Finding the right motor oil for a car begins with a look in the owner's manual. Manuals contain the specific requirements for such items as motor oil, transmission fluid, brake fluid and other replaceable parts and fluids.
It is important to check the owner's manual with care, as many manuals are written for models with multiple engine types, and different engine types take different levels of oil viscosity. The best results come from buying the motor oil that corresponds with the engine in the car. Another place to look for the type of motor oil is on the cap on the crankcase. Removing this cap is necessary to add oil; in many cars, the cap has the motor oil type printed or in raised letters and numbers.