An insufficient oil supply usually results in the burning and subsequent destruction of the entire bearing set. Factors contributing to the insufficient oil supply problems include the following: oil pump malfunction; oil pump suction tube problem; idling for extended periods of time, or slow speed operation under load (lugging) during which the oil pump is operating at minimum efficiency; worn or stuck pressure relief valve; low oil level in pan; clogged oil filter; oil line problem (clogged or incorrectly installed); leaking gasket in the lubrication system and incorrect assembly in the lubrication system.
Three other lubrication failures can be caused by the following:
(1) Oil contamination from leakage of coolant is a serious problem especially if the coolant contains an anti-freeze compound like ethylene glycol. This type of leakage is usually found around the O-rings in wet sleeved engines or around defective cylinder head gaskets. Oil contaminated with ethylene glycol forms into a gummy substance which coats the crankshaft journals and bearing surfaces. This reduces the oil clearance space to the point of stopping oil flow through the bearing with subsequent catastrophic seizure.
(2) Incorrect oil viscosity can result in lubrication failure. Oil that is of too high a viscosity (too thick) at colder temperatures or oil of too low viscosity (too thin) at warmer ambient temperatures will not provide the necessary oil film. Eventual burning and seizure are the characteristic results.
(3) Less frequently encountered is an overfilled oil pan. This occurs is overfilled to the point where the crankshaft rotates in the oil causing the oil to become aerated or filled with small air bubbles. These bubbles disrupt the lubricating oil film thus reducing the amount of oil available to carry the load between bearing and crankshaft journal. Excessive heat and possible bearing failure are the end results.