Low Oil Pressure
First, note that it is normal for oil pressure to drop as the engine warms up.
But for oil pressure below this, potential causes are:
- Too much clearance in engine bearings
- worn oil pump
- weak oil pump pressure regulator (spring)
Lost Oil Pressure
If your oil pressure gauge reads 0, start troubleshooting by getting a non-electric oil pressure gauge, connect it directly to the engine and see what it reads.
- If that gauge reads OK, but the one on your dash doesn't:
- Gauge could be bad
- If an electric gauge, wiring could be bad or disconnected. Or incorrectly wired.
- If a mechanical gauge, the line could be kinked or disconnected
- If your oil pressure is really at zero, Continue with "Potential Causes" below. Don't drive the car or let the engine idle, it will soon be making banging sounds.
Potential causes for zero pounds pressure:
- Oil has leaked out of engine
- check the oil level!
- gear fell off pump
- drive gear fell off distributor
- shaft of pump broke
- shaft of pump seized and gears ruined
- impeller slipped off shaft
- pressure regulator spring broke
- oil pressure sender broken
- clogged filter (and filter has no relief valve)
- clogged oil passageway
- pressure releif thing stuck open
- debris blocking oil passage (old gasket, or Silicon gasket material or something)
If the oil filter is clogged, you won't lose pressure in the system (unless it is an archaic filter, these days they all have a bypass system).
If the bypass relief in the oil filter sticks open, that won't cause pressure drop. It only means your oil won't be filtered.
Oil filters are nearly foolproof these days.