my oil pressure light has been coming on in my car so i hook up an oil pressur gauge to it. for about 10 minutes everything was good then after driving for a little bit my oil pressur went to 0. so i cut the car off and cranked it back up then my oil pressur come back for a few minutes and then went away again, but my top end is still getting oil and nothing is knocking so i drove it around and nothing went wrong any ideas.