Diesel oil is the oil you use to lubricate your engine if you have a car or truck that runs on diesel fuel. It should not be used in gas engines, although some oils are on the market that say they are OK to use in either vehicle type. When changing diesel engine oil, make sure to look on the oil cap. This will usually tell you which oil your car needs, otherwise look at your owner’s manual. Diesel engines are designed differently than gasoline engine, so you should choose an oil that is specifically designed for your diesel engine. The process of choosing might come down to regular oil, synthetic blend, or full synthetic. Full synthetic is usually the best option for protecting your engine. It can handle higher temperatures and coat part better than regular oil.