Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. These additives have several functions, but the primary ones are to neutralize acids and clean the oil in the sump. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to cope with them. When this extra additive load is put into a gasoline engine, the effects can be devastating to performance. The detergent will work as designed and will try to clean the cylinder walls. This can have an adverse effect on the seal between the rings and liner, resulting in lost compression and efficiency.

So how do you know if an oil has been formulated for a gasoline or diesel engine, or even the particular year the vehicle was made? When reading the oil’s label, look for the American Petroleum Institute (API) donut. In the top section of this donut will be the service designation. This designation will start with either an “S” (service or spark ignition) for gasoline engines or a “C” (commercial or compression ignition) for diesel engines. See the example above.

Other organizations have their own codes for the types of oils used in gasoline and diesel engines. They also align with the API’s standards. These include the International Lubricant Standardization and Approval Committee (ILSAC) and the Association of European Automotive Manufacturers (ACEA). API and ILSAC are based in the United States, while ACEA is in Europe. These organizations help to specify automotive and diesel engine oils throughout the world.

There are many things to consider when choosing an engine oil for your car, including the weather conditions in which the vehicle will be operating. For instance, in the middle of winter, you want to select an oil that will stay sufficiently viscus to ensure it flows to the engine’s vital components. The oil’s viscosity is another critical factor for ensuring the engine’s moving parts are sufficiently separated to minimize wear. The oil’s additive package is also important. Too high anti-wear additive levels can cause your catalytic converters to clog prematurely, while excessive detergent additives can lead to piston blow-by, loss of compression and premature oil degradation. If you have doubts as to the type of oil you should be using in your vehicle, be sure to follow the manufacturer’s recommendations.