# 69 GTO oil pressure problem



## trainman115 (Jul 31, 2014)

Hi Everyone wondering if someone can help me out I have a 69 gto with gauges when i discount the wire from the unit the gauge goes up when I ground the wire the gauge goes to zero when I put the wire back on the unit start the car up take it for a ride its fine until it gets hot I am guessing then it goes almost up to 80 just sitting the gauge is about half way then when I shut the car off the gauge wont go all the way up stays some apass the first line I have change 3 units already 80 pound units I even tried grounding the unit itself doesnt matter does nothing to the gauge again take wire off unit put it back on seems to go to zero maybe the first line would by chance the heavier oil would cause this or am I getting junk NAPA units any help will greatly Appreciated


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## Old Man Taylor (May 9, 2011)

It sounds like that's just the idiosyncrasies of the gauge. Does it make any engine noise while driving it?


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## BLK69JUDGE (Jun 10, 2010)

at rest "I" find on my rally gauges key off
that they ALL 3 sit at 1/4 +- a needle or 2 usually +

then turn the key on ,,,,, fuel gauge should move

oil drops to 0

water temp to zero


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## trainman115 (Jul 31, 2014)

Old Man Taylor said:


> It sounds like that's just the idiosyncrasies of the gauge. Does it make any engine noise while driving it?


engine noise?? the gauge ?? no


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## trainman115 (Jul 31, 2014)

BLK69JUDGE said:


> at rest "I" find on my rally gauges key off
> that they ALL 3 sit at 1/4 +- a needle or 2 usually +
> 
> then turn the key on ,,,,, fuel gauge should move
> ...


Thats my trouble when I shut the key off and then turn it back on my oil pressure is up about line and 1/4 when I discount the plug and put it back on it goes to zero


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## Old Man Taylor (May 9, 2011)

trainman115 said:


> engine noise?? the gauge ?? no


The purpose of the question was that if your oil pressure was actually low while running you would damage your engine. If it is not low while running, and the gauge shows the correct pressure while running, then what your seeing is just an idiosyncrasy of the gauge. Why not put in an analog gauge instead of an electric one?


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## Mine'sa66 (Oct 30, 2019)

You could just buy a cheap analog gauge and temporarily hook it up right under the hood. See what your oil pressure is for real and then you won't be guessing. I'm living dash wiring issues myself. Sounds like you may have ground issues in the cluster. Do your dash lights operate correctly?


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## trainman115 (Jul 31, 2014)

Mine'sa66 said:


> You could just buy a cheap analog gauge and temporarily hook it up right under the hood. See what your oil pressure is for real and then you won't be guessing. I'm living dash wiring issues myself. Sounds like you may have ground issues in the cluster. Do your dash lights operate correctly?


yes everything works as it should want to keep original if possible


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## Mine'sa66 (Oct 30, 2019)

trainman115 said:


> yes everything works as it should want to keep original if possible


My suggestion of hooking up an analog gauge was to just do it temporarily. This way you'll know what your actual oil pressure is. Then you can determine if your factory gauge is accurate or not.
An old fashioned analog oil pressure gauge is literally a small tube going from the engine to the gauge. They don't need power (except for lights), so you could just stick the pickup in the factory hole, run the hose over to the gauge, then run the engine and see in real time what your oil pressure is. 
If you wanted to drive it around a bit, just run that little hose through an existing opening in the firewall to the gauge. You can just leave the gauge sitting beside you while you see what the oil pressure is under differing circumstances. If the analog agrees with your factory, then you know you've got a actual pressure issue. If not, you know you need to further diagnose the sensor circuit.


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## Lemans guy (Oct 14, 2014)

Exactly! Solid advice, and there are two places an oil pressure gauge can fit one at the filter location and one just to the left of the distributor.

I actually run two oil pressure gauges, both electric and both have idiot lights high and low as well. Just convenience really, if a gauge reads an oil pressure drop is it no pressure or a bad sender or bad gauge?

with two I can just read the other one if it is good I know the sender or gauge is malfunctioning and don’t have to stop and get a tow. I can just read the other gauge.

if both drop then I know I lost oil pressure......


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## trainman115 (Jul 31, 2014)

Mine'sa66 said:


> My suggestion of hooking up an analog gauge was to just do it temporarily. This way you'll know what your actual oil pressure is. Then you can determine if your factory gauge is accurate or not.
> An old fashioned analog oil pressure gauge is literally a small tube going from the engine to the gauge. They don't need power (except for lights), so you could just stick the pickup in the factory hole, run the hose over to the gauge, then run the engine and see in real time what your oil pressure is.
> If you wanted to drive it around a bit, just run that little hose through an existing opening in the firewall to the gauge. You can just leave the gauge sitting beside you while you see what the oil pressure is under differing circumstances. If the analog agrees with your factory, then you know you've got a actual pressure issue. If not, you know you need to further diagnose the sensor circuit.


Thanks for the info I did a change over from idiot lights to gauges I thought I might have done something wrong I did change the two wire that I need to for the circuit board according to the wire diagram all works as should except the oil pressure again I tested the gauge seems ok when I pull the plug off the unit it goes to 80 ground the wire goes to 0 so thats telling me gauge ok start the car go for a ride everything ok so as it gets hot or ran awhile the gauge goes up to almost 80 which I know is wrong seems to me its losing ground some how when hot I shut the key off and just turn it back on the gauge wont go back to 0 it stays maybe at 20 I think it should go back to 0 I have no clue wanted to keep it with rally gauges but it looks like that aint going to happen I will go with a analog gauge I guess and call it a day Thanks for everyone who tried to help me


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## PontiacJim (Dec 29, 2012)

The sending unit and gauge should be sent out to someone who can test/calibrate them together as a pair. Because the oil pressure gauge works, does not mean it is calibrated to the sending unit. Many of the aftermarket sending units don't calibrate correctly with factory gauges.

Second, the oil sending unit down at the filter housing needs to be installed with no sealant on the threads. The sending unit uses pipe threads to tighten and seal. If you put sealant on the threads thinking it is the right thing to do so no oil will seep/leak out, then you may not get the required/good ground that the sender needs to provide an accurate reading.

Also make sure you have all your ground straps on the engine/body as when an engine is pulled or restoration done, the ground straps have a tendency to be left off and can create a number of problems with electrical components.

You also want to make sure you have the required ground straps on the gauge/dash panel The panel is plastic and there are ground straps needed for the gauges to work correctly.


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## mikelly2 (Nov 24, 2018)

I'm late to the party as usual. I agree with minesa66 except I wouldn't use a cheap mechanical gauge. I would use one that I new was accurate. I'm partial to Autometer myself but there are others.

Also just wanted to say that this forum is fortunate to have Pontiac Jim. I seem to learn something every time he posts.


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## O52 (Jan 27, 2019)

I talked to Peter Serio the other day regarding the rebuild of my Rally Gauges. According to Peter the gauge coils were wrapped with an epoxy and never intended to last 40 or 50 years. The epoxy breaks down and erratic gauge operation is the result. He also stated that the oil pressure sending units have a small hole in the housing to allow the diaphragm to operate. This can allow the inside of the housing to corrode under the right conditions and prevent smooth operation of the diaphragm.


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## trainman115 (Jul 31, 2014)

I took apart the big cover off a new oil pressure gauge grounded the unit and put my wire on turn the key on the needle fell to 0 I slowly moved the arm up and the gauge read as it should so I think thats telling me gauge and unit are ok I think but does not tell me y it acts up when hot again shut car off and just turn key on gauge wont go to zero no one can figure this out I am just going to put the idiot lights back in and get a set of gauges the hell with the rally gauges LOL Thanks again guys for trying to help


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## Mine'sa66 (Oct 30, 2019)

mikelly2 said:


> I'm late to the party as usual. I agree with minesa66 except I wouldn't use a cheap mechanical gauge. I would use one that I new was accurate. I'm partial to Autometer myself but there are others.
> 
> Also just wanted to say that this forum is fortunate to have Pontiac Jim. I seem to learn something every time he posts.


I would never install a cheap gauge permanently. In this case though, low end oil pressure gauges are the way to go as it is a direct measurement. Just like a vacuum gauge, there's a mechanical tube from engine to gauge. A higher end sending unit type gauge is much more reliable, but it still introduces the aspect of it's not a direct measurement, and you're going to have to wire it to make it work and the whole deal was supposed to be temporary.
What I would do since I do it for a living and have the tool, is hook up a universal pressure gauge that is used for testing pressures in all sorts of things.
Since most don't have that handy, a "cheap" mechanical oil pressure gauge is a great substitute.


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