Oil pressure problem?

78250F100

New member
My 78 250ci six has a oil pressure problem. I was using just an idiot light, but when it started coming on I switched to a mechanical gauge. When you start it the gauge shows good pressure and then it steadily declines down to zero. The more gas you give it the quicker it drops. If you shut it off, even for a few seconds, then restart it, the oil pressure comes back and then starts to drop again.

When I got the motor the oil pan was dented but I am pretty sure I got it pounded back out. I don't think it ever hit the screen.

This vehicle has never been driven on the road since the motor was installed. I am trying to get it ready.

Any ideas would be appreciated!
Chris
 
8) measure the distance from the bottom of the oil pan to the oil pick up screen. if you have less than 3/8" then that is certainly part of the problem. you can do with using modeling clay layered on the oil sump, and install the pan to spec. then remove it and measure the thickness of the clay. also check the oil pick up for leaks, if it draws air you can see the same symptoms. next would be the oil pump itself. if the bypass valve spring is weak, or the pump is loaded with sludge, again you get the same symptoms. and while you have the pick up off the engine, check it for sludge in the screen and pipe, again if there that can also be a problem.
 
Just a thought, but maybe it could be an oil drain-back restriction. Good pressure on start-up, but when you rev it, it pumps the oil out of the pan and up into the engine. After shutting it off, the oil drains back and you have pressure again, even though only for a short time.

I can't imagine what might cause this. Usually drain-back problems are related to extended operation at higher rpm.

-Stu
 
stu in wichita":3lrkqwas said:
Just a thought, but maybe it could be an oil drain-back restriction. Good pressure on start-up, but when you rev it, it pumps the oil out of the pan and up into the engine. After shutting it off, the oil drains back and you have pressure again, even though only for a short time.

I can't imagine what might cause this. Usually drain-back problems are related to extended operation at higher rpm.

-Stu

8) drain back issues can also result from sludge build up in the drain back holes.
 
change oil filter as simplest check? Some install anti-drain back filter on sm sixes (just as standard proceed - not necessarily 4 this problem).

Let us know how it goes as you progress.
 
I took the pan off and beat out some more dents and cleaned and checked the pickup screen. I poured gas down from the valve cover to make sure the drainback holes in the head were clear. Everything looked fine, but there was about 3/8" of sludge sitting on the bottom of the pan. I put it all back together after it was clean and the problem was still there.

This morning I stopped at the parts store and bought a new Motorcraft oil filter. Would you believe it, the problem was solved.
I don't know if it was the difference between the Motorcraft and the STP or if the STP had just become plugged from the sludge from the oil pan.

Thanks for your comments and help!
 
"Thanks for your comments and help!"
U fixed it (4 awhile) not us...

Coulda been all those things, but keep ur eye on it, esp. now U have the gage for actual measurements (what does it read?).
BTW: when 'on the light" (before you set up the gage) when did it flicker (or did it actually come on solid red continuously? when?).
 
The gauge reads between 25-50.

The light would come on after it had ran for awhile and once it came on it would stay constantly red until the truck was shut off.
 
that's some good info for some 1 who understands these things (who's not me). I remember the mechanics - in the day, said it made a difference (between flicker & solid on).
Parts will expand under heat, oil thins out.
I don't know if the kero/gas - whatever U poured down there helped. I'd say U'd need a mechanical cleaner (a wire or a brush, c. air may B?).
There is an internal engine cleaner, not sure it's reliability, that U can pour in there as well. (Follow directions closely).
Glad U put in the gage, tried the 3/8 inch p/u-to-pan adjustment and new filter. Not so sure on the kerosene/gas.
 
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