Pontiac V8 oil observation

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Feb 27, 2008
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Location
eastern WA
I have a 65 GTO with a fresh (1300 miles) 505 CID Pontiac V8 - aluminum heads, hydraulic roller cam, fairly mild - basically, the Pontiac equivalent of a ZZ502 or something along those lines.

I run Valvoline VR1 10w30 with a K&N filter. Cruise temps are 190. I observe the following:

If I go for a drive and just cruise, drive normally, the cruise oil pressure at 2500 RPM is about 45-50 PSI.
If I decide to beat on it a bit, a few full-throttle runs, the cruise oil pressure drops about 10 PSI.

I assume this is nothing to worry about, but I find it interesting and I don't quite understand it. Any ideas why?
 
Pressure is a bit low. Should be at least 10psi per 1k rpm (25 psi at 2500 rpm. Were the rod/main bearing clearances checked? Were the cam bearings checked? New oil pump?
 
Doh! Just re-read your post. Pressure DROPPED 10 psi not 10 psi. Engine heats up. Oil heats up. With stock oil pump, you are fine.
 
Originally Posted by ka9mnx
Pressure is a bit low. Should be at least 10psi per 1k rpm (25 psi at 2500 rpm. Were the rod/main bearing clearances checked? Were the cam bearings checked? New oil pump?


I mean it drops 10 PSI, from 45-50 at 2500 RPM cruise to 35-40 PSI at 2500 RPM cruise, or from 30 PSI idle to 20 PSI idle.

The whole engine is completely fresh, no used parts. Everything was checked by a local engine shop with a good reputation, but I don't have the measurements handy.
 
Yes, right - higher temp drops PSI. I get it, makes sense. But I find it odd that I've never noticed this before. I've spent plenty of time beating on the old engine and never noticed this, and I spend plenty of time beating on my 396 pickup and never noticed it either.

I have a guess, though. This engine still warms up REALLY quickly. Runtime temps are stable, but it comes up to temp really fast. So I think maybe it still needs to "loosen up" a bit. Perhaps oil temps and coolant temps both tend to rise quickly when you beat on on a fresh engine and this tapers off with some miles?
 
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When I drive my van on the highway the oil pressure slowly rises until I hit 60mph. North of 60 it will take a drop of around 10 psi. Probably the by pass valve working here on mine. At first it concerned me but then I realized even with the 10 psi drop, it had plenty of oil pressure (only vehicle I have with a mechanical pressure gauge).
 
The BB Chevy has a very good oil pump. If someone added a HV one to it pressure won't ever drop! The oil pump in the Pontiac can't quite move as much oil as the Chevy pump could.

Nothing to worry about. Enjoy your hot rod.
 
Originally Posted by Chris142
The BB Chevy has a very good oil pump. If someone added a HV one to it pressure won't ever drop! The oil pump in the Pontiac can't quite move as much oil as the Chevy pump could.

Nothing to worry about. Enjoy your hot rod.


Thanks, will do!
 
First thought is oil pickup too close to bottom of oil pan. Easy driving, no problem, stomp on it, the pickup is restricted and can't get the oil fast enough to the oil pump. Take it to the engine builder and ask/show them what is going on. That much of a oil pressure drop is not right.
 
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Originally Posted by oldhp
First thought is oil pickup too close to bottom of oil pan. Easy driving, no problem, stomp on it, the pickup is restricted and can't get the oil fast enough to the oil pump. Take it to the engine builder and ask/show them what is going on. That much of a oil pressure drop is not right.


I think there is a miscommunication. What I mean is this:

I am cruising at 2500 RPM, oil pressure is 50 PSI.
I beat on the car for a few full-throttle runs, oil pressure is at 60 PSI bypass pressure throughout the entire full-throttle runs.
I go back to cruising at 2500 RPM. Oil pressure is 40 PSI.
 
I had a 1966 GTO back in the day. That vintage Pontiac was notorious for poor oiling and not liking to rev very high because of hydraulic lifter float. Mine eventually threw a rod through the side of the block with no warning while cruising at 70 mph one afternoon. Your oil pressure drop is not at a dangerous level but I would run a heavier oil in it just to give you a margin of error. That thing must be a torque monster with over 500 cubic inches.
 
Originally Posted by CheezWhiz
Originally Posted by oldhp
First thought is oil pickup too close to bottom of oil pan. Easy driving, no problem, stomp on it, the pickup is restricted and can't get the oil fast enough to the oil pump. Take it to the engine builder and ask/show them what is going on. That much of a oil pressure drop is not right.


I think there is a miscommunication. What I mean is this:

I am cruising at 2500 RPM, oil pressure is 50 PSI.
I beat on the car for a few full-throttle runs, oil pressure is at 60 PSI bypass pressure throughout the entire full-throttle runs.
I go back to cruising at 2500 RPM. Oil pressure is 40 PSI.


Ya the oil heats up and gets thinner. Does the oil pressure go back to your cruise 50PSI after a while as it cool down? It should. Maybe run this info past the engine builder to be sure.
 
Thank you for powering your classic Pontiac with a Pontiac engine.
Cheviacs make me sick.

Pictures?

Maybe drain out half the oil, and replace it with 20w50 VR1. Then you'll have a 40-weight and can see if it helps oil pressure retention.
 
Originally Posted by CheezWhiz
I am cruising at 2500 RPM, oil pressure is 50 PSI.
I beat on the car for a few full-throttle runs, oil pressure is at 60 PSI bypass pressure throughout the entire full-throttle runs.
I go back to cruising at 2500 RPM. Oil pressure is 40 PSI.


Oil pressure is a function of oil temperature and rpm. Has nothing to do with "beating" on it. When cruising, temperature might be 200F. After beating it, 250F. 250F oil is thinner than 200F oil, hence the lower pressure.
 
I have, and have had, a number of 60's-70's V8 Pontiacs and have always used SW, VDO or Autometer mechanical gauges. These have all been stock, as from the factory engines, with various mileages. None of my cars would give me oil pressures as low as you are seeing. The easiest would be to rule out the gauge that you are using. If that checks out, I wonder if there is a valvetrain or piston oiling mod that was done to bleed off some pressure-that your builder should answer for you. Good luck.
 
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