The type of oil a 1991 Ford Ranger takes depends on the engine it has. You need to check your owner's manual for the specific recommendation. However, generally speaking, a 1991 Ford Ranger likely used
SAE 10W-30 or
SAE 20W-40 conventional motor oil. The owner's manual will specify the correct viscosity grade and whether it should be conventional, semi-synthetic, or synthetic oil. It will also state the correct oil capacity for your engine.
Do not rely solely on this information. Always consult your owner's manual for the definitive answer. The wrong oil can severely damage your engine.
