87 f-150 oil pressure problem

[87f150guy]

Hi,

I have a 1987 f-150 with a 4.9L engine with 205,000 miles on it. When I first crank the motor the oil pressure is fine, in normal range. My problem starts after the engine warms up. At normal road speeds the oil pressure gauge indicates within normal range, but when I come to a stop, the oil pressure gauge drops below normal and the red indicator light comes on. Reving the engine brings the oil pressure back to normal and the light goes out. The motor is not making any strange noises at this time and the vehicle runs just like it has since I bought new. What do I need to do to try and find out what the problem is.

1987 F-150
4.9L engine
4 speed manual transmission

[PKRWUD]

If it were me, the first thing I would do is install a known good aftermarket mechanical gauge and verify what the actual pressure is. Then I'd probably buy a new oil pump.