Engine oil deterioration and deposits: what you need to know!
In our previous blog, we explored the issue of soot in engine oil, which sparked a wave of questions about engine oil deterioration and deposits—specifically sludge and varnish. Let’s dive into how these unwanted by-products form and how they impact your engine.
Why Are Engine Deposits Increasing?
Modern engines are all about efficiency and lower emissions, but these advances come at a cost. Engines now run hotter to improve thermal efficiency, oil drain intervals are extended, and sump sizes are reduced to make engines lighter and more compact. Add to this tighter aerodynamics that reduce airflow around the engine, and you’ve got a recipe for added stress on your engine oil.
Fuel economy demands have also led to the widespread use of lower viscosity oils. While great for efficiency, these thinner oils break down more easily at high temperatures. That’s where the NOACK Volatility Test comes in—it measures how much oil evaporates under heat. When oil evaporates, the remaining fluid thickens, leading to poor circulation, reduced fuel economy, increased oil consumption, and even more wear and tear on your engine.
Sludge vs. Varnish: What’s the Difference?
Both sludge and varnish are by-products of oil degradation, but they differ in appearance and impact.
Sludge is a soft, black deposit that forms in your engine’s oil system. It’s primarily made up of oxidized oil, water, and soot from incomplete combustion. As oil oxidizes—especially when exposed to heat and air—it thickens and forms acids. These acids corrode engine metals, while the sludge increases oil viscosity, eventually turning it into a gel-like substance that blocks oil flow.
Diesel engines are particularly vulnerable because soot from partially burned diesel mixes with the oil, accelerating sludge formation. Once the oil additives are depleted, the sludge hardens and sticks to engine components, restricting circulation and cooling. This can lead to excessive wear or even catastrophic engine failure.
Sludge often starts accumulating in the top end of the engine (under the valve cover) as shown in Figure1 and in the oil sump (Figure 2). If it clogs the oil siphon screen (Figure 3), oil flow stops, leading to inevitable engine failure. 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, on the other hand, is a thin, sticky film that forms on internal engine parts. Unlike sludge, varnish is hard and non-wipeable. It results from the gradual oxidation of oil at high temperatures. As oil passes over hot engine surfaces, it oxidizes a little more each time, depleting antioxidant additives and leading to the formation of insolubles. These eventually stick to metal surfaces, creating varnish. Varnish can cause moving parts to stick, leading to malfunctions, excessive wear, and even component seizure (see Figures 4, 5 and 6. It’s often referred to as lacquer, pigment, gum, or resin in the industry.
Figure 4
Figure 5
Figure 6
Other Factors Accelerating Oil Deterioration
• Poor Filtration: Contaminants, wear particles, and water can build up, degrading the oil and accelerating additive depletion.
• Wear Debris: Metals like copper act as catalysts, promoting oxidation.
• Foaming: Contaminated oil can foam, reducing its ability to lubricate effectively.
The Solution: Advanced Lubricant Technology
At Blue Chip Lubricants, we understand the challenges modern engines face. That’s why our high-performance Q8 engine oils are formulated with cutting-edge additive technology designed to combat sludge and varnish. Our oils help minimize deposit formation, ensuring your engine stays cleaner and runs longer.
Need Expert Advice?
If you have questions about lubrication or need help selecting the right oil for your engine, reach out to us at info@bcl.co.za. Our team of experts is ready to assist you in keeping your machines running smoothly.
Stay tuned for more insights on keeping your engine healthy and efficient