1. No, it is not due to the relief valve. The relief valve limits the MAX pressure - for example, if it was super cold and you ran thick oil, you might see 100psi on startup. The relief valve will open at any pressure greater than (say) 50psi so the most you will ever see on the gage is 50psi. But, at 50psi or below, the relief valve is closed and the pump will put out as much pressure as it can.
2. The relief valve is built into the oil pump, spring, ball, and cotter or roll pin. You can add shims or change springs to affect the relief pressure.
3. Then again, if the relief valve is STUCK open, or perhaps if the cotter pin came OUT, the relief valve would fail and oil pressure would drop way down. Since your pressure is down, something changed it seems, I would try to find out what before you rev the engine very much or drive very far. Try changing oil and filter first?
Last edited by DeuceCoupe; 07/06/10 10:21 PM.