Having oil pressure problems.

I have just recently got a 1990 cavalier with a 4 cylender motor. I am letting my sister use it as an everyday driver. She said that when she drives more then 15 miles the oil pressure gage drops to zero. She shuts it down and waits 30 minutes and its fine. The oil is full and there is no oil leaks. I'm confused as to what it could be. I'm thinking that maybe the oil pump is going out, but I'm not 100% sure. If you have any suggestions I would love it if you could help me out. Im not a wis at cars and anything would help. The best way to get a hold of me would be to IM me. Thank you.

I have just recently got a 1990 cavalier with a 4 cylender motor. I am letting my sister use it as an everyday driver. She said that when she drives more then 15 miles the oil pressure gage drops to zero. She shuts it down and waits 30 minutes and its fine. The oil is full and there is no oil leaks. I'm confused as to what it could be. I'm thinking that maybe the oil pump is going out, but I'm not 100% sure. If you have any suggestions I would love it if you could help me out. Im not a wis at cars and anything would help. The best way to get a hold of me would be to IM me. Thank you.

You more than likely have a sending unit going to the electrical gauge in the dash. Best is to use a mechanical oil pressure gauge to test if it is indeed loosing oil pressure or if it is the sending unit. Hook it up so you can observe it while you are driving. Post back results.

When the oil pressure drops to zero have you checked amount of oil in the oil pan. Probable oil return passages from top of engine to oil pan are full of sludge causing slow return of oil to pan.

Does ther engine get very noisey, rattle when this happens?