oil pressure gauge

My oil pressure gauge on my 1991 GMC Jimmy has suddenly started dropping on me. It will start out at about 37 or 40 psi then drop down to zero. The jimmy has 103888 miliage. What might be the problem and how serious is it?

Ok theres no way that it would drop to zero otherwise engine would commit sucecide(that was for the people who dont know). If when the car iginition is turned on it lights up properly= you may need to change the sensor itself, you might need the dealer for that one. I need to do the same, whenever the rpm is increased the indicator goes right to the top. I thought that was normal until recently, my uncle used van doesent do that, nor should it on any vechile.

I have a question kinda like above. On my 2001 Jimmy the oil pressure gauge jumps around alot dependent on idle speed. Is this normail? I have not seen it on any other vechile I have owned expect a 1998 Jeep Cherokee. Is it a light SUV thing?

Either the pressure sender is faulty or the wiring is in poor condition: break, loose, shorting.

Oil pressure will fluctuate with rpm changes and with engine oil temperature. This is being shown on your gauge. It is common for oil pressure to be lower on high mileage engines and will show up especially at idle when engine is at operating temperature. Frog05, it could be a serious problem with your oil pressure droping to zero or it could be a faulty gauge or sending unit. To be on the safe side you need to remove the oil pressure sending unit from your engine and install a manual gauge (available at local parts store) this will give you an accurate reading. To see how low your pressure will drop, check at idle with warm engine.