At an idle, it shouldn't go below 10 PSI. I would say it shouldn't exceed 80 PSI. Also, it is normal for it to drop lower at an idle. How low is yours getting? Are you hearing any ticking or knocking from the engine?
Finally, keep in mind, if you are not hearing any noise from the engine, it could be something as simple as the oil sending unit which is an inexpensive part that sends the signal to the gauge as to how much pressure there is. It isn't uncommon for them to go bad.
Let me know if this helps or if you have other questions.
Wednesday, June 23rd, 2010 AT 10:29 PM