'84 Ford F150, Low oil pressure at high speed

When I take my truck, an '84 Ford F150 302 RWD, on the freeway, the oil pressure drops dangerously low, but at an idle it’s fine! I thought oil pressure problems usually happened the other way around.

The problem usually starts when I sustain somewhere around 55mph. I’m okay with replacing my oil pump, I just want to make sure that’s the problem before I pull my oil pan. Any advice greatly appreciated!

I’ve seen this happen before on Ford engines of that vintage.

The cam timing gear has teeth made from a phenolic plastic. From age these teeth can begin to break off the hub and these bits of plastic fall into the oil pan. At idle these bits of plastic sit in the bottom of the oil pan. As the engine speed increases and the oil pump spins faster, the flow of oil begins to draw these bits of plastic into the oil pump pick-up screen until the restriction at the screen prevents oil from getting to the oil pump. Once the engine is idling again, the flow of oil slows down to where these bits of plastic fall off the pick-up screen and the oil pressure is restored.

Drain the oil and inspect the drained oil for small bits plastic. If any are found the gear teeth for the cam shaft gear are coming apart and the timing chain requires replacement. To remove the plastic bits from the oil pan, while the timing cover is off, and with the drain plug removed, pour a gallon of kerosene down the front of the exposed oil pan to flush the bits of plastic out.


Step one should be replacing the oil pressure sender, which might be worn out and giving a false reading…If that does not cure it, the next step is cleaning out the pan and screen as Tester suggested…If you find bits of plastic, you might as well pull the timing cover and replace the timing gears and chain before that lets go…

How many miles on your venerable '84?

I have no idea how many miles it’s traveled. I only bought it a few years ago, and the odo flips every 100k, so who knows? However, the owner before me put a rebuilt engine in it. I rebuilt the carb last year, and it’s pretty much purred like a kitten since then.

Rebuilt engines seldom use plastic coated timing gears, so change the sender and let us know how that works…