Definition: The amount of pressure created in an engine's oil system by the oil pump. A certain amount of oil pressure is needed to circulate oil throughout the engine and to maintain adequate lubrication. Low oil pressure or loss of pressure is dangerous because it can lead to expensive engine damage. A low oil level in the oil pan, oil leaks, dirty oil, diluted oil (with gasoline), too low a viscosity oil, a plugged oil pickup screen or oil filter, a worn oil pump or worn main bearings can all contribute to low oil pressure. Complete loss of oil pressure usually results from a broken oil pump drive shaft (if the pump is driven off the camshaft). Unless the engine is shut off immediately, it will be ruined. A sending unit mounted on the engine block monitors oil pressure. Oil pushes against a spring-loaded diaphragm, which in turn is connected to a resistor or set of contacts that trigger a warning light if pressure drops below about 4 or 5 psi.
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