Today I ran out of my preferred engine oil for a Diesel smart car. So I ordered oil from my parts supplier specifying that I need Synthetic 5W40 Diesel engine oil. When my oil arrived I noticed that the oil sent was Castrol Edge, an excellent oil. As I checked the specs on the back of the package I found that this oil is not intended for Diesel engines. So after a quick call to the parts supplier they had nothing to the specs needed for the car I was working on. So the customer and I went to Canadian Tire to get oil and wow so many choices. We spent about 15 minutes finding the right oil. So we are looking for synthetic oil which eliminates a lot of the choices. Now we need to get an exact product. Engine oils are rated with what’s referred to as an “API” rating. This is the American Petroleum Institute. There are 2 main classifications of oil Spark ignition and Compression ignition. Gasoline engines are Spark ignition engines, and diesels are compression ignition engines. So we are looking for an API rating beginning with a “C”. Next is a sub category. We are looking for a “J-4” rating, which means the product is exhaust emission safe. Typically low ash, low sulfates when the oil is consumed and burned by the engine, which is normal in a diesel engine.  will not plug up in the exhaust system’s emissions components. So in our case there were 2 products that met our requirements. Mobile 1 Formula M and Rotella TT.  Now in a jam any oil is better than no oil, however prolonged use of “substandard” oil can do harm and void warranties.

The best word of caution I can offer is avoid the advice of the person that says something like “I have had diesels my whole life and never had a problem.” The concern here is with our industry changing so quickly that despite a product that has worked amazingly in the past, modern technology may require a better product and use of that older amazing product could result in a major repair not covered by warranty.

So how do you, the consumer choose your oil? Easy. Read your owner’s manual. The owner’s manual will give you the exact API rating you need so that you can easily identify what is right.