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351M loses oil pressure after 10 minutes

I recently purchased a 1978 Ford F150 4x4 that was losing oil pressure after about 10 minutes. Today I pulled the pan while it was still in the vehicle, replaced the oil pump with a new one & replaced the .030 over rod bearings (while I had the pan off), checked the pickup tube which I have heard is typically the culprit, started her up and was pretty happy with it all. took it for a 10 minute drive, got home, & watched the oil pressure gauge drop to "0". *&$#! So, I can rule out the oil pump. The pressure is really dropping off quickly, almost like the oil pump stopped pumping (wondering if the distributer part that drives the pump could be slipping somehow). Could be a cam bearing or something like that dumping out the oil, it's just wierd that it's got REALLY GOOD oil pressure & then nothing. If I remember correctly when I drove it home after I purchased it, the oil pressure dropped off like described above & then after a short time it came back on just as quickly. It's not the pickup tube either. clean as a bell. mains looked OK. top end is just a wee bit noisy (not bad at all) probably due to the prev owner running it in this condition. Any ideas as to what might be causing this? Thanks for any ideas, mike ( snipped-for-privacy@hotmail.com

Reply to
Quasimodo
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I have a reconned 351c which has worse oil pressure than the old motor. It to starts off full gauge then dies off to about 3 scale units when hot. The reason with mine is conrod bearing/s too wide running clearances, in fact I can hear one bearing if I gun the motor between 1500 to 2500 revs.

A high vol pump may help keep the motor going perhaps?

Jason

Reply to
Jason James

"Quasimodo" wrote

How much crud is there blocking the drainback passages under the valve covers and in the lifter valley?

Reply to
MasterBlaster

I'll pull the valve covers this weekend. Once I figure out what the problem is, I'll post back. Thanks for the replies

Reply to
Quasimodo

If you don't find the valve train drain holes clogged with carbon (you'll need to clean the lifter galley too, if they are), then it will probably be time for cam bearings.

Reply to
John Alt

Knew a guy with an old Galaxie (390 eng.) that had plugged oil returns. Seized it up several times on his way to work, until he found a coffee shop in the middle of the trip, then started stopping for a cup in the morning and again after work on the way home. Gave it enough time for the oil to ooze back down into the crankcase, and drove it like that for several years.

Reply to
Ol' Duffer

hmmm, after 10 minutes. Something may be clogging up when heated.Could be a faulty gauge.

Reply to
d8326

The top of the engine is really clean & tight. The crank bearings were in OK condition showing a little wear. It must be a bearing clearance issue. I'm leaning towards Johns comments about the cam bearings. I've just never had an issue like this before. Thanks for the assist.

Reply to
Quasimodo

If you want to fix the problem once and for all I'd have it stripped and all the clearances checked, The rod or bigend bearings number 8 and if too loose will kill the OP when hot, but all should be checked if the reconer left his lunch in the crank-grinding machine.

There are other issues: oil-pump sucking air (not sealed against the block) faulty pressure relief valve (yet to see one) and if the 'M' uses the Cleveland oiling system, poor fitting lifters in their bore though I'm not sure how much this problem contributes to low OP.

The cam bearings are a candidate if for no other reason than they are pressure fed.

Jason

Reply to
Jason James

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