What is the primary function of engine oil?

Engine oil lubricates the engine's moving parts to reduce friction and wear, and it also helps cool components by carrying away heat, cleans by suspending contaminants, and helps seal gaps. Without adequate oil, metal parts would grind together, overheat, and quickly fail. The oil is circulated by the oil pump and cleaned by the oil filter, and it must be changed periodically as it breaks down and collects debris. Understanding lubrication — and why regular oil changes matter — is central to the cooling-and-lubrication topic on the Auto Information subtest.