Ford: high oil pressure, pressure relief valve, pan gasket

Question
I have an '89 f-150 with 300 6 cyl. For a couple weeks when driving. Suddenly get a high oil pressure reading. At first assumed faulty gauge or sending unit. Kept driving it assuming high oil pressure on bad if actually really high to blow out gasket or something. I have developed an oil leak which I will fix once I fix the high oil pressure. I have changed the oil and filter. Replaced the sending unit. No change in oil pressure. My next guess would be the oil pressure relief valve. My question is if the relief valve is located on or in the oil pump or somewhere else on the motor. If you have any other suspicions to the problem please let me know. I think the oil relief valve may be sticking closed. After the truck is drove with high pressure reading sometimes the pressure will suddenly drop back down to normal like the valve finally popped open or something. Thank you in advance for your help.

Answer
Hi,

The pressure relief valve is located in the pump, but I would not go there until i have done a live pressure reading at idle and at 2000RPM.

If pressure is still high, I would look at the oil pan gasket= problem for blowing out.  If gasket is pushing out along rail, then you have to remove pan anyways.  If gasket is good and pressure is high, try an oil system cleaner. If that does not fix after a couple of weeks, swap the pump.