Bore Polishing in Diesel Engines Oil OilChat#33


Q8 Formula Truck 7000 15W40, our new top tier heavy duty diesel engine oil, is designed to protect engines against bore polishing. You may well ask how engine oil can possibly do this. To answer this question one needs to understand what bore polishing is and how it is brought about.

When modern engines are manufactured, the cylinder bores are honed (machined) to produce a “crosshatch” appearance with fine grooves from both directions at about 22 degrees from the horizontal (Photo 1). The crosshatch pattern is required to retain oil to ensure proper lubrication and to form a seal between the piston rings and cylinder bores. Bore polishing is characterized by a clearly defined area of bright mirror-like finish on the cylinder bore where the crosshatch pattern is worn away (Photo 2).


4Bore polishing is brought about by a build-up of carbon deposits in the piston top ring land area, i.e. the part of the piston above the top ring (Photo 3). Poor combustion of diesel fuel leads to these hard carbon deposits, which are highly abrasive and scrape away the honing grooves on the cylinder bores. Bore polishing leads to increased oil consumption (blue exhaust smoke) and loss of combustion pressure. This is because the oil film trapped in the honing grooves that maintains the piston ring seal and combustion pressure, is no longer there. Unburned fuel and combustion gases then leak past the piston rings and contaminate the lubricating oil.


The problem is aggravated by the formation of acids in the engine oil resulting from the reaction of these combustion by-products and condensed water. The acidic build-up in the oil causes corrosive wear of engine components. This cycle of degradation results in the engine becoming irreversibly damaged.  The advanced detergent additive system in Q8 Formula Truck 15W-40 protects diesel engines against bore polishing by effectively removing carbon deposits from piston top ring land areas.

A number of engine tests have been developed to evaluate the bore polishing tendency of diesel engine oils. One such test is the CEC L-101-08 procedure using a Mercedes Benz OM501LA engine. In addition to bore polishing, the test also evaluates piston cleanliness, oil consumption, and engine sludge.  Q8 Formula Truck 7000 15W-40 exceeds the requirement of the CEC L-101-08 test protocol by far.

To find out more about what Q8 Formula Truck 7000 15W-40 can do for your engines, please visit