Fuel and lubrication

The only fuel used for automobile operation is specially formulated gasoline, even though diesel fuels are used for many trucks and buses and a few automobiles. 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. Antiknock compounds, principally tetraethyl lead, were added to most gasolines to prevent knocking, a rapid, uncontrolled burning in the final stages of combustion that results in a characteristic "knock," or pinging noise, and may damage an engine or reduce its performance.

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. However it is also affected by combustion-chamber design and chamber-wall deposits. 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. The other chasis joints require soft grease that can be injected by pressure guns. A special grade of light hydraulic fluid is required by hydraulic transmissions. Manually shifted transmissions use heavier gear oil similar to that for rear axles to resist heavy loads on the gear teeth. Gears and bearings in lightly loaded components, such as generators and window regulators, are fabricated from self-lubricating plastic materials.