The oil pump is bolted to the front of the engine and is driven by the crankshaft snout. They have an extremely low failure rate and do not break and stop working, then suddenly magically fix themselves and work again. If there is no unusual knocking noises from the engine, the most common suspect is the oil pressure sending unit. The fastest test is to just replace it, but to avoid wasting money on unneeded parts, a mechanic will use a mechanical pressure gauge first to measure the actual oil pressure.
A "spun" engine bearing will also cause what you described. When the bearing shell rotates away from the oil supply hole, the oil can run out faster and pressure can't be maintained. As that piece of the bearing comes back around and blocks the supply hole, pressure goes back up for a few seconds. That won't continue very long before you hear a loud knocking noise. At that point it's all over, and continuing to run the engine like that will cause a real lot more damage very quickly and will affect any warranty repairs or reimbursement.
Low oil level can cause this symptom too. Often the warning light will turn on before the actual oil pressure goes to "0", and simply refilling the oil will be all that's needed.
Jan 11, 2014 at 6:49 PM
