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Automotive Lubrication System

Updated on December 2, 2016

The engine lubrication system serves two purposes: it reduces metal-to-metal friction and wear between rotating and sliding parts, and it carries excess heat away from the engine. Among the important surfaces requiring lubrication are the crankshaft journal bearings, connecting-rod bearings, wristpins, cylinder walls, piston skirts and rings, camshaft bearings, valve mechanism, and timing gears.

An oil supply of 4 to 5 quarts (or liters), depending on engine size and design, is maintained in the crankcase. A screened, floating oil intake is provided at the suction side of a camshaft-driven lubricating-oil pump. Located in the deepest part of the crankcase, the intake rises and falls with the oil level. Oil is picked up by the circulating pump and delivered at a pressure of approximately 40 pounds per square inch (3 kg/cm) to a main gallery that runs the length of the cylinder block. Branch passages then conduct the oil to the valve mechanism, timing gears, camshaft bearings, and crankshaft main bearings. From the main-bearing journals it flows through the drilled crankshaft to the connecting-rod bearings, passing up through drilled holes in the I-beam connecting rods to the wrist-pins and piston bosses to which they are attached. Cylinder walls and piston skirts are lubricated by oil thrown from rotating parts; excess oil is scraped from the cylinder walls by the oil-control rings and drained back down into the crankcase.

A gauge or signal light on the instrument panel indicates the state of the oil pressure. The oil level in the crankcase is measured either by a graduated "stick" type of gauge or by a direct-reading gauge on the instrument panel.

Prior to 1962, American cars were equipped with breather tubes that discharged unburned crankcase gases directly into the atmosphere. Since 1962, however, they have been equipped at the factory with internal venting devices by means of which these unburned gases are led back to the engine combustion chambers and burned. This ventilation system was devised to reduce air pollution caused by crankcase vapors.


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