[GordonGeesey]

I bought a '65 GTO with a newly-built 400. I got all the paperwork on the engine build, and everything seems legit and done right (reputable builder, quality parts, etc). The guy I got the car from said that the engine builder favored oil volume over pressure. He said that the motor had a high volume oil pump in it. The engine paperwork specified the use of 30-weight oil ONLY.

Here's the thing; at cold-start the initial OP is about 80-85. Revving the stone-cold engine takes the OP to close to 100. The oil seems to warm quickly and settles to around 50-60 at cruise RPM after a mile or two.

But once fully warmed up, at 850rpm idle, the OP is only about 8-10psi. It is unsettling to see the hot OP that low. It goes up to 20-40 at cruise rpm when fully hot. The oil level is full, and the oil/filter are both fresh. No noises from the engine. It runs really strong

When I asked the previous owner if the seemingly low OP was normal, he stated "It has OP, right? Then don't worry about it". He said a full-warmed up engine in otherwise good condition doesn't need much OP at idle with no load on it.

Am I being paranoid, or is this a reasonable and normal explanation for my situation? Would love to hear people's thoughts....

[JLMounce]

A general rule of thumb is 10psi of oil pressure per 1000 rpm. The original 462 that came in my 69 bird when I purchased it from the previous owner made about 10-12 psi at warm idle. That engine lasted 25 years and for a good period of it's life it pinged a good bit because of the combination of #62 heads and a smallish comp 280H camshaft that was put together before I got my hands on it.

I would be more concerned with what it's doing at higher rpms under load. If it's making 60+ psi at 5000 rpm under wide open throttle, it's likely fine and you just have wider bearing clearances.

There's a couple things you can do if you're worried about it though.

You can install an oil cooler which can help your warm viscosity. You can also bump up your idle rpm a bit which should provide a bit more idle oil pressure.

[chiphead]

I am not aware of a high volume oil pump for Pontiac other than a Luhn or something. There is a melling 60PSI pump and a 80PSI pump, same volume. If the oil pressure is going 100 PSI with 30wt, I'd expect it has the 80 PSI pump. Does it go over 65 PSI at high RPM when oil is hot?

Do you know the clearances and parts used? Does is list a PN for the oil pump?

I can't see a reason to run a single-weight oil in a street motor that doesn't have exotic internals. Maybe the builder is old school and is worried about a multi weight oil breaking down at high temps? Modern oils stand up to heat a lot better, it's not 1985.

[mgarblik]

You didn't mention what you are using for an oil pressure gauge. Since yoiu seem to be concerned, the best way to verify the concern is with a known, accurate, mechanical oil pressure gauge. Install one for diagnostic peace of mind. Then report back. If your relying on a factory gauge, they can read all over the map, both low and high, with the same gauge. As far as oil pumps go, Pontiac did make a very small oil pump in the early days, a 5/8" inlet tube and 40 PSI max pressure. But nobody uses them and I have no idea if they are even out there. Probably 90-95% of the Pontiacs running have a Melling M54DS or F54DS pump. Both have the same flow output, a 3/4" inlet tube, with a limit of 60 or 80 PSI. I doubt you have any issues but a test would probably make you feel better.

[GordonGeesey]

The engine builder notes specify the use of Driven-brand HR4 synthetic 10W-30 oil, which is what I'm using. Sorry for my earlier "shorthand" that said just 30-weight.

At full operating temp the observed OP above 3krpm is about 40-50lbs.

I'm monitoring the OP with an AutoMeter mechanical gauge, that is fed from the oil filter housing. I don't have any reason to suspect a faulty/inaccurate gauge reading.

I'm fine with the high OP at cold-start, and the 40-50lbs at (hot) cruising rpm. My biggest concern is the 8-9lbs at hot idle.

[GordonGeesey]

Thanks for your input. Oil pressure at operating temp and cruising RPM is fine.

[JLMounce]

You didn't mention what transmission is in the car. If it's got a manual, try bumping the idle up to around 1000. It's not unheard of to see this provide a bit better oil pressure, slightly cooler idle running and depending on the camshaft and top end selections, can result in lower load at idle, increasing vacuum.

If it's an auto with a loose converter, you can also do that, but if it's got a factory type converter, this may not necessarily be possible.

But, based on what you say about it's oil pressure while driving and the fact that the engine isn't making any weird noises and runs well, the lower idle oil pressure wouldn't be a major concern for me. I might just have an oil analysis done every so often for piece of mind that you aren't wearing away bearings.

[steve25]

I would ask your engine builder exactly what clearances he saw when he assembled the motor and if the crank was cut and or the block was aline honed if he had a hand if that which produced the clearances you now have.

The one time in a 400 motor with 10w40 oil that I saw less then 18 to 20 psi at idle with a 60 lb pump was when my pump check ball was held open by a sliver of gasket material and we are talking a 800 rpm idle speed.

[mgarblik]

So based on your recent post, I agree, your pressure readings are "real". Your not in the danger zone, IMO. If the pressure jumps right up as you describe, I don't think you have anything to worry about. So why is the hot oil pressure somewhat low? Nothing that doesn't require taking the engine back apart to know for sure unfortunately. As you know, oil pressure results from the resistance to flow. So where is the engine most likely pissing out oil at hot idle? It's a long list. 1. oil pump check ball to seat leakage, pretty common
2. aftermarket connecting rods with giant side clearance
3. aftermarket crankshafts with over-wide crankpins, huge fillet radius, used with narrow bearings. (Eagle, very common)
4. undersize lifter OD, worn lifter bores
5. unrestricted oil flow through lifters, especially hydraulic rollers
6. main bearing clearance over .003 on 400, .0035 on 455
7. I may have missed some others.

I would end by saying when I worked at the Pontiac dealer as a mechanic, we had many Buick V-6 powered cars come in during the summer with the oil light flickering or on steady at idle. Especially with the AC on in Drive. 500-550 RPM. The oil light had a sending unit that would close the circuit at 5 PSI. GM issued a replacement sending unit that closed the switch at 3 PSI. That "FIXED" the problem. So I wouldn't fret too much over it.

[steve25]

Look at it this way. If at a hot idle after 30 minutes of driving ( at 55 ) and with 8 psi of oil pressure showing up you do not hear your lifters ticking then your just fine.

However if the day ever comes ( hope not ) when that starts hit the gas to raise up the idle speed and get the car home or have it towed home before damage takes place.

[VCho455]

There may not be just one smoking gun for the idle oil pressure drop. Any 2 or more of the items listed by mgarblik could be marginal and together they cause the pressure drop. It's tolerance stacking working against you.

Add one piece of missed debris in the engine that scored the bottom plate and/or gears in the oil pump upon initial startup and you have yet another contributer to the problem.

The engine in my GTO ran for 80k plus miles with the same oil PSI you have. That included thousands of passes down the 1/4 mile.

Personally I would check it with a second guage or have the current guage checked against a known pressure source. If the guage then is reading correctly I would run it. As it's either that or pull it out and tear it down looking for a smoking gun or guns.

[Hardkor455]

Originally Posted by GordonGeesey

But once fully warmed up, at 850rpm idle, the OP is only about 8-10psi. It is unsettling to see the hot OP that low. It goes up to 20-40 at cruise rpm when fully hot. The oil level is full, and the oil/filter are both fresh. No noises from the engine. It runs really strong

When I asked the previous owner if the seemingly low OP was normal, he stated "It has OP, right? Then don't worry about it". He said a full-warmed up engine in otherwise good condition doesn't need much OP at idle with no load on it.

What if it goes down to zero at idle fully warmed up? 80 cold, 60 warm, but then in drive thru at dutch bros. the temp was closing in on 220 and the oil pressure was at zero

[Half-Inch Stud]

Ima gonna call it: over-Honed cam bearings. As that "process" seems to be pervasive. I suppose you keep driving it to better characterize the combo, and see what happens when a proper viscosity oil is used.

Fun Fact: the Cam Bearing side clearance is always too high.
May want to over-fill the oil pan by a quart or two.

Oil pressure tap at the dizzy may help your confidence in the build.

[i82much]

try m1 0w-40. nothing magical about 30 weight. and it will lower your cold pressures substantially.

[Sun Tuned]

As it pertains to this thread, I’m going to share what I’ve found in the last 4 Pontiacs engines I’ve built in this last year.

The first 2 were both 455’s. What I would consider higher end of the spectrum builds. Kre or edelbrock 325 cnc type head builds. Block end of the deal were both stock cranks with nothing more than eagle H Beam rods and lightweight normal 2 relief pistons. Basically the same block we all are putting together.

Both these guys were in a bit of a hurry, so I got them to order already blueprinted oil pumps from Butler. Now as I understand this these are Schuman pumps? In other words they come to butler already supposed to be fixed and ready to go. 235.00 each I think they were. And they were clean and looked the part anyhow.

Put both in and they went together about 4 weeks apart. Both were 60 lb pumps. Crank clearances on these two builds were .002 on the rods and .0025 on the mains, endplay was .006 on both. Thrust not touched , I got a thing about that. Rod dude clearance in both was if memory serves me correctly right at .018 to .020 .Lifter bores look real good …all that.

With 30W break in oil both had great oil pressure cold right at 65-70 lbs. however when at normal hot idle we looking at 10-15. The one was just a bit higher. By about 5 lbs.

This bothered the hell out of me because I’ve never built an engine with hot idle that low. Until these two I’ve never built an engine I had not prepped the oil pump myself either.

Fast forward about 2500 miles and the one guy decides we pull this engine and sort what’s going on and I agreed. Here’s what we found…

The pump that’s supposed to be “blueprinted “ has gear to pump body clearance of .004. But the biggest issue I found was the bypass ball would not completely seal on its seat. I sprayed a column of carb cleaner on top and watched it literally run right out the bottom of the seat nearly as fast as I sprayed it in.

After working on that for about 15 mins I got it to hold the liquid above the ball under the balls own weight. Put it back together with .0015 clearance. Put it back in car and now hot idle is rock steady at 35, that’s where I’m used to seeing em at.

We’ve since fixed the other one with same results.

So the last 2 I’ve done I just bought standard Melling pumps like I’ve always done and just did it myself.
Have not had first ussue that way. But I will tell you the last two pumps leaked at the check ball seat as well. It looks ok enough. But if you put carb cleaners on top of the ball I’d highly suggest monkeying either that till it’s dry underneath before putting it in service.

[chiphead]

Originally Posted by Sun Tuned

Both these guys were in a bit of a hurry, so I got them to order already blueprinted oil pumps from Butler. Now as I understand this these are Schuman pumps? In other words they come to butler already supposed to be fixed and ready to go. 235.00 each I think they were. And they were clean and looked the part anyhow.

There have been several guys on the pontiac FB groups recently complaining about low idle oil pressure in new motors. I ask where they got the pump and if they took it apart and blueprinted it. The answer every time is " I got it from Butler so I assumed it was good."

A M54DS on Summit is $91 as of today. Somebody is making bank on these "boutique" pumps that still have the same issues as a M54DS.

[Sun Tuned]

I agree about that.

Thing is, in both cases, both put out 65 lbs + when running a drill priming tool. Mine just happens to be a stock points distributor, driven by a Milwaukee electric 1/2” drill.
So likely 350 rpm.

The leaking checkball was the tell tale for me. When hot and the oil thins out ,it bleeds off just enough to have a controlled leak abd oil pressure at idle goes in the you know where.

Now the whole time….i gotta think, surely folks haven’t been using these out of the box, they have to be doing the required extra and not seeing ussue. That’s what happened on the 2 I redid, run fine now with no issue.

So if they say they using em in engines out of the box, either someone not paying attention or I’m the only idiot that got not one but TWO in a row that were culls.

Bottom line : check your stuff period. Save yourself a bunch of extra work.

[tempest1964]

Hey Bob, just curious since I’ve never done it, what did you do to get the check ball to seal properly? Thanks

[Sun Tuned]

I put pump in a vise and did Cliffs checkball mod ,only it felt like a really big Qjet.

Seriously I whacked it about 4-5 times with a pretty good size punch and a hammer until it held a column of liquid.

I almost thought I was gonna have to get serious with it and if that didn’t work I had planned to silver braze a different ball on a rod and break out some valve lapping compound and lap the seat. But that didn’t have to get done.

You know the guys have been talking about using a smaller ball…. I may just try that on the next one.

I’ve always blueprinted my own pumps. But hell, for 235.00 you’d think you could get one that was done. Not me.
I about got sick when we pulled that engine and I pulled that pump cover and put a depth micrometer on it. They never touched that one anyway. Maybe it got missed.
Pump works beautifully now though.

The guy who owned the car wasn’t mad at all about it.oretty goid bit of work to do it again but hey, it worked out.

[mgarblik]

Originally Posted by Sun Tuned

I put pump in a vise and did Cliffs checkball mod ,only it felt like a really big Qjet.

Seriously I whacked it about 4-5 times with a pretty good size punch and a hammer until it held a column of liquid.

I almost thought I was gonna have to get serious with it and if that didn’t work I had planned to silver braze a different ball on a rod and break out some valve lapping compound and lap the seat. But that didn’t have to get done.

You know the guys have been talking about using a smaller ball…. I may just try that on the next one.

I’ve always blueprinted my own pumps. But hell, for 235.00 you’d think you could get one that was done. Not me.
I about got sick when we pulled that engine and I pulled that pump cover and put a depth micrometer on it. They never touched that one anyway. Maybe it got missed.
Pump works beautifully now though.

The guy who owned the car wasn’t mad at all about it.oretty goid bit of work to do it again but hey, it worked out.

I have lapped that ball seat as you described with a stick brazed to a ball. Lapped with 280 grit Clover compound. Takes a little time but that iron is pretty soft so not too bad. It's a real shame virtually everything you buy is total crap. It 's absolutely everything, not limited to Pontiac engine parts. I have had the best bang for the buck just buying a regular M54 DS. Or an F54 if you want an 80 lb. pump. Then I add a thick bottom plate and go through it before use. The Nightmare Performance plate is nice and thick.