You can classify an engine oil according with three parameters: 1) Physical parameters, like viscosity which is temperature sensitive, 2) Chemical parameters, including the presence of additives compatible with low emission systems, and 3) Performance parameters, namely oil specs, established by international organizations or by Manufacturers (OEMs). In this article we will focus on the latter. 

Oil Specs indicate minimal performance parameters for an oil to satisfy the engine requirements. These specifications often establish some physical and chemical features, but they basically refer to the passing of specific engine tests, which can be both on the test bench and on the field. To establish if the engine oil you are using is correct you have to check the viscosity recommendations and engine oil specifications in the Use and Maintenance Manual and confront them with those indicated in the product's label. 

Performance levels are fixed by International Organizations or by the Original Equipment Manufacturer (OEM). Every OEM has its own internal engine specs like VW 504.00, VW 507.00 or RN0720. Manufacturers’ specs are obviously the most relevant, but they usually come along also with those fixed by some International Organizations. They may imply different performance levels and interval changes in comparison with those set by the OEM. This occurs to let the end user find the product easily in every market and condition. Reference International Organizations are: API, ILSAC, ACEA and JASO. Click on the links below to get more information:

• API Ratings - Engine Oil Sequences

• ILSAC Ratings - Engine Oil Sequences

• ACEA Ratings - Engine Oil Sequences

• JASO Ratings - Engine Oil Sequences

Many OEMs have their own internal engine oil performance levels, which you can find in the Use and Maintenance Manual, but these are always associated with the specs mentioned above issued by International Organizations.

Let's make a real example. Hot topics today are Fuel Economy engine oils and their compatibility with post treatment systems. Fuel Economy oils are low viscosity fluids by definition. The underlying concept is easy. Lower viscosity means a smaller meatus which means lower fuel consumption. But Beware! If the engine is not made to support low viscosity fluids you risk to burn the bearings.

Check your Use and Maintenance Manual carefully. For instance, if you find ACEA C1, C2 or C5, then you need a product with Mid-Low Saps chemistry (medium or low content of sulphated ash, phosphorus and sulphur) and Fuel Economy features. 

How can I choose the right engine oil for my car?

The best recommendation is to stick to the specs and viscosity parameters written by law in the Use and Maintenance Manual of your car or - in case - to expect that your mechanic does it.