Oil Pumps & Components

The oil pump draws oil from the oil pan and circulates it through the engine’s oil galleries to lubricate and cool critical engine parts. The film of oil thus created prevents metal-to-metal contact that would result in wear and damage, and reduces power robbing friction. The pump can be mounted in the crankcase and driven by a shaft from the distributor or mounted on the front of the engine and driven by the crankshaft.

A typical oil pump has a drive and driven gear that are meshed inside a housing. A pressure relief valve regulates engine oil pressure. The oil pump draws oil from the pan through a pickup tube, which may be attached to the pump or the block. A screen at the end of the tube filters out large particles that could damage the pump. The pump output goes to the oil filter before circulating through the engine, for further filtration.

Oil pumps are generally very durable, but nevertheless the pump should be replaced or at least inspected when an engine is rebuilt. Once the pump is disassembled, inspect the housing and gears for scoring, nicks or other damage. The clearance between the gears and between the gears and housing should be checked against specification. Make sure the oil pressure relief valve moves freely. Rebuild kits are available for some pumps that include new gears, pressure relief valve springs, and the necessary seals and gaskets. The pickup tube and screen should be thoroughly cleaned to ensure unrestricted oil flow.

There are several variations of crank driven oil pumps. On a direct drive pump the pump surrounds the crankshaft and the drive gear is mounted to the end of the crank. On gear drive and chain drive pumps, the pump is mounted to the side of the crankshaft and driven by a set of gears or chain and sprockets. The gears or chain and sprockets should be inspected carefully and replaced if necessary. On crankcase mounted pumps, the oil pump driveshaft should be inspected for damage, especially for rounding of the hex at each end of the shaft where it contacts the distributor and pump.

Oil pressure switches and sending units are threaded into the engine oil galleries where they are directly exposed to engine oil pressure. A switch is used with a dash light. If oil pressure falls below a predetermined pressure, the switch will illuminate the light, alerting the driver that oil pressure is dangerously low. A sending unit is connected to a gauge that displays the amount of oil pressure. Oil pressure will be lowest at idle, but should rise as engine RPM increases. Oil pressure varies according to engine design; check the vehicle service manual specifications to see what is right for your engine.