Oil return problems?

Duane

Well-known member
I've had a problem since I built the last 250, on the highway, it loses oil pressure around 2500RPM for a few miles. After years of putting up with it, I noticed it did it really bad once it got a little low on oil, and you could just tap the brake, without taking your foot off the gas (steady RPM) and the pressure would fluctuate, so I knew it was sucking air. I took the oil pump out, and sure enough, where the pick-up is brazed to the tube, there was a hole. New pick-up tube, and the condition is better, but it still has problems. I think there is a problem in the returns from the head, because I can kick it in neutral, or shut it off a second, and oil pressure is good for a few more miles. Motor is not sludged, so I was wondering if anyone knows of oil return mis-match problems. Gasket or holes?
 
A couple of thoughts

I ran into something similar a while back. When the tranny was being changed a floor jack was under the sump of the oil pan. The pan bowed in, and that resulted in the pickup being too close to the bottom of the pan. The oil couldn't suck in fast enough. Removing the pan and massaging it with a rubber mallet solved the problem.

My second thought is the opposite solution of the first thought. Did you check to see if your pickup is LOW ENOUGH in the pan? Put a chunk of clay or something on the bottom of the pickup screen and test fit the pan to see how much clearance you have.

My third thought is to completely ignore the dip stick. Change oil (add the full five quarts) and filter. Run for a few minutes to fill the filter, and then pull the dip stick to see if the "F" really is full. Where-ever the oil level is your TRUE "Full".

Good Luck
 
It never totally loses oil pressure, I just see it fluctuate around 40psi, then the lifters start making racket. I had thought I saw somewhere about drain holes being a problem, I know some of the 460 guys have problems with them. I may just have some worn lifters, they were cheap rebuilder ones. The new one is about to go together, and this motor will be retired.
 
Duane;
The return holes in the I6 heads are over 2" long by almost 1" wide, 3 of them. Plugged up returns are highly unlikely.

In the Ford FE family (332-428 cu. in.), the return holes are small, about 3/4". These are known for plugging, as are the ones in the 292/312 and some 'M' series blocks, like the 460, if poorly maintained.

However, my I6 had a very similar problem, which, as mentioned above, turned out to be the pickup tube being too close to the pan. Someone had run over a parking block with the car before I got it, which bent the oil pan upward about 1/2". This would cause the pump to starve at engine speeds over 2000 RPM, and the gauge would fluctuate up and down. The lifters would get noisy, too.

Removing and straightening the oil pan completely fixed the problem.
 
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