Re: Black Oil / JTS 2.0 engine
You can diagnose many problems with your car from having your oil tested, it's a machine's blood test. The oil will go black after time due to many different reasons such as contaminents, oxidation and soot content. Oxidation will happen in all engines due to the prescence of oxygen and heat, oxidation also causes a thickening of the oil. Contaminents are of most interest, as they can show what part of the engine (if any) is wearing, this can be extremely useful as you can prevent a huge problem before it happens!