I have a 95 f150 5.8 351c and when my engine warms up it looses oil pressure. I replaced the oil sending unit but no good. Could it most likely be my oil pump/and or pickup screen

 

What kind of oil filter are you using? If it's the orange Fram, that's more than likely your problem.

 

I believe so but it was like this before the last oil change

 

Our trucks are known for dancing gauges. Does your truck "lose" pressure when you're at a stop, but picks up pressure when you accelerate?

Regarding filters, I would try using a Motorcraft or Purolator oil filter. The filter has a lot to do with oil pressure.

The Fram Extra Guard oil filter is not exactly a quality part. The only Fram that's any good in my opinion is the Fram Extended Guard.

Also, with the oil pressure switch, did you get the one for gauges? There's two different types and sometimes people will pick up the incorrect one.

 

The 351c was long gone by 95, I think you have a 351w.
The problem could be as simple as the wrong type of oil, oil filter, or more serious like worn main or cam bearings, leaking lifters, a pick up screen that is clogging or a worn oil pump.
regards
rikard

 

Regarding oil viscosity, if you're using 5w-30 or 10w-30, you can increase your viscosity to 10w-40 (or 5w-40 if you use synthetic) and that will help the pressure when the oil is hot.

Also, some brand's 5w-30 or 10w-30 is thicker than other brands of 5w or 10w-30. High Mileage motor oil compared to conventional oil is a good example of this. High Mileage oils are thicker and if you don't see the starburst symbol on the bottle, it's more than likely because it's more robust and a little thicker than a standard 30 weight.

 

The 87 I had years ago never showed the correct pressure on the gauge,replaced the gauge and sending unit and still the same. I checked it with a mechanical gauge and never worried about the factory gauge again.

 

Your truck does NOT have an oil pressure gauge That thing on the cluster is just a simple on off if the pressure is 5lbs ormore its on and shows normal less than 5 lbs its off and shows no oil pressure just like an idiot light. check it with a real gauge and if its low or nothing dont run it untill you get it fixed you will toast the engine in a very short time.Bubbabud