Low oil pressure at highway speeds, good pressure in streets

[bubba22349]

X2 checking the oil pump drive shaft would be a good idea. That also reminded me of one problem car years ago. A Ford was towed to my shop for repair when the guy had lost oil pressure on the freeway. He had the oil pressure problem a short time before, he had taken it in to a repair shop were they replaced the oil pump and and oil pump drive shaft, it worked for a time but then again lost oil pressure. Pulled the parts out and found that oil pump drive shaft showed signs of some wear the rounding on the hex ends on one end. The fault was from the original distributor's shaft the broached (hex) end was excessively worn, enough so that it barely drove a new oil pump shaft. Replaced with a fresh rebuilt distributor and another new oil pump shaft to fix the sloppiness in fit, and the problem was solved.

 

[RASEC66]

that sounds like it can be it! I remember when I first installed the D.U.I. the shaft didnt reach the oil pump, so then I had to get a longer one. Till now we are mostly looking at valve tightness because we keep pressure but its such a sudden fast drop that it sounds like that is what it is.

 

[nitrousnick]

I had this happen to the 200cid that I had in my mustang. It turned out to be that the engine had too much blow by that it would keep the oil from returning to the pan causing the oil pump to start sucking air. It would only happen on the highway, I had a mechanical oil pressure gauge and used that to find out how fast I could actually go to keep this from happening.

 

[RASEC66]

I now have a mechanical oil gauge, but it does it at just about any speed on the highway, even if Im going around 45-50 on third to 96 in 5th. do you think the distributor and cam being performance aftermarket might be a problem. This didnt happen with the old motorcraft electronic dist.

 

[bubba22349]

I remember when I first installed the D.U.I. the shaft didnt reach the oil pump, so then I had to get a longer one.

Are you sure that you have the oil pump drive installed correctly? Before the pan goes on the drive shaft get's installed along with the oil pump. It's locked into position with a clip at top between the block on the distributor mounting boss, this so it won't pull up out of the oil pump when removing the distributor.

do you think the distributor and cam being performance aftermarket might be a problem. This didnt happen with the old motorcraft electronic dist.

It's doubtful on the cam, unless you used the blocks original (as in old worn) cam bearings without replacement at the time of rebuild, did you install new lifters with that cam?

 

[RASEC66]

Ok, so I have been talking to the machinist and the mechanic, and they both say that the hex either works or it doesnt he says if it were to slip I would loose all oil pressure and not stay at around 20psi. But we are putting in a new oil pump and pickup and will check everything.

this is getting old...

 

[RASEC66]

Now im thinking I need to put in new lifters. would this be a good idea? or a waste of a lot of time since id have to remove the head to do so.