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Pontiac V8 oil observation #5196110 08/25/19 10:42 AM
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CheezWhiz Offline OP
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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?

Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196123 08/25/19 11:04 AM
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ka9mnx Offline
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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?


2005 Ranger 3.0 - SuperTech Syn 5w-30/Motorcraft
2000 4Runner 3.4 - SuperTech Syn 5w-30/Toyota
1997 B2500 Van 3.9 - M1 HM 10w-30/Mopar
1993 F150 4.9 - SuperTech Syn 5w-30/Motorcraft
Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196125 08/25/19 11:07 AM
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ka9mnx Offline
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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.


2005 Ranger 3.0 - SuperTech Syn 5w-30/Motorcraft
2000 4Runner 3.4 - SuperTech Syn 5w-30/Toyota
1997 B2500 Van 3.9 - M1 HM 10w-30/Mopar
1993 F150 4.9 - SuperTech Syn 5w-30/Motorcraft
Re: Pontiac V8 oil observation [Re: ka9mnx] #5196127 08/25/19 11:08 AM
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CheezWhiz Offline OP
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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.

Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196129 08/25/19 11:08 AM
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Chris142 Offline
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Oil gets hotter when you work it. Imo nothing to worry about but you can try a 10w40 or 20w50 to see what happens.


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Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196131 08/25/19 11:10 AM
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CheezWhiz Offline OP
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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?

Last edited by CheezWhiz; 08/25/19 11:14 AM.
Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196142 08/25/19 11:19 AM
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ka9mnx Offline
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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).


2005 Ranger 3.0 - SuperTech Syn 5w-30/Motorcraft
2000 4Runner 3.4 - SuperTech Syn 5w-30/Toyota
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1993 F150 4.9 - SuperTech Syn 5w-30/Motorcraft
Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196145 08/25/19 11:25 AM
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Chris142 Offline
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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.


02 Wrangler Napa high milage 10w40
87 F250 Valvoline 15w40
07 fjcruiser Car lube plus 10w30
Z400 castrol T 10w40
Can am Maveric edge 5w40
57 case tractor Chevron sae30
Re: Pontiac V8 oil observation [Re: Chris142] #5196147 08/25/19 11:28 AM
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CheezWhiz Offline OP
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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!

Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196148 08/25/19 11:28 AM
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oldhp Offline
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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.

Last edited by oldhp; 08/25/19 11:29 AM.

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Re: Pontiac V8 oil observation [Re: oldhp] #5196154 08/25/19 11:32 AM
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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.

Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196218 08/25/19 01:06 PM
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Always suspect pressure gauge and sender before anything else.


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Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196221 08/25/19 01:09 PM
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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.

Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196270 08/25/19 02:22 PM
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oldhp Offline
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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.


2018 RAM 1500 3.6/8 speed.
2019 Dodge Charger SXT 3.6/8 speed.
"When others cut you down, remember where they came from."
"I don't run...........I just wait"
Re: Pontiac V8 oil observation [Re: CheezWhiz] #5196284 08/25/19 02:44 PM
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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.


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