Oil pressure gauge goes up when car started, but then down to 0

Complete engine teardown.

Do you have under drive pulleys? If so, you can expect that to happen. It does not mean that something is wrong. You may have a high volume oil pump too. I have under drive pulleys on my Camaro and the oil pressure and voltage readings go up. I have never had a problem with that. I would worry when the oil pressure gauge does not move at all $$$$$$.

your pressure sending switch could be going bad id try replacing that first its easier and cheaper. make sure the oil level is not too high also.if all is good then the switch can be bad or the gauge itself.

First we would need to know when this occurs. Asuming the oil level is at the full mark!. If the pressure goes up during acceleration and down at idle when engine is fully warmed up, then this is normal. An engine requires 10 psi of oil pressure per 1,000 rpm ( ex. 20 psi at 2,000 rpm, 25 psi at 2,500 rpm, and so on ) . If the gauge is moving back and forth erratically at idle , i would say the gauge is bad. If it drops to 0 while accelerating I would say your oil pump is bad. If from time to time it seems to work and other times it seems not to work, I would say the oil pressure sending unit for the gauge is bad. If the pump failed you would start to here a Knocking noise from the engine in a short period of time. Use the above scenario's to narrow down what it may be.

yep i do,,,you have a voltage reg on the back of the dash bord its gone potty,,,change it

The oil pressure specification for your engine is 13 PSI at idle hot, 37 to 75 PSI at engine RPM higher than 1600. I suspect your oil pressure gauge sender unit or gauge is inaccurate. I would have a known accurate mechanical oil pressure gauge temporarily screwed into the present oil sender unit to verify actual pressure.

If you have the correct pressure I would replace the sending unit first.

I had the same problem with my 97 Wrangler 4.0..Change your antifreeze, replace with some new 50/50 mix...Also chanke your oil, replace the filter with a mopar filter and use stratght 30 weight motor oil...Solved my problem

Wire on oil sending unit may have fallen off or sensor itself may have gone bad. Check both. If engine has no tapping noises, likely it's not a pressure problem.

If grounding the dash does not work, try putting a mechanical gauge on it and reading actual oil pressure. Pressure does change while driving, but should not wander. With mechanical gauge, check that running hot at idle (in gear if automatic) pressure should not drop lower than 15psi (I'd rather see 20) High reading should be around 40 -50 but no higher.Low pressure indicates a loss of supply or bad bearing on the crankshaft, high pressure may be caused by sticking pressure relief or restriction in an oil passage.

The gage is working because it is coming on sometimes. The oil pressure sending unit on the engine is starting to go. I would replace the oil pressure switch on the engine first.