DIAGNOSING ENGINE OIL LIGHT STAYS ON AFTER ENGINE IS STARTED
by Kyle McFadden
The engine oil light remains on after the engine is started. The light may flicker or glow dimly.
The oil light is turned on by an oil pressure sending unit. The sending unit provides the ground to the light when the oil pressure becomes too low. The sending unit is calibrated by the manufacturer but usually activates between 5-10 PSI. The oil light should come on with the key on and the engine off and go out shortly after the engine is started indicating proper oil pressure.
Low oil pressure can be caused by a worn oil pump, worn engine bearings, electrical defect or a malfunctioning oil pressure relief valve. Of course, low or no oil in the engine can also cause this symptom. The first step in the diagnosis is an oil level check. Since all of the other causes usually require major engine service, you should verify that the engine actually has low oil pressure (thus causing the oil light to come on and stay on). This should be done to ensure there is not a malfunction in the oil light circuit. Confirm the oil pressure by removing the oil pressure sending unit and temporarily installing a test gauge. On most vehicles, the oil pressure on a hot engine at idle should be at least 8-10 PSI. If the oil pressure is satisfactory, the most likely cause is a defective oil pressure sending unit. Confirm this by temporarily disconnecting the wire. If the light remains off, replacement of the oil pressure sending unit will be necessary. If low oil pressure is confirmed by actual measurement with a gauge, internal engine service will probably be necessary. You should consult a vehicle service repair manual for specific repair instructions for your vehicle.
PRECAUTIONS, TIPS, and NOTES
Use caution when working around hot and rotating engine parts. Engine oil becomes extremely hot after the engine is operated for only a few minutes. Use caution when removing any component that seals or contains hot engine oil.
has an affinity for Pale Ale and tooling on his 1956 Chevrolet Nomad