F-150 Oil Pump?

Question

I have a 94 F-150 that when started cold has good oil pressure but as the truck warms up the pressure falls to nil and the lifters start knocking. Is this the oil pump or would it be the sending unit. I have had several mechs. look at it and they all have different answers.

Answer 1

You've got all the answers in your question. No, it is not the sending unit. How do I know? Because along with the drop indicated you also get knock. That ONLY happens with lifters starved for oil. DO NOT continue to run the engine until it is fixed.

Drop the pan. Look for sludge in the pan. Clean it shiny clean. Check the screen on the oil pickup tube. Is it coated with sludge? Take it off and clean it really well too. If you're lucky that will solve the problem. If not you will probably have to change out the oil pump. In the event of no sludge, and a relatively clean screen, you will definitely need to change out the oil pump. Not a bad job to do.

Answer 2

It may be that the oil is not returning to the crankcase fast enough and is accumulating on top of the cylinder heads. Check the dipstick before start-up and again when the lifters start making noise.

Answer 3

Sounds like worn cam bearings does pressure drop gradually or all at once?If gradual its probably cam bearings.If all at once and shows full of oil either oil pump or oil pump drive slipping in the distributor.

Answer 4

"oklatom" is right.
You may want to change engine oil AND filter.
Change oil to 20W-50. It's a little thicker and will build a little more pressure than 10W-30.

A plugged oil filter will reduce the flow of oil to the engine reducing oil pressure too.

Answer 5

it's the oil pump here's a link to them cheap on ebay motors