The things in a good fuel for automobile are proper volatility, sufficient antiknock quality, and freedom from polluting by-products of combustion. The volatility is reformulated seasonally by refiners so that sufficient gasoline vaporizes, even in extreme cold weather, to permit easy engine starting. Small lead deposits on such places as engine-valve seats improve valve life. Antiknock quality is rated by the octane number of the gasoline and depends primarily on the compression ratio of the engine. In the early 1990s regular gasoline carried an octane rating of 87 and high-test in the neighborhood of 93.
Lubrication is an essential requirement for all vehicles.
In its absence, friction would increase power consumption and damage the parts. The lubricant also serves as a coolant, a noise-reducing cushion, and a sealant between engine piston rings and cylinder walls. The engine lubrication system includes a gear-type pump that delivers filtered oil under pressure to a system of drilled passages leading to various bearings. Oil spray also lubricates the cams and valve lifters. Fairly stiff grease is required by wheel bearings and universal joints.