[1971455HO]

It may be nothing, but I wanted to ask. Its been 2500 miles since rebuild. Using Castrol 10W30 w/comp cam break-in (cam lobe protection) dumped @ 500 miles. Replaced with same oil & additive. Got 2000 miles on this oil change. Planned on changing it @ 3000.

Original nodular 3.25" HO crank with standard rod & main journals. Clearances are .0015" rods & .0015" mains, with .009" end play checked at thrust and x2 side rod clearance is .015". I went with the Melling M54DS 60 psi pump. I thought that was the right choice.

Cold (first start-up of the day) oil pressure is rock solid 65 psi. I keep it on fast idle @ 1500 rpm until a little heat (140*-150*) is in the motor before I rev it to get idle down to 700 rpm to back out of the garage. Oil pressure drops to 50 psi after the first 15-20 minutes of driving back roads @ 45-50 mph. Then I get on the freeway. Oil pressure drops to 45 psi after 20 minutes of sustained freeway 65-70 mph driving.
My concern is, lately I have noticed my oil pressure drops to 20 psi @ idle after getting off the freeway while waiting at the traffic light. Slowly goes back up with a pretty good rev of the engine while sitting still. Goes back up to about 35 psi @ 45 mph on secondary roads while at full operating temperature.

What do you think boys...good...OK...bad...OMG? It's a 60 psi pump, not the SD 80 psi pump. SD's were built a little looser. Mine will never see anything above 5500 rpm.

I run 10W30 based on the crankshaft clearances. Didn't want to strain the cam/distributor gears running too thick of an oil. I do live in the South, it's hot down here, 95* at the Pontiac show this last weekend. I know viscosity goes down as temp goes up.Should I be using heavier oil fellas? Maybe 10W40...You boys in Texas ought to know 'bout right now.

one last stupid oil capacity question. I fill the filter full, screw it on and add 5 quarts of oil to the pan. I've adjusted my dip stick with a spacer to reflect that as full. Should it be 6 quarts in the pan instead of 5 quarts?

thanks,
Eddie

[tom s]

10lb per 1000 RPMs is good.Tom

[1971455HO]

Thanks Tom. Believe me,that little factoid is very reassuring. I hope it is right. I read that today on somebody's forum that races Pontiacs. I also read an article online @ the Hot Rod Network called "Oil Pump Observations" http://www.hotrod.com/articles/hppp-...-observations/
and it included comments from Butler Performance that was also enlightening. Thanks for jumping in Tom. It makes me feel better about it.

Eddie

[tom s]

If you run into high oil temps I would use a full syn 10/30 like Mobil 1 unless using a flat tappet cam.Tom

[1971455HO]

Oh yeah...I am running a flat tappet cam. That's the reason for the comp cam additive every oil change.

https://www.summitracing.com/parts/cca-159

Had I only learned sooner! There's serious advantages to roller cams, no break in, no additives, endless profiles, etc. But they do cost a bit. No break in and synthetic compatible are two very attractive trait qualities.

[rexs73gto]

I don't trust any on the shelf oils any more. I only use Brad Penn 10w30 with no oil additive, my engine is a 400 + .60 over. I run the Melling M54F oil pump , thats the 80 lbs pump & with about the same clearances as your engine when I start it up it will go to 80lbs at start up & then goes down to about 75 lbs. as it warms up. After warm up it stays right at the 70lbs mark. I don't use the M54DS pump as thats the one they use/sell for all other Pontiac engine from 326 to 455 & is not a very good pump. This is directly from Melling techs I've talked to. They say not to use it in any type beefed up engine. The M54f pump they put more time into them & they use to come with both the 60 lbs spring & the 80 lbs spring & you could use either one that you feel is good for your engine. The M54F is detailed better. You can also order from Melling the thick bottom plate which is a big upgrade for it. It keeps the pump from caveating & keeps it from losing pressure as you describe. I know it's a pain to change but I would recommend to change your oil pump now to avoid any further oil concerns. Just my opinion.

[Formulabruce]

Pontiac discontinued the Use of an 80 PSI oil pump , believe this was in '73, 455's .There were bulletins on it at our dealership) for a good reason, it was too much and caused many problems. What you see is NORMAL Oil Pressure after break in. 20 Psi is plenty at idle in a stock type engine. GM went to thinner oils and less pressure in later years to also help with fuel economy.
Dist Mod ( hole in the plug) is still a valid and functional idea.
Tom is Right.
Any Good oil with plenty of Zinc, or a ZZDP additive.

[77 Canamman]

The 455 I built several years ago for my police car starts out at 80, then after several miles it levels out to 55 at 2600 rpm. The hot idle pressure in drive with the AC on is 25. I used the M54DS pump.

[Formulajones]

With an engine built as snug as yours (.0015" on rods and mains) I wouldn't think your hot idle would drop to 20 psi no matter what pump or oil viscosity you're running. While it may be fine, it sure seems low for an engine with tight bearing clearance.

I've personally never had an engine, Chevy, Ford, or Pontiac, that would idle hot with oil pressure that low accept for one, and it was just plum wore out.

I even have a 327 here that I daily drove in the 80's, a virgin short block that had never been rebuilt with a stock oil pump, and hot idle in that was always 35 psi, and about 45 psi anything above that. The short block had over 100,000 miles on it. Engine smoked and burned oil, but oil pressure was always good.

For a Pontiac reference, my bird has an aftermarket Melling pump (trying to remember which one now) and hot idle is always 40 psi and never changes with 10w-30 or 20w-50. My clearances are .002" on the mains, and .0015" on the rods, and any movement in rpm the oil pressure instantly goes up without any delay. At cruise it's always around 70 psi with either oil in it.

You'll probably hear from others that what you have is fine, and it probably is okay and may run fine for many years. I'm just saying I never see oil pressure do that on a fresh engine build here.

On a side note, usually what I've seen that causes low hot idle oil pressures with very little pressure movement when rpm climbs are worn cam bearings. The hot idle oil pressure being low doesn't worry me so much, it's when it doesn't respond much to RPM when I start to have concern. Oil pressure gauge should respond much like a tachometer when you blip the throttle.

[77 Canamman]

I've owned 15 Pontiacs, and not one had hot idle oil pressure over 30. Most are 20-25. The main thing is the cruise oil pressure. The spec in the service manual is 55-60 at 2600 rpm

[Formulajones]

I'm not saying that's a bad thing, I'm just saying that I never see that on a fresh build here. From what I've seen here that's more common on an engine that's "worn in" a bit.

What I will say is not normal is what I mentioned above. Low hot idle oil pressure doesn't scare me much, it's when the oil pressure doesn't respond to rpm that is the real concern. That would indicate things aren't happy inside somewhere.

[weranc55]

I think you are fine with that oil pressure. I had a 73 ta in the 80's that for some reason had low oil pressure after a rebuild. When hot on the highway I would have about 25 pounds and at idle I would be around 10 to 15. When cold it would start around 50. Anyway back then I put over 15k miles on the car and never had a issue. I even used a good mechanical gauge.

[72projectbird]

My 73 455 with 80k original miles, completely untouched, would do the same thing. Cold start was around 50psi, after it would warm up to 185F it would be around 20psi at idle. Cruising it would shoot back up to 35-40 psi depending on RPM.

It's a little unnerving, especially when compared to other engines, but apparently that's how these engines like their pressure.

[Formulajones]

What you had 72projectbird, with 20 at idle and 35-40 at cruise, isn't anything that I would be too worried about.

However.... what weranc55 had with 10-15 at idle and only raising to 25 lbs. on the highway,,,yet it was 50 when cold......yeah that's not really acceptable. Engine may live like that but it's not something I would beat on. That type of pressure situation right there is a classic worn cam bearing scenario from my experience.

[weranc55]

Originally Posted by Formulajones

What you had 72projectbird, with 20 at idle and 35-40 at cruise, isn't anything that I would be too worried about.

However.... what weranc55 had with 10-15 at idle and only raising to 25 lbs. on the highway,,,yet it was 50 when cold......yeah that's not really acceptable. Engine may live like that but it's not something I would beat on. That type of pressure situation right there is a classic worn cam bearing scenario from my experience.

Back in the day I would beat the crap out of it and it never blew up. It was my daily driver in college. You might be right about the cam bearing because its not normal but my point was that even with that low of oil pressure it was still fine. Since it was my daily driver I also would haul my Rm 250 on the back bumper.

[Formulajones]

I'd like to think that the difference between then and now is that we've grown older and with that we gained wisdom. Now we know better

[Formulabruce]

I have seen a bunch of engines get new cam bearings which then needed a cam bearing "reamer" to get the cam to spin smooth. I would Not be surprised if this has a Lot to do with lower idle, but plenty cruising pressure.
Formulajones Quote .."On a side note, usually what I've seen that causes low hot idle oil pressures with very little pressure movement when rpm climbs are worn cam bearings. The hot idle oil pressure being low doesn't worry me so much, it's when it doesn't respond much to RPM when I start to have concern. Oil pressure gauge should respond much like a tachometer when you blip the throttle. "

[poncho-mike]

I had a Formula that had only about 5 psi at idle, and 60 psi at anything over about 2000 RPM. I ran it for many years and sold it to a friend, who wrecked it. I bought the car back after he wrecked it, and later sold the engine to another guy for a builder. It had the same oil pressure after the rebuild. It turned out that the oil filter adapter bypass valve wasn't working right. He put a different one on and oil pressure at idle went to 25 psi hot.

[1971455HO]

Thanks Mike, that may be happening to my car. Did your friend replace the entire filter adapter or just the bypass valve. Is there a way to test them off the car?

I’ve read everything today guys...thanks for all your input.

[poncho-mike]

1971455HO, I don't think you have a problem. My oil pressure was about 5 psi hot, and that is way too low. It should be at least 10 - 15, and 20 - 25 is about normal for hot idle.

The oil pump is driven off the camshaft, and is a positive volume type pump. There are two types of pumps in general, constant volume and constant pressure (for a given RPM). The Pontiac oil pump is a constant volume type of pump, so in the absence of a valve used to create pressure, you would only see the back pressure of the system. That is why the best place to measure oil pressure is at the top of the engine near where the distributor is, and not at the oil filter adapter. I am pretty sure the purpose of oil filter adapter bypass is to build a minimum amount of pressure at the pump, and then bypass oil to achieve a max pressure. I also think there are two different oil filter adapters, one for 45 psi and another for 60 psi.

In my college days, I was an intern for a company that manufactured constant volume pumps. These pumps were used for applications such as pumping crude oil out of the ground at a well, circulating lubricating oil in submarines, etc. We used to test these huge pumps and they would be pumping thousands of gallons of oil a minute, and the pressure at the pump would only be about 5 psi. We had a valve you could use to make the system build pressure by restricting the output path in order to measure the output at a specific pressure. As the restriction caused pressure to build in the pump, the amount of volume decreased slightly as some of the oil would recirculate in the pump.

I wasn't too worried with the low oil pressure at idle because my lifters never ticked and pressure went up with RPM. I will also venture a theory here that running at maximum pressure all the time isn't good for you. If you're at max pressure, I am pretty sure part of the oil being pumped is bypassing the filter element.

Anybody else want to chime in here?