Lubrication is an essential part of delivering reliable engine function. Whether driving a lorry, a car or using motorsport fuels in high-performance motoring, the right kind of engine oil for lubrication is essential.
As petrol and diesel engines are different, so are the oils required to ensure their continued performance. Catalytic converters are present in both engines to stabilise toxic emissions in the exhaust system before they are released into the environment. Some by-products of fuel combustion can damage catalytic converters, and oils differ to deal with the differences between petrol and diesel and their by-products.
Diesel tends to have an increased AW (anti-wear) load in the form of zinc dialkyldithiophosphate or ZDDP. The catalytic converters found in a diesel engine are manufactured to deal with this issue, which means diesel engine oil is necessary. You do not want to put diesel engine oil in your petrol engine.
Viscosity is an incredibly important property of lubricants. Diesel engine oil will have a higher viscosity than that of petrol engine oil. If diesel engine oil were put in a petrol engine, temperatures could rise due to internal friction. This could damage the engine, and the excess heat can reduce the oil life. Oil of higher viscosity is also harder to pump around the engine and will reduce performance. When using motorsport fuels the correct match between engine and fuel viscosity is of vital importance for performance.
Another difference between the two oils is the additives found in them. Diesel engine oil has more additives in it than the petrol variety, mainly to perform cleaning functions in a diesel engine. Diesel tends to produce more soot and residues, so detergents of various types are required to neutralise these, along with any excess acid and try to keep engine parts free to toxic build-up.
Too much detergent in a petrol engine can have a severely negative impact on engine performance as these additives can try to clean the walls of the engine cylinders and may damage the liner and rings, leading to reduced efficiency and compression.
Petrol and diesel engine oils are quite different, much as jet aviation fuel is different to fuel you can buy at a service station or motorsport fuels. If unsure as to what kind of engine oil you have, always read the label before putting it in your engine.
When looking at the label for your engine oil, find the area where it tells you for what purpose the oil has been designed. It should have something that spells out its service designation with an S that stands for spark or service ignition, which means it can be used in a petrol engine. A C for compression or commercial ignition will indicate that it is for use in a diesel engine. Never try to economise by using oil designed for a different type of engine. The repair bills you may be racking up will buy the right oil many times over.