may arise as a result of foaming include fluctuations in oil pressure, oil pump cavitation, loss of oil through breathers and dipsticks and decrease in lubrication and cooling efficiencies. The presence of air bubbles in the fluid can also lead to excessive oxidation. In extreme cases foaming can result in the breakdown of a machine or system.

Most lubricating oils are formulated with antifoam additives. Unlike the name of the additive suggests, foam inhibitors do not prevent the formation of air bubbles (aeration) in oil circulating systems. Air is always to a greater or lesser extent present in circulating oil. Foam is a collection of closely packed air bubbles surrounded by thin films of oil. Antifoam oil additives (usually silicone based) work by reducing the film strength of the air bubbles at the oil/air interface. This results in the rupturing of the air bubbles in the oil causing them to break down and agglomerate. The larger bubbles rise more rapidly to the surface of the oil where they burst readily as illustrated below:

Mechanism of Antifoam Additives

The foaming properties of a fluid are usually determined using the ASTM D892 test method, which measures foam by three sequences that differ only in testing temperature:

• Sequence I measures the foaming tendency and stability at 24°C.
• Sequence II measures the foaming tendency and stability at 93.5°C.
• Sequence III uses the same conditions as Sequence I, except that it is performed on the fluid that has just been measured in Sequence II (See Note Below).

Note: The fluid sample from Sequence I is not used in Sequence II. The fluid sample used in Sequence III is the same sample that was used in Sequence II.

The results are reported as two numbers for each sequence.  For example: 20/0 means 20 milliliters of foam tendency was measured after 5 minutes of aeration followed by no foam stability (0 ml) after a 10 minute settling time. Most new oil specifications require 10 to 50 milliliters tendency maximum after 5 minutes of aeration and 0 milliliters stability after the 10 minute settling period.

Figure 4

This photo of two oils was taken during the five minute aeration period of the ASTM D892 Foam Test. Excessive foam formation can be seen on the surface of the oil on the left which contained no antifoam additive.  The oil on the right was fortified with a foam inhibitor and exhibits negligible foam formation. The photo also shows the larger oil bubbles (that migrate to the surface more readily) in the oil with the antifoam additive.

Although the majority of lubricating oils are formulated with antifoam additives, foam and air entrainment problems are quite common and are usually hard to treat. Traditionally the standard procedure was to run an ASTM D892 foam test on the offending oil, and then indiscriminately add an aftermarket antifoam additive. Generally foam went away quickly, only to return shortly afterwards. More antifoam was added, and the cycle was repeated until the system became so overloaded with foam inhibitor that the oil had to be dumped. Today, there are more practical methods of establishing and treating the source of foam problems and it is therefore usually unnecessary to use aftermarket antifoam additives.

Foaming can be difficult to troubleshoot and for this reason accurate testing to determine the root cause of the problem is essential. The causes of foaming are many. The most common ones include:

• Water contamination.
• Solids contamination.
• Depleted foam inhibitor (possibly due to the use of excessive fine filtration).
• Mechanical issues (causing excessive aeration of the fluid).
• Over- or under-filling of the oil sump/reservoir.
• Cross contamination of the oil with other fluids.
• Contamination of the oil with grease
• Too much antifoam additive by adding aftermarket foam inhibitors.

Although troubleshooting a foaming problem can be challenging, you should be able to identify and correct the root cause through a process of elimination.

If you have any questions regarding foaming or any other lubrication issues, simply mail us at info@bcl.co.za. Our experts are at your disposal and ready to provide you with advice and guidance.

The topic of OilChat #47 (Soot in Engine Oil) raised further questions regarding engine oil deterioration and engine deposits, sludge and varnish in particular. Engine deposits are an ever increasing problem. This is caused by global initiatives to increase fuel efficiency and to reduce pollution of the environment.

Modern internal combustion engines operate at higher temperatures to increase thermal efficiency, oil drain intervals are extended and oil sump capacities are reduced to minimise engine size and weight. To aggravate matters airflow around the engine is reduced as a result of better aerodynamics. All of these lead to increased stresses on the oil. In addition, fuel economy pressures have led to the introduction of lower viscosity engine oils. Thin oils are more prone to ‘breaking down’ at elevated temperatures, hence the introduction of the NOACK Volatility Test. This test determines the evaporation loss of lubricants in high-temperature service. The more engine oils evaporate (vaporise), the thicker and heavier the remaining oil becomes. The collective result of all this is poor oil circulation, reduced fuel economy, as well as increased oil consumption, wear and emissions.

Oil deterioration can occur in the best maintained engines. It can also happen when the oil is still fairly new and it can even occur with synthetic lubricants. A frequently asked question is what the difference between sludge and varnish is.

Sludge is best described as soft black deposits formed in engine oil lubricating systems. It consists primarily of oxidised lubricating oil components, water and carbonaceous residues (soot) from incomplete fuel combustion.  Severely oxidized and contaminated oil can thicken to the consistency of grease.

When hot oil mixes with air, it reacts with the oxygen in the air.  This process is called oxidation and it causes the oil to darken and break down to form acids and sludge.  The acids are corrosive to engine metals and the sludge increases the viscosity of the oil, causing it to thicken and even gel in extreme conditions.  This is significantly aggravated in diesel engines by the presence of combustion by-products. Partially burned diesel fuel (soot) gets into the oil as described in OilChat #47 and increases the viscosity dramatically. Once the oil additives are depleted the oil will break down into a gel that sticks to surfaces inside the engine. These sludge deposits restrict oil circulation and engine cooling, resulting in excessive wear, or in extreme cases, a catastrophic failure of the engine due to lack of lubrication.

Oil sludge usually starts in the top end of an engine (valve cover area) as shown in Figure 1 and in the oil sump (Figure 2).  Immediate damage begins to occur when the sludge or gel blocks the oil siphon screen, as depicted in Figure 3.  Once this blockage occurs, failure of the engine is inevitable.  The oil level may look fine but the engine is actually being damaged with every revolution of the crank as the engine loses oil pressure and is no longer lubricated effectively.  This is a serious issue for many cars built since 1996, hence the introduction of OEM oil specifications such as VW 505.00 and MB 229.3.

Figure 1                                             Figure 2                                          Figure 3

 

 

 

 

 

Varnish is a thin, insoluble, non-wipeable

deposit film occurring on internal engine parts. It is largely caused by oxidation of the oil. Varnish can lead to sticking and malfunctioning of close-clearance moving parts. Engine varnish is similar in appearance to lacquer.

Varnish is the result of engine oil degradation, once again largely due to elevated temperatures and the presence of oxygen in the engine. As the oil flows over hot engine surfaces, it heats up and reacts with the oxygen in the air to oxidise. Each time the oil passes over a hot surface, it oxidises a little more.  This oxidation causes the early depletion of antioxidant additives in the oil, and eventually leads to the formation of insolubles, which is the beginning of varnish. The insolubles agglomerate and sooner or later stick to metal surfaces as portrayed in Figures 4, 5 and 6.

Figure 4                                           Figure 5                                            Figure 6

 

 

 

 

 

Varnish build-up causes excessive wear of moving parts, can lead to bearing failures and may cause critical components to seize. Other common names for varnish are lacquer, pigment, gum, and resin.

Engine oil degradation is aggravated by several other influences as discussed in OilChat #26.  Poor filtration will allow contaminants, wear particles, and water to build up and infest the oil.  This in turn accelerates depletion of the oil additives and allows the oil to foam.  To worsen matters wear debris (mainly copper particles) act as a catalyst to promote oil oxidation.

Blue Chip Lubricants and Q8 high performance engine oils are formulated with the latest generation additive technology to control sludge and varnish effectively. Deposit formation in modern engines is an ever increasing reality, but the advanced additive chemistry in our lubricants minimises engine wear associated with oil deterioration during the life of the oil.

If you have any questions concerning lubrication, or need assistance to select suitable lubricants for your machines, simply mail us at info@bcl.co.za. Our experts are at your disposal and ready to provide you with advice and guidance.

Soot is a by-product of combustion and is present in all used engine oils. Soot is generated as a result of incomplete fuel combustion in engines. When the air and fuel mixture that powers the engine fails to burn completely there is leftover matter – partially burned fuel which is generally known as soot. It is a common misconception that soot does not occur in petrol engines, but it does. Soot is, nevertheless, not such a big problem in petrol engines because they combust fuel more effectively than diesel burners. There are several reasons why soot is a serious problem in diesel engines.

 

To start off diesel fuel is ‘heavier’ than petrol and does not burn as readily as petrol. Secondly, the fuel/air mixture in a petrol engine is ignited by an electric discharge at the spark plug. In a diesel engine the fuel and air ignite spontaneously (auto-ignition) as a result of the high pressure and temperature in the combustion chamber. Furthermore, diesel is only injected into the compressed air in the combustion chamber towards the end of the compression stroke, resulting in poor mixing of the diesel and air. This creates fuel-dense, oxygen lacking ‘pockets’ that produce soot when ignited. Some of this soot comes into contact with the oil film on the cylinder liners. As the piston moves down, soot that is trapped in the oil film is scraped down into the oil sump by the oil control piston ring.

Soot can also reach the oil in the sump via blow-by, i.e. the leaking of partially burnt fuel and combustion gases past the piston rings into the crankcase. This occurs more frequently in engines with worn piston rings. Other factors that can lead to abnormal soot loading of the oil are:

• Frequent stop/start operations.
• Extended periods of idling.
• Incorrect injector spray patterns.
• Rich fuel/air mixtures.
• Blocked air filters.

Individual soot particles are minute and impose little danger to the oil and engine. The soot particles, however, have the tendency to agglomerate (clump together) and form larger clusters. These large clumps of soot can cause damage to the engine, but the dispersant additives in engine oil prevent them from agglomerating and keep them finely suspended in the oil.

When the soot concentration in engine oil reaches a level that can no longer be dissolved by the dispersant additive, the soot particles clump together to form sludge.

The sludge attaches itself to engine surfaces, impedes oil flow through the oil filter as well as the engine and increases oil viscosity with the following devastating results:

• Agglomerated soot negatively impacts the performance of anti-wear lubricant additives and leads to accelerated engine wear.
• Build-up of soot and sludge in the grooves behind piston rings causes rapid wear of the rings and cylinder walls.
• High viscosity results in cold-start problems and risk of oil starvation. This often results in premature engine failure.

Blue Chip Lubricants and Q8 heavy duty diesel engine oils are formulated with the latest generation dispersant additives to keep increased concentrations of soot in suspension for extended periods of time. The formation of soot in modern diesel engines is an ever increasing reality but the advanced additive technology in our engine oils minimises soot induced wear, controls sludge build-up and resists oil thickening associated with high soot levels.

If you have any questions concerning lubrication, our experts are at your disposal and ready to provide you with advice and guidance. Simply mail us at info@bcl.co.za and put us to the test. You can trust us to take care of your lubrication requirements which will allow you to concentrate on your core responsibilities – managing your assets.

If you take a close look at the label on a two-stroke (2T) oil container, it is very likely that you will come across specifications such as API, ISO/Global and JASO. In this final issue of our three part series on 2T oil we will endeavour to explain what this is all about and how to select a suitable lubricant for a specific two-cycle engine.

 

If you take a close look at the label on a two-stroke (2T) oil container, it is very likely that you will come across specifications such as API, ISO/Global and JASO. In this final issue of our three part series on 2T oil we will endeavour to explain what this is all about and how to select a suitable lubricant for a specific two-cycle engine.

The American Petroleum Institute (API) was the first organisation to define a classification system for 2T oils. Of four originally proposed API two-cycle classifications, only one (API TC) is current. Two (API TA and TB) are obsolete, never having been developed further than proposals. The fourth (API TD for water-cooled 2T outboard engines) has been superseded and is no longer recommended.

API TC: These oils are designed for various high-performance engines, typically between 200 and 500 cc, such as those on motorcycles with high fuel-oil ratios. These oils address ring-sticking, pre-ignition and piston/cylinder scuffing problems.

Japanese motorcycle manufacturers found the limits demanded by the API TC specification too slack. API TC oils produced excessive smoke and could not prevent exhaust blocking in high performance Japanese 2T engines. In response the Japanese Engine Oil Standards Implementation Panel (JASO) introduced the following specifications:

JASO FA: Original specification to regulate lubricity, detergency, initial torque, exhaust smoke and exhaust system blocking.  These are medium to high ash mineral based 2T oils.JASO FB: Provides increased lubricity and detergency, reduced exhaust smoke and exhaust system blocking compared to FA. They do not require any synthetic base oils to meet specifications.

JASO FC:  Lubricity and initial torque requirements same as FB, however, far higher detergency, exhaust smoke and exhaust system blocking requirements over FB. These oils may be described as semi-synthetic, low ash lubricants.

JASO FD: Same as FC but with more demanding detergency requirements. Qualifying lubricants are synthetic or semi-synthetic, extreme temperature, anti-scuff, high lubricity, low smoke, and low ash oils.

During the mid-1990s it became clear that the JASO Specifications could not satisfy the requirements of the high performance European two-stroke engines of the time. The International Organization for Standardization (ISO) classifications listed below were developed to address these shortcomings. The ISO basis is the corresponding JASO standard plus an additional three-hour Honda test to quantify piston cleanliness and detergent effect.

ISO-L-EGB: Same requirements as JASO FB plus the piston cleanliness test.  It is generally accepted that API TC rated oils are equivalent to these oils. They do not require any synthetics to meet specifications.

ISO-L-EGC: Same requirements as JASO FC plus the Honda piston cleanliness test. These oils are high lubricity and high detergent, low smoke, semi-synthetic, low ash lubricants.

ISO-L-EGD: Same requirements as JASO FD plus the test for piston cleanliness and detergent performance.  These lubricants are internationally recognized as the highest performance air-cooled 2T oils available in the market place. Qualifying lubricants are synthetic or semi-synthetic, extreme temperature, anti-scuff, high lubricity, low smoke, low ash oils.

Low Ash detergent additives are used in higher performance JASO and ISO 2T oils. These oils are designed for air-cooled, high performance engines that operate under severe load and high temperature conditions. Low Ash detergents keep deposits to a minimum at high temperatures. After these compounds have performed their task, they burn off and are swept away during the normal combustion process. Ash type detergents depend on higher combustion temperatures to clear away. Consequently the use of high performance air-cooled oils in water-cooled outboard or other mildly tuned 2T engines operating at lower temperatures is NOT recommended.

Two-stroke water-cooled outboard motors operate at much lower temperatures than their air-cooled counterparts and are ‘allergic’ to ash type oils. The National Marine Manufacturers Association (NMMA) has very specific lubrication requirements for water-cooled two-stroke marine outboard engines. Ashless oils conforming to NMMA TC-W3 specifications are the only lubricants recommended for use in all 2T outboard motors these days. TC-W3 superseded the NMMA TC-W & TC-WII specifications. It is also important to note that oils designed to meet TC-W3 requirements are not suitable for high performance air-cooled two-stroke engines.

Equally important as the oil specifications is the fuel and oil mixing ratio. Always mix the fuel and 2T oil exactly as the engine manufacturer recommends. Adding too much oil can lead to early ring sticking and plug fouling, whilst too little may result in a lack of lubrication, mainly piston scuffing.

Blue Chip Lubricants and Q8Oils have a complete range of two-stroke oils for a wide variety of 2T engines. If you have any questions concerning two-cycle engine lubricants, our experts are at your disposal and ready to provide you with advice and guidance. Simply mail us at info@bcl.co.za.

When it comes to two-stroke or two-cycle (2T) engine oil every two-stroke enthusiast is an ‘expert’. Some old-timers still believe castor based 2T oil is a gift from heaven, while lots of fanatics can’t resist the ‘pleasing’ aromatic odour of mineral oil being burned in an engine and these days many 2T buffs swear by synthetics. Amid all these opinions there still is a lot of smoke and mirrors and plenty of spin around the subject. In this issue of OilChat we will endeavour to clear some of the fallacies surrounding two-stroke oil.

 

Compared to four-stroke engines, two-stroke engines have far less moving parts. They are therefore less expensive to build, more compact and significantly lighter.  2T engines generally also have a higher power-to-weight ratio than four-strokes. For these reasons, two-stroke engines are ideal in applications such as lawn mowers, chainsaws, grass and hedge trimmers, outboard motors, microlight airplanes, karts, off-road motorcycles and two-wheel racing applications.

2T engines come in a variety of sizes and designs, ranging from tiny little engines for model airplanes to powerful marine outboard motors. Traditionally two-stroke oil was mixed with the petrol, but many recent designs pump the lubricant from a separate tank into the engine. These designs are often referred to as auto-lube systems.  It is still a total-loss system with the oil being burnt with the fuel in the same way as in pre-mix systems.

Considering that 2T engines are lubricated by a mere whiff of oil introduced into the engine in vapour form, two-stroke engine oil must have excellent lubricity. 2T oils must also be clean burning since the oil is combusted with the fuel/air mixture. In bygone days castor-based oils were the preferred lubricant for two-stroke engines due to its high film strength and “wetting ability” (the capability of the oil to spread out on metal surfaces). In addition the chemical structure of castor oil allows it to polymerise at high temperatures to form a sticky wax type material, often referred to as castor varnish. This wax has lubricating properties. In the event of oil starvation the wax separates the metal surfaces for a short period of time.

The down side of castor oil is it that does not burn completely. This results in fouled spark plugs, combustion deposits, piston rings sticking in their grooves and excessive smoke. Furthermore in modern engines where tolerances between parts are much finer, the build-up of castor varnish can lead to degradation in engine performance.

Modern two-stroke engine oils are generally blended using one of the following three base fluids:

Mineral Oils are primarily used for lower performance 2T engines. These oils are good rust preventatives and have great lubricating properties. Mineral oil does not burn all that well and leaves deposits behind when it does burn. Typically a 2T engine running on mineral oil will have gummy deposits in the ring groves and burnt carbon in the exhaust port and on top of the piston. This is a pretty big deal in modern two-stroke engines as gummy parts, fouled spark plugs and carbon deposits mean less performance and more maintenance.

Synthetic Fluids offer the best of everything, including good lubricity and superb combustion properties. With little of the mess that petroleum based oils normally deposit, synthetics leave a much
cleaner engine and therefore maintain maximum engine power for extended periods of time. Synthetic oils also produce much less smoke, but they come at a price premium.

Mixtures of Mineral and Synthetic (Semi-Synthetic) Oils are a compromise that meets in the middle. Semi-synthetics cost less than full synthetic oils. They offer reasonably good combustion and lubrication properties at a more realistic price.

The prime function of two-stroke oil is to lubricate (i) the main bearings on the ends of the crankshaft, (ii) the big- and small-end bearings of the piston connecting rod and (iii) the cylinder walls. To prevent deposit formation in the combustion chamber and on the piston, there is no traditional ash type anti-wear (ZDDP) additive in two-stroke oil formulations and the lubricity is mainly provided by the oil film of the base oil. Many 2T oils contain a high molecular weight polyisobutylene (PIB) to enhance the lubricity of the oil, but this may increase carbon deposit.

Another important function of two-stroke oil is to keep deposits inside the engine to a minimum. High performance 2T oils are therefore formulated with a low ash detergent additive to remove such deposits. Many two-stroke oils are pre-diluted with a solvent to facilitate mixing with petrol at all temperatures. 2T oils are normally dyed blue/green to identify its presence in petrol/oil mixtures. Other additives that may be included in 2T oil formulations are combustion improvers and octane enhancers.

Even if a two-stroke oil has good lubricity, high detergency, resists exhaust system blocking and meets low smoke requirements, how does one know whether the oil is suitable for a particular 2T engine. If you take a closer look at the container or product data sheet you will most probably come across specifications such as API TC, ISO L-EGC, JASO FD, etc. More about this in the next issue of OilChat….

Two-stroke or two-cycle (2T) petrol engines have very specific lubrication requirements. The reason for this is that 2T engines have much higher oil consumption than four-stroke engines due to combustion of the lubricant with the fuel/air mixture. 2T engines also have a higher power to weight ratio than their four-stroke counterparts. To understand the specific lubrication requirements of two-stroke engines one must first look at the way a 2T engine operates.

 

A two-stroke engine completes a power cycle with two strokes (one up and one down movement) of the piston during one crankshaft revolution. This is in contrast to a four-stroke engine, which requires four strokes of the piston (Intake, Compression, Power and Exhaust) to complete a power cycle during two crankshaft revolutions. In a two-stroke engine the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.  Basic two-stroke engines do this by using the crankcase and the underside of the moving piston as a fresh fuel charge pump.

When the piston of a two-stroke engine rises on compression as shown in the illustration on the right, the underside of the piston creates a vacuum in the crankcase. The bottom of the piston skirt ‘opens’ an inlet port in the cylinder, allowing a mixture of petrol and air to flow into the crankcase from a carburetor. When the piston nears Top Dead Center, a spark ignites the compressed fuel/air mixture. The mixture burns and its chemical energy becomes heat energy, raising the pressure of the combusted mixture radically. This pressure drives the piston down the cylinder and rotates the crankshaft. While the piston continues down the cylinder, it begins to expose an exhaust port in the cylinder wall. As spent combustion gas rushes out through this port, the descending piston is simultaneously compressing the fuel/air mixture trapped beneath it in the crankcase.

While the piston descends further down, it begins to expose a transfer port which is connected to the crankcase by a short duct. Since the pressure in the cylinder is now low and the pressure in the crankcase higher, a fresh charge of fuel and air from the crankcase flows into the cylinder through the transfer port. The port and piston are shaped to minimize direct loss of fresh charge through the exhaust port. Even in the best designs there is some loss, but the simplicity of the 2T engine has its price! This process of filling the cylinder while also pushing leftover exhaust gas out through the exhaust port is called “scavenging”. While the piston is near Bottom Dead Center, fuel and air continue to flow from the crankcase, up through the transfer port, and into the cylinder. As the piston moves up again, it first covers the transfer port and then the exhaust port and the cycle is repeated.

If you are still not sure how a basic two-stroke engine functions, please follow the link below. It
shows an animated illustration of a simple two stroke engine and how the 2T cycle works. https://www.youtube.com/watch?v=xNLE8G3pC0k

Most late model two stroke engines have more sophisticated methods of introducing the fuel charge into the cylinder. These designs improve power and economy and include Reed Valves, Poppet Valves, Rotary Valves and Direct fuel injection.  An additional advantage of Direct Injection is that it eliminates some of the waste and pollution caused by carbureted two-stroke engines (where a proportion of the fuel/air mixture entering the cylinder goes directly and unburned out through the exhaust port). Direct fuel injection 2T’s are more efficient because the fuel is injected after the exhaust port closes and therefore more complete combustion occurs and more power is developed.

Since the fuel/air mixture is constantly being pumped by the crankcase and piston, it is not practical to lubricate the two-stroke engine with circulating oil from a sump (like a four-stroke engine) because the oil would be swept away by the mixture rushing in and out of the crankcase. In a 2T engine a little oil must therefore be mixed with the fuel (typically 2% to 5%) to lubricate the few moving components of the engine. Alternatively oil can be injected very sparingly, from a separate oil tank, into the engine with a tiny metering pump. The fact that there is so little oil dictates that two-stroke engines must employ rolling element bearings, which need only a whiff of oil for lubrication.

In the nexts issue of OilChat we will endeavour to clear some of the fallacies surrounding two-stroke oil.  If you have any questions concerning 2T oil in the interim, simply mail us at info@bcl.co.za. Our experts are at your disposal and ready to provide you with advice and guidance.

 

 

It is often asked what the acceptable storage life for lubricants and associated products is. Regrettably there is no simple straightforward answer to this question and to complicate matters, the storage life of the different types of lubricants is not the same.

 

In a recent survey Machinery Lubrication Magazine polled several lubricant suppliers to get their recommendations for lubricant storage life. The publishers were attempting to identify a consensus of opinion, or at least a reasonable range, to share with their readers as a best practice. They found a startling variation in responses and a concerning degree of disagreement. In some cases, those polled were apprehensive to respond, most probably because they have no control over storage conditions once the product leaves their plant. The storage environment greatly affects the estimated shelf life of lubricating oils and greases. The following conditions have a major influence on lubricant storage life:

Temperature – Both high heat and extreme cold can affect lubricant stability. Heat will increase the rate of oil oxidation. Cold can result in wax and possible sediment formation. In addition, alternating exposure to heat and cold may result in ‘breathing’ of drums and possible moisture contamination. A temperature range of -10°C to 45°C is acceptable for storage of most lubricating oils and greases. Ideally, the storage temperature range should be from 0°C to 35°C.

Light – Exposure to bright light may impact color and appearance. Lubricants should be kept in the original metal or opaque plastic containers they were supplied in.

Water – Water will react with some lubricant additives. It can also promote microbial growth at the oil/water interface. Lubricants should be stored in a dry location, preferably inside or at least under cover. When storage of drums outside is unavoidable, they should be placed horizontally (on their side) with the bungs in the 3 and 9 o’clock positions. This allows the water to drain off and not to be drawn into the drum.

Particulate Contamination – Lubricant drums and pails should not be stored in areas where there is a high level of airborne particles. This is especially important when a partially used container is stored for later use.

Atmospheric Contamination – Oxygen and carbon dioxide can react with lubricants and affect their viscosity and consistency. Keeping lubricant containers sealed until the product is needed is the best protection.

The estimated shelf lives on the following page apply to products stored in their original sealed containers, in a sheltered environment, at suitable temperatures and under good housekeeping conditions.  In addition, products should be used on a FIFO (First-In, First-Out) basis. FIFO rotation of stored products will ensure storage life is not accidentally exceeded.

ESTIMATED SHELF LIFE OF FINISHED PRODUCTS

AUTOMOTIVE PRODUCTS	STORAGE LIFE
All Automotive Lubricants (PCMO, HDMO, 2T Oils, ATF, AGO, STOU, UTTO, etc.)	3 Years
Brake Fluids (in their original sealed containers)	1 Year
Antifreeze Coolants	3 Years
INDUSTRIAL LUBRICANTS
All mineral based lubricants	3 Years
PolyAlphaOlefin based lubricants	3 Years
Ester based lubricants	3 Years
PolyGlycol based lubricants	2 Years
Soluble metal working fluids	9 Months
Neat metal working fluids	18 Months
Neat forming oils, protective oils and spark erosion fluids	3 Years
GREASE
NLGI GRADE ≥ 1     Lithium and lithium complex, lithium/calcium complex, aluminium complex, barium and calcium sulfonate grease Aluminium, bentonite clay, calcium & calcium complex, sodium, polyurea and silicon greases	3 Years   2 Years
NLGI GRADE <1     All thickeners	2 Years

 

NOTE: The estimated shelf lives in the table above apply to products stored in their original sealed containers, in a sheltered environment, at suitable temperatures and under good housekeeping conditions.

OilChat #41 dealt with Fuel Economy and Wear in engines as well as the impact of the SAPS (sulphated ash, phosphorus & sulphur) content of engine oils. This newsletter takes it a step further and addresses the significance of high temperature high shear (HTHS) viscosity of engine oil. HTHS viscosity is a critical oil property that relates to the fuel economy and durability of engines. The HTHS test is a simulation of the shearing effects that occur in engines. It is a measure of the resistance of oil to flow under conditions resembling highly loaded journal (crankshaft) bearings in engines running at elevated temperatures and high loads.  Standard HTHS viscosity measurements are performed at 150°C and a specified shear rate.

New global and local government vehicle regulations demand better fuel economy and a reduction in greenhouse gas emissions. One of the ways that this can be achieved is by using lower HTHS viscosity engine oils.  Multigrade lubricants developed for use in automotive engines often contain polymeric viscosity modifiers. The contribution of such viscosity modifiers (VMs) to the viscosity/thickness of oil decreases when the VMs are exposed to the high shear conditions found in critical engine components such as ring/liner interfaces, journal bearings and valve drive components.

Under normal operating temperatures (70°C to 100°C), the HTHS viscosity of engine oil is inversely proportional to fuel economy. HTHS viscosity is measured in centiPoise (cP). It should be noted that 1 cP is equal to 1 milliPascal second (mPa.s) since some specifications list mPa.s rather than cP. Bench tests have indicated that a lower HTHS potentially improves fuel economy at a rate of 0.5% to 2.0% for each 0.5 cP reduction in HTHS viscosity, depending on the engine type and operating conditions.

A too low HTHS viscosity however may affect engine durability. Decreased oil film thickness can lead to boundary lubrication conditions and increased wear. It can also cause lower oil pressure when the engine is idling at operating temperature. Even worse, under high stress conditions permanent viscosity loss may occur due to shearing of polymeric viscosity modifiers. It is therefore no surprise that the Society of Automotive Engineers’ SAE J300 Engine Oil Viscosity Classification System includes HTHS limits to ensure that engine oils can be relied on to provide the necessary lubrication under high temperature high shear conditions. The thinner the viscosity grade, the lower the required HTHS viscosity. For instance, SAE J300 specifies an oil must have a HTHS viscosity of 3.7 cP or higher in order to be classified as a SAE15W40 viscosity grade, whilst the minimum limit for a SAE 5W30 is only 2.9 cP.

HTHS viscosity limits are also incorporated in the latest American Petroleum Institute (API) diesel engine oil specifications:

API CK-4 defines oils for use in four-stroke diesel engines designed to meet 2017 model year on-highway and Tier 4 non-road exhaust emission standards These oils are also suitable for older diesel engines. API CK-4 oils are designed to provide enhanced protection against viscosity loss due to shear and have a minimum HTHS viscosity of 3.5 cP.  API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 Plus, CI-4, and CH-4 and can effectively lubricate older engines demanding these API Categories.

API FA-4 describes certain SAE XW-30 oils specifically formulated for use in selected four-stroke diesel engines designed to meet 2017 model year on-highway greenhouse gas (GHG) emission standards.

These oils are formulated to provide enhanced protection against viscosity loss due to shear and are
blended to a HTHS viscosity range of 2.9cP to 3.2cP to assist in reducing GHG emissions. API FA-4 oils
are neither interchangeable nor backward compatible with API CK-4, CJ-4, CI-4 Plus, CI-4, and CH-4 lubricants. Operators should refer to the engine manufacturers’ recommendations to determine if API FA-4 oils are suitable for use in their specific engines.

The HTHS viscosity requirements of the European Automobile Manufacturers’ Association (ACEA) are a bit more complicated. The three classes of ACEA engine oils are listed in bold below. These three classes are further divided into subcategories to meet the requirements of different engines in each class:

Class A/B: Petrol and Diesel Engine Oils (Higher SAPS)

A5/B5 oils have lower HTHS viscosities (2.9 to 3.5 mPa.s), indicating they provide better fuel economy but they may not provide adequate protection in engines that are not designed for such oils. ACEA A3/B3 and A3/B4 on the other hand require oils with higher HTHS viscosities (≥ 3.5 mPa.s), suggesting they may not be as fuel efficient as an A5/B5 oil, but they could offer better engine protection in certain engine designs.

Class C: Oils for Petrol & Diesel Engines with Emission Control Devices (Lower SAPS)

The categories within the C class are divided along SAPS limits and along HTHS viscosities. C1 and C4 are low SAPS oils, while C2 and C3 are mid-SAPS oils. At the same time C1 and C2 oils have lower HTHS viscosities limits (2.9 mPa.s max), while C3 and C4 oils have higher HTHS viscosities (3.5 mPa.s max). The C5 category has the lowest limit for HTHS viscosity. In order for an oil to meet this specification it must be a mid-SAPS oil and its HTHS viscosity has to be between 2.6 and 2.9 mPa.s.Class E: Heavy Duty Diesel Engine Oil

All categories in this class must have a minimum HTHS viscosity of 3.5 mPa.s to ensure adequate engine protection.  In the E class the SAPS content and the drain interval make the difference. E4 and E6 oils offer significantly extended drain intervals (where the engine manufacturer allows it) while E7 and E9 are designed for extended drain applications. E6 and E9 oils have limited SAPS content, which means they can be used in engines that require these oils, such as Euro VI engines.

To complicate matters many engine manufacturers now also include HTHS viscosity limits in their engine oil specifications. All this may appear rather complex and it is indeed. What you should remember thou is the following:

• Lower SAE viscosity grade oils typically have lower HTHS viscosities,
• Lower HTHS viscosity tends to improve fuel efficiency, which lowers GHG emissions,
• Higher HTHS viscosity affords better wear protection, ring and liner scuffing in particular,
• A careful balance must be found when selecting engine oil.

If you have any questions concerning HTHS viscosity, or need assistance to select a suitable oil for your engines, simply mail us at info@bcl.co.za. Our experts are at your disposal and ready to provide you with advice and guidance.

In this final OilChat of 2018 we debate a rather controversial topic: Fuel Economy vs Wear in engines. It is often believed engine oils that increase fuel economy reduce friction and therefore prolong engine life. This theory is challenged in our newsletter.

To start off we should face the fact that many drivers do not really care about fuel economy. This is confirmed by the number of SUVs, 4X4s, Double Cabs and Bakkies we see on the road. The size and weight of these vehicles are not conducive to great fuel economy. Furthermore, consider how most vehicles are driven. Anyone driving slower than the speed limit to conserve fuel is a danger to himself and other drivers that are not all that concerned about saving fuel and drive at higher speeds.

Vehicle manufacturers, on the other hand, are very concerned about fuel economy. Thinner, low viscosity oils are nowadays being used for three reasons: They save fuel in test engines, viscosity rules have changed, and vehicle manufacturers are recommending thinner grades. Traditionally SAE 20W-50 and SAE 15W-40 multigrade engine oils were used, but today many manufacturers recommend oils as thin as SAE 5W-30 and even SAE 5W-20. This seems ridiculous. SUVs and LDVs, with their brick-like aerodynamics and inherently less efficient four-wheel drive configurations, need powerful, fuel-guzzling engines to move their weight around and vehicle manufacturers recommend thin oils to save some fuel.

Thinner oils have less drag, and therefore less friction and wear. Correct? Perhaps this is true in test engines or engines in light-duty operation. Thicker oils, however, may offer better protection for more severe operations such as driving over mountains, towing a trailer or caravan, overloading, high-speed driving, overheating or dusty conditions. Any abrasive particles (such as dust/sand) equal to or larger than the oil film thickness will cause wear. Filters are necessary to keep out larger oil contaminants. The other side of the equation is oil film thickness. Thicker oil films can accommodate larger contaminants.

To make things worse, modern engine oils must have lower SAPS (sulphated ash, phosphorus, and sulphur) levels since high SAPS oils can damage catalytic converters. Phosphorus is part of the zinc phosphate (ZDDP) anti-wear additive. To reduce SAPS you need to reduce the amount of antiwear additive in the oil. Antiwear additives are important in the absence of a hydrodynamic oil film, such as in the valve drive train (please refer to OilChat #22). On the other hand, if engine wear causes oil consumption to increase, the risk of forming phosphorus deposits in the converter increases dramatically. It, therefore, seems that preventing wear and oil consumption should be a priority. In the past, oil formulators could make a premium product by simply adding more ZDDP. A similar move today would result in an oil formulation that would not support new vehicle warranties.

As wear increases, the efficiency of an engine declines. Valve drive train wear changes valve timing and movement. Ring and liner wear affect compression. The wear reduces fuel efficiency and power output. Efficiency continues to decline as wear progresses. Perhaps optimizing wear protection is the way to reduce fuel consumption over the entire life of the engine? Certainly, engines that have experienced significant ring and liner wear benefit from thicker oils. The use of thicker oil results in compression increase, performance improvement, and reduced oil consumption.

High-mileage lubricants are a relatively new category of engine oils. These products typically contain more detergent/dispersant and antiwear additives than ‘modern’ engine oils. They also contain a seal swell agent (to reduce oil leaks) and are available in thicker viscosity grades than most vehicle manufacturers recommend for new vehicles. Perhaps high mileage may be better described by as soon as your vehicle is out of warranty?

Although thinner oils with less antiwear additive outperform more robust products in fuel economy tests, it is not clear that such products save fuel over the life of the engine. Every engine oil is a compromise. Oils recommended by vehicle manufacturers seem to compromise wear protection under severe conditions to gain fuel economy and catalyst durability. It is important to recognize that the use of engine oil that offers more wear protection will most likely compromise your warranty. Thicker oils also compromise cold temperature flow, which may be of concern, depending upon climate and season.
For out of warranty engines in Southern Africa, the best protection against wear is probably a product that is a little thicker (SAE 10W-40 or even SAE 15W-40) and with more antiwear additives than the oils that support the manufacturer’s warranty.

The best oil for your vehicle depends on your driving habits, the age of the engine, operating conditions and the climate you drive in, but it is not necessarily the type of oil specified in the owner’s manual. If in doubt our experts are at your disposal and ready to provide you with advice and guidance. Simply mail us at info@bcl.co.za.
We would also like to make use of this opportunity to wish all our readers a wonderful Festive Season and a prosperous New Year. We are certainly looking forward to chatting with you again in2019.