455HO Cold vs Hot Oil Pressure
 

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

10lb per 1000 RPMs is good.Tom

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

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

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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 :D

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. "

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.

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.

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?

While we're on the topic of oil pumps and Pontiac lubrication systems, I've always made some basic assumptions about Pontiac lubrication systems that may not be correct.

As I already mentioned, the Pontiac oil pump is a gear style positive displacement pump. The pressure coming out of the pump is regulated by a valve internal to the pump that limits the maximum oil pressure. I believe it may be possible to exceed that pressure under certain cases (such as a fully plugged filter or something blocking blocking the oil flow). At idle, the engine isn't pumping enough oil to exceed the oil pump pressure setting. As engine RPM increases the flow volume, pressure will rise to where the pressure is limited by the oil pump pressure valve . The oil leaving the pump goes into the oil filter adapter. There is a bypass valve in the oil filter adapter that will divert oil past the filter when pressure gets high enough due to high RPM or a restricted oil filter. At higher RPM, the oil from the oil pump bypasses the filter almost entirely. I think Pontiac engineering did this because they knew some car owners would let their oil filters get dirty, and they felt it safer to bypass the filter than to let the engine starve for oil.

What I don't know is how the bypass pressure setting in the oil filter adapter compares to the oil pump pressure setting. I always assumed that a standard production engine with a 45 psi oil pump was paired with an oil filter adapter that was set to bypass at a pressure slightly higher than the pump pressure. I also assume that an engine with a 60 psi pump has a different oil filter adapter than an engine with a 45 psi pump. What that meant to me was that when I rebuilt an engine and installed a 60 psi pump, I would replace the stock oil filter adapter with one from an engine that came from the factory with a 60 psi pump (Ram III, 70 455HO, etc).

The implication is this: If you put a 60 psi pump into an engine that originally came with a 45 psi oil pump, the pressure of the oil coming out of the oil pump might be higher than the pressure setting of the bypass valve, so you would be constantly bypassing the filter at anything above idle.

The alternative to that is that Pontiac engineering set the bypass pressure in the oil filter adapter high enough that it would work with a 45 or a 60 psi oil pump. That means there would be no difference between the oil filter adapter for an engine with a 45 psi pump vs a 60 psi pump.

Does anyone on this board know the answer to this question?

That's probably going to get into the discussion of blocking the bypass all together and the pros and cons of that.

Yeah, I know.

I just wanted to know if I really needed to change the oil filter adapter when upgrading oil pumps.

I've asked that question before (not necessarily on this forum), and never got a answer I felt comfortable with. I tried to figure out if the part number for the oil filter adapter was different for a standard 455 vs a 455HO, but was never able to find the answer. I'm hoping someone here knows.

Thanks Mike & Formulajones for taking time to explain to me & maybe other novices here how it actually works. I did a bunch of reading yesterday online about those who intentionally block off their bypass to insure all oil is filtered. I know what can happen at wide open throttle, but I have no comment. I also read a post concerning bypass blocking from a very experienced Pontiac engine builder that said, wrong,wrong,wrong. Again I have no comment. I know I'm not going to. I try not to ask too many things on here and be a pest, but sometimes I have to if I can't find in the previous post searches. Oil pressure was one of those subjects I couldn't seem to find much on. The more I learn, more I realize how little I know. Thanks for the education gentlemen.

I wouldn’t worry about asking a question. Most of the people on here are good people and will try to give you an answer in layman’s terms. I ask questions all the time, in fact I’m a little disappointed nobody has chimed in and commented on if the oil filter adapters are different for standard vs high performance engines.

For the average street car, it doesn’t make sense to block the bypass function in the oil filter adapter. There is little to gain, and much to lose.

One thing that has been briefly mentioned on this thread is that it the oil pressure can be different depending on where you measure it. Pressurized oil that flows to the main and rod bearings runs out the sides of the crank journals and returns to the pan. There are oil passages that direct oil to the camshaft bearings, and other oil passages that feed oil to the lifters, which in turn feed oil to the rocker arms and valves. If there is excessive clearance in your main bearings, rod bearings, or in the camshaft bearings, you could be getting insufficient oil to the top end of your engine.

There are a couple of things modifications I make on all of the engines that I have built. There may be some people on the board that will think these modifications don’t help that much, but I’ll throw them out for consideration.

I always remove the lifter galley plugs on the front surface of the block, behind the timing chain. To properly clean a block, you should remove the threaded plugs at the rear of the block and knock out the pressed in galley plugs at the front of the block. The machine shop then should run a rod through the oil passages to insure they are clean and remove any crud that has accumulated there. I then tap the two holes behind the timing chain and install threaded plugs to replace the pressed in plugs. I don’t tap the hole all of the way through the block, because you have to be careful that you don’t block the oil holes feeding the front lifters on the right and left banks. I also use threadlocker on these plugs. I think the SD455 blocks came from the factory with threaded galley plugs on front, all others were pressed in and staked.

The second thing I do is drill a hole in the galley plug behind the distributor gear. At the top of your engine, there is a galley plug located behind a freeze plug on the back of the block (behind the bell housing). If you drill a small hole in that plug before re-installing, it will spray oil on the distributor gear. H-O Specialties used to sell a kit containing a galley plug with a small hole drilled in it years ago. The purpose of this modification is to insure the distributor gear is adequately lubricated. Sometimes a machine shop will accidentally leave this plug out. When that happens, one whole bank of lifters will clatter.

The third thing is optional. There is a galley plug at the top of the block, near where the distributor in installed. If you want to know what the oil pressure is at the top of your engine (which may be different than what you read at the oil filter adapter), you can install a mechanical gauge in that that galley plug hole. The gauge can be installed temporarily for troubleshooting, or permanently if keeping the car stock isn’t a concern.

In another thread, I talked about how I made an engine stand to run in engines using a subframe out of a Trans Am I junked. I always monitor oil pressure at the oil filter adapter and near the distributor during run-in.

1970-1979 350-455 engines all used 6437605 oil filter housing. None other was listed.

Thanks 77 Canamman.

So the 350 - 455 engines all got the same oil filter assembly (6437605) from 1970 to 1979 regardless of which psi oil pump. That eliminates the question of were there different by-pass valves installed for engines with 40psi, 60psi, or 80psi pumps installed.

This was a good article for guys like me that need to ask questions about oil systems: http://www.pontiacdiy.com/pontiac-v-...-system-guide/.

I understand how the oil filter bypass works now...its differential pressure. With the filter collecting contaminates & carbon to the point where oil flow has become restricted at higher RPM's resulting in a pressure drop, the higher pressure oil from the pump forces the spring loaded ball off it seat and opens the bypass as needed. I'm guessing the bypass opens every time the engine goes full throttle to insure continuous oil flow then closes when back to normal operating rpm.
Thanks Pontiac Engineers.

Yes Pontiac did stop using the 80 lbs pump in the 74 model because the same thing that prompted them to restyle the dipstick for the 67 model cars some were running the cars sometimes a qt low or more & the good pump would suck all the oil up top & the crank being bigger were being starved. So rather then telling the cust's to put 6 qts in the oil pan it was easier to change the pump to 60 lbs & that cured a lot of the problem of oil starvation in the big journal cranks. But the 80 lbs pump is still the better pump as they work better & better designed for Pontiac engines. I run 6 qt with a full filter in all my cars & never have a problem. But again Pontiac was on an economy kick along with all of GM so the cust. wouldn't have to spend that extra on the extra qt. of oil to help cut down on maintenance costs. That way it would look as GM cars were lower in the maintenance cost vs the foreign car which were making big in roads in to the US. But as far as other concerns with the 80 lbs pump there weren't any more with it then the 60 lbs pumps. But I have to say that as mentioned before my engine thats in my 73 GTO right now has the M54F 80 lbs pump & cold pressure is right at 80 lbs, & warm idle is at 70 lbs. It goes up to 80 lbs when I hit the gas & if it got to 40 lbs at warm idle I'd be pulling it apart as there would be a problem somewhere. All of my engines have always had good oil pressure at idle & again if it went down by 1/2 I'd know there was a problem with it. While I was still working (GM service mgr.) we had some on these new engines come in & if the oil pressure was that low we would take them down & find the problem, even thou chevy said it was ok most cust. will NOT except that low of oil pressure on an new car or truck engine, & we always found a problem with them when they had that low of pressure. I know if it was my engine I'd be taking it apart to find your problem before it get to be a bigger one & cost you an engine.

Thanks, that solves that question.

As far as I know, all Pontiac V8 motors from the late 60s thru the late 70s were intended to use 6 quarts of oil. I just checked the owners manual for my 1973 Formula and my 1975 Formula, and the capacities section states 6 quarts of oil when the filter is replaced.

I also have experienced fluctuating oil pressure at internet speeds on cars with 3.42 and 3.55 rear ends. Any time I was taking a car on the interstate, I would check the oil level, top it off, and if I were going on a long trip, I would add an extra quart.

I don't think you need anything greater than 60 psi oil pressure on the street.