I know you have a lot of threads about low oil pressure, but I have another question about it. I have a 1990 F150 extended cab with a 351W and 117k miles. It started out with warm engine no pressure on guage at idle. Installed mechanical guage, read 40 psi when cold idle, 0 at warm. Changed filter to Motorcraft, reads around 50 psi cold, between 0 and 5 psi warm. I am running Valvoline Max life 10w30. Do you think changing my oil pump and screen would help? I am thinking the screen may be clogged. It doesn't knock, and has plenty of power. Also, how do you stop that engine light from being on constantly since the sending unit got disconnected besides pulling the bulb?

 

sounds like pickup screen is clogged.

you need to ground the wire that connected to the sender.

 

Wouldn't a clogged pickup screen affect cold oil pressure moreso than the hot pressure because the colder oil is more viscous?

 

when i got my truck it had oil pressure for the first 3 to 5 minutes than dropped to zero.

clogged oil pickup was the problem.

 

Thanks, Sounds like I am on the right track.

 

I think what u should do is trade me trucks cause i have good oil presure, just no movement with the crappy tranny.

 

it is wise to replace the oil pump at the same time.

 

I have had trouble in the past with stripped pump drives. They will grip at certain times, and show no pressure at others. Pull the distributor and look at both pieces- the "socket drive" in the distributor, and the end of the pump drive down the hole. Any time I replace oil pumps, I put in a H/D pump drive. Most times it seems I could have put the original pump right back in.

Bob

 

Oh, and I have also had problems with the relief valve. They can stick and change things.

Bob

 

i also have the same problem with my truck and i was going to replace the oil pump, where is it located and are there more than one.

thanks, chris

 

Well, the unfortunate thing is that the relief valve is right on the pump itself, so by the time you get to it, you might as well put a new pump in. As far as the pump drive, I can't say whether you could break the little clip that keeps it down in the pump and pull it out the distributor hole, but even if you could, there would be no way to replace it once you put the new shaft in. It would probably be fine until you next time pulled the distributor, and it came with it. Maybe I am wrong on this, maybe someone has tried it?
I've also heard of people changing the pump the easy way by cutting a hole in the oil pan, changing the pump and welding the metal back in. Not sure if I recommend that method.
Hope some of this helps..............

Bob

 

But I do strongly recommend when replacing an oil pump to put a H/D drive in it, and look carefully at the hex hole in the bottom of the distributor. It can save a lot of grief.

Bob

 

do you mean h/d like high pressure pump or heavy duty parts?

 

Wow, I'm surprised. No one has asked the important questions regarding this issue.


What kind of oil pressure do you get while driving? You should have at least 10psi per 1000 RPM.

Cold idle should be between 40-60psi...which you've got. Hot idle should be around 20psi for a good standing engine.

Then 10psi per 1000 rpm is the spec for driving warm.

If you have normal/good oil pressure throughout the operation of the engine EXCEPT hot idle....than you have a problem and it is not the pickup screen or oil pump.

When the bearings in the engine get worn the clearances get larger...those increased clearances reduce oil pressure at hot idle. When your oil heats up it thins out and the extra space in the bearings will drop the pressure at idle. When this happens...it's telling you the engine's bearings are worn and need to be replaced (ie rebuild time).

You'll see your idle pressure go from the normal 20psi down to 15.......10.....5....eventually nothing....and by then it's over your bearings are shot. Below 5 and you've violated the "10psi per 1000" rule and you're not getting enough lubrication...so its compounding the problem.


This would save you the trouble of assuming it's the screen or pump and going through that headache of a job for nothing.


If your oil pressure is normal when you're driving it....than you're about due for a rebuilt engine.

 

Well looks like i have a couple of calls to make, my 302 is suppose to be completely rebuilt. What a bummer, so much for a easy fix