Low Oil Pressure

[Tiggie]

It's not a Panther, but I recently got a '68 Mustang with a '70 302, likely original to an F100.

Been checking engine health. Compression is 110-120psi - decent I suppose. Oil pressure is low though. Initial test gave me 30psi cold idle, 40psi cold 2K RPMS, less than 5psi hot idle, 15psi hot 2K RPM.

Changed the oil with 10W-40 and new FL-1A. Got 40psi cold idle, and 42psi cold 2K rpm. Got 10psi hot idle and 20psi hot 2K rpm.

My old '82 LTD with a sludged up 302 and 0psi hot idle oil pressure still held 55psi cold idle or 2K rpm. My '88 wagon holds also holds 55psi cold, but drops to 20 at hot idle. Classic bearing wear in my book.

Why is the Mustang only peaking at 42psi? I was expecting the 55psi. I know it has higher miles in it and has never been rebuilt, so I am expecting some bearing wear. Shouldn't it have more than 40ish when cold? Could this (for once) be an oil pump problem rather than excessive bearing clearance? I was contemplating a partially open relief valve...

Also should mention that the valve seals are chunking - maybe a partially blocked pickup to blame?

Thoughts?

[Lincolnmania]

yea oil pump is probably weak, a fresh one may help oil pressure

[t65neon5]

we are talking about a motor that is 40+ years old......I would imagine that the oil pump would be weak,and unless the oil was changed VERY religiously, you probably have at least a partially clogged oil pickup , possibly clogged oil passages as well.if it runs decent,its probably time for a ring and bearing job at least. I would certailly drop the oil pan,and remove the intake and check everything(main bearing clearences ,oil pump , oil galley etc....)

[gadget73]

Probably the bearings are tired. Its making oil pressure, so its not that bad. Oil pumps don't really wear out very much, and I wouldn't expect a new one to do a whole lot for you but if getting the pan off isn't a huge ordeal, it might be worth swapping it and replacing the pickup just for peace of mind.

[grandpaslincoln]

Does it make noise at all?

[GM_Guy]

You are comparing readings from the same guage?

[King_V]

I thought that normally, cranking compression, even on low compression engines, was supposed to be somewhat higher.... but don't hold me to that.

What's considered normal for say, a low-compression 70s era engine, assuming minimal wear?

[sly]

time to make it a 306 with forged internals and boost

[Tiggie]

The valve seals are chunking, so a clogged pick up is a real possibility. Will pull the pan after I install valve seals. That way I can check the pick up and maybe even take a look at a bearing or two. It smokes like crazy now... If it still smokes after valve seals, I'm just going to pull it out and swap in another 302 I have.

It isn't making noise except for an occasional lifter tapping when hot - I am assuming from low oil pressure. It seems to just be one. This thing has been sitting 10 years so it could be sticking some too. Oil pressure readings in first post are from the same gauge as used in the '82 LTD so it should be a similar comparison.