OK, we got the 69 Cutlass back together & on the road. Rebuilt the engine since last OCA show (It blew up before we got a chance to get there, overheated & bent # 5 exhaust valve). Here's the new problem. On start up good oil pressure, about 45 psi. as it heats up it goes to about 35 psi while driving & drops to about 0 psi while idling under load @ 500 rpm. If I put it in neutral it carries about 10 psi at idle (750 rpm). We had the block cleaned & honed for the rebuild. Also turned the crank 10 under & put correct 10 under bearings in. Before it blew, it held 25 psi at idle under load. If the shop didn't put a correct oil galley plug in the back of the block, would that cause the problem? What about setting the idle so under load it's turning 750 rpms? We reinstalled the high volume oil pump that was in it before I haven't pulled the distributor yet to see if it's oiling back there. As always, any help is much appreciated.

 

If the oil galley plug is missing, yes you would have very low oil pressure. If they installed a plug without the hole, that would not cause low oil pressure, but it would be bad news for the dist gear.

 

The oil pressure readings sound way too low for a freshly rebuilt engine, but your idle also seems too low. I'm not sure what spec is for your setup but I know mine is 625 RPM in Drive.

 

Start by using a known good gauge, a mechanical would be best/most accurate.

Oil filters, cheap ones, can cause poor oil psi. And hopefully you've changed the oil & filter after initial startup/break in? Same weight oil as you used before? Some moly based assembly lubes clog filters.

Do you know the bearing clearances? Large clearances also impact oil psi.

You reused the original oil pump? Did you disassemble, check for debris, and clean it? Same with the pan? Debris stuck in the check ball/valve in the pump can cause it to hang open and cause low oil psi.

Start with the gauge, that's my first guess.

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What's your PSI when you rev it up?
Apx 10 psi for every 1000rpms?

It might not really be an issue.
Volume is more important than pressure.

Cruising down the road, I've got about 38psi
When I matt it, I've got 50psi.
When I'm idling in gear when it's hot? It bounces between 0 & 10.
It seems scary, but you may not have anything to really worry about.

But I would check everything the guys here say to do...just to be safe.

-Pete

 

Sounds like your builder didn't add the extra clearance Olds center exhaust guides need. My 40 year old short has way better cold and hot oil pressure numbers. It has 60 cold, 15+ hot idle and 40 to 45 hot at around 2000 rpm with 5W30 Defy oil. Something is very wrong.

 

What does valve guide clearance have to do with oil pressure?

 

It is.

 

He had a the center exhaust valve stick. Was the motor completely torn down after this? Exhaust valving sticking happens way to often by machinist's who don't build Olds V8's.

 

Thanks for all of the input guys. I've been out of town for a week & just getting caught up. I haven't had a chance to try the suggestions yet, hopefully this week. To answer some questions, no I haven't changed the break in oil yet. The engine just has 50 miles since the rebuild. That will be done this week. I am running 10W30 synthetic, planning on going to 10W40 with the oil change. Yes, the engine was torn completely down after the exhaust valve bent. New rings, bearings, valve guides. Yes, I cleaned the oil pump out thoroughly before reinstalling. It was a new high volume pump. I am using a mechanical after market gauge. I'll keep you posted on my results.

 

Break in oil is for startup only, and you dump that after the initial fire up and cam break in, filter too. You do not drive on that oil at all. All contaminates that are trapped during assembly and assembly lube need to be flushed. Because of all that crap in there, you can't get an accurate reading of oil psi.

Also, you are not supposed to break in or do initial start ups on syn oil, should use conventional as stated by the cam manufacturers.

When you cleaned the oil pump, did you remove the check valve plug, spring, and ball and clean thoroughly?

What filter are you using?

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I had a faulty oil pick up screen do the same thing.


Better not drive it until you figure it out.


Mine cost me $4,000 to fix......