[scott-462]

Changed my oil and filter the other day. Engine has maybe 600 miles on it. When i fired the engine the first time (0 miles) it had apprx 95 psi cold and i cant quite remember how much when warm. Since the first hundred miles or so it now has 85 psi cold and 20 psi warm in gear at idle. I was a little concerned about only having 20 psi with a high volume pump. Its an M54F or something like that 80 psi pump. But i've read 20 in gear at idle wouldnt hurt anything and there isnt any strange noises so i continued to drive it and the PSI hasnt changed any after the first 100 miles or so. But after changing my oil the other day it still has apprx 85 psi cold, but down to 10-12 psi warm in gear at idle. Thats a little too low for comfort, or am i wrong? I had used a conventional oil with a bottle of zinc additive at first but when i changed the oil the other day i used the rotella diesel engine oil as suggested by a couple PY members and the guy at the parts store due to this type of oil having an increased amount of zinc in it compared to regular oils of today. So to sum it up, I went from 20 psi warm in gear at idle, to 10-12 psi warm in gear at idle after this oil change. Is it the rotella diesel engine oil that caused the loss of PSI, the new filter, or whats going on here? And is 10-12 psi dangerous at idle? It rises quickly with RPM.

[steve25]

You need to find out whats going on, as something is up, so stop running the motor!
Your gonna need to pull the pan and drop the pump off and check for crap holding the check ball open, if that checks out ok your into bearing problems more than likly I`am sorry to say if the valve train is not making noise.
I drove a 400 every day for 6 months with low oil pressure due to crap in the pumps check valve, and I had what you see now, that being 12 psi at hot idle.
The motor never saw over 3500 rpm for those 6 months, and 28 psi kept it alive at 3500 rpm.
When I pull it apart all was still fine.
Its been said that you only need 5 psi at hot idle to keep the bearings afloat, I would not want to have to find out if thats true or not, so bit the bullet now and pull the pan even if it comes down to pulling the motor to do so.
Also with the high pressure pump I hope that you used a hardend oil pump drive shaft as the stocker will not hold up long with 95 psi of cold pressure, so check that item out also when you get at it and make sure its not twisting up on you.
The stockers have a line running down the side that makes it easy to see such, the aftermarket ones do not.
Don`t test your luck whatever you do!!!

[1967Tempest]

In an older motor I would say that this isnt a big deal. My mothers Jeep has this. Fine when cold, but low at idle. The bearing clearances are getting bigger with the mileage. So pressure drops, but flow increases. Since pressure gauges are cheaper than flow gauges, we go by PSI.

That said. I helped a kid swap over to a 400. Loss of oil pressure when he started to drive it. He pulled over and found that the white plastic line was burnt by exhaust. 5 minute fix, but what if it wasn't.

Check the easy stuff first before pulling the pan. What oil did you have? What oil did you put in?

[geeteeohguy]

10-12psi at idle is not dangerous. You need about 10psi per 1000 rpm. I would experiment with a different oil before I pulled the engine pan, but that's just me. 95psi cold is a ton of oil pressure, and would have me worried, personally, especially with a high volume (but not high pressure) pump. Early GTO's had about 60 psi max, and the later higher pressure 455 SD's, etc, ran an 80 psi pump.

[jonmachota78]

Scott, i had a similar problem when my motor had 900 miles in it. All of the sudden my oil pressure went down from where it had been. My problem turned out being a small piece of the morroso pickup broke free and stuck to the pump bypass ball preventing it from seating. Cold pressure wasnt too bad but was noticably lower than it had been, but hot pressure was way down especially at idle, it was less than 10lbs. I installed a test mechanical oil pressure guage by the dist to verify the readings and cut open the filter to inspect for debris. The low pressure was confirmed and the filter was clean. So pulled the motor, found the oil pump problem, replaced the pump, threw it all back together, pressure was restored, and now 10,000 miles later it's still good. I couldnt bring myself to do the cold rev thing like some guy do to flush out the bypass...
Im not saying that's your problem too, just sharing my experience. i would double check your pressure readings and cut your filter open for a look though. Good luck with it.

[scott-462]

For those that obviously didnt read my entire first post, it had 20 psi warm in gear at idle BEFORE i changed the oil and filter. Now with rotella diesel engine oil it has 10-12 psi warm in gear at idle. I cant remember the viscosity rating on the conventional oil that was in it before, but i think the ratings (10W-30?) are about the same if not the exact same between that oil and this rotella oil.. I just cant believe i lost 8-10 psi from changing oils?? Anyone else experience this?

[ponjohn]

What brand filter?

[PontGuy]

Yes different oils can give much different pressure readings. It would help to know exactly which oils you are talking about- viscosity ratings and whether conventional or synthetic. Also some of the zinc additives increase oil viscosity a good bit, so would be good to know what you are using for that too.

10 psi at idle will not hurt anything but I would select an oil that keeps idle pressure above 20. If it takes a heavy viscosity oil to get there or there is a sudden change in pressure using the same oil then there is a problem somewhere.

[mrennie]

While I have not experienced your issue before, I did want to comment on viscosity.

In comparing the 100*C viscosity numbers for various oils from different companies, I found that there can be a pretty big difference among oils with the same published grade.

My point is that the actual viscosity when at operating temperature way not be what you think it is, and it is possible that the new oil is thinner than what you took out. Most oil makers have technical information which will list the viscosity numbers at 40*C and 100*C, so if you can find this information for the old oil and compare it with the new stuff, this might give you some useful info.

Another thing you could try is changing the oil and filter back to what you had before, and see if the numbers return to what they were. Pretty cheap and easy test.

[screamingchief]

Originally Posted by ponjohn

What brand filter?

THIS ^^^^ ???

Hopefully not the 'ol orange can-O-death...

And FYI those 80 psi oil pumps can be hell on just about any OE spec pontiac oil filter.

If I were gonna run one of those 80 psi pumps myself,I'd wanna run something like a System 1 or another SS mesh oil fiter myself.

Bret P.

[scott-462]

I would have to find the box the filter came in or maybe check under the hood, but it wasnt a K+N or fram. The filter was white and your basic low buck filter. The first filter used was also your basic white low dollar filter, may have even been the same brand but i'm not sure.

[steve25]

You still have a problem Scott!
The fact is that if your pressure gauge is correct and you DO have 95 psi when cold, YOU SHOULD NEVER SEE LESS THAN 25 PSI WHEN HOT If you motors idle rpm is above 750 and the pump check ball is not unseaed due to some crap. even then if you where seing only 15 PSI of idle pressure, then when you apply a addition 1200 rpm to the motor the pressure sould JUMP right up to atleast 30 psi if all is well.

[screamingchief]

Remove the filter and cut it open,odds are pretty good the paper filter element inside has collapsed due to the higher pressure pump.

Like I said,those 80 psi pumps can be hell on OEM spec oil filters,especially when they're subjected to regular cold restarts where the pressure can spike over 100 psi @ times and the oil is thicker and more resistant to flow.

The internal bypass (be it in the adapter -or- the filter) should deal with that situation,but it's not unheard of that those can have problems too,and some disable the adapter bypass altogether (and some filters dont have an internal bypass),so that deal could come into play here as well,I really dunno for sure as so far that info has'nt been discussed just yet.

HTH

Bret P.