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#3385974 - 05/31/14 11:57 PM Is my oil pressure gauge working properly?
ThirdeYe Offline


Registered: 02/23/07
Posts: 8114
Loc: Grand Rapids, MI
On my Firebird (3800 V6 Series II), I've noticed that the oil pressure gauge barely fluctuates at all. When the engine is completely cold, it's at about 70 psi. When fully warmed up, it's at about 60-65 psi. It doesn't seem to matter whether I'm at idle or if I'm on the highway going 70mph. I always thought at idle it should be much lower than that? I'm using an oversized Mobil 1 M1-201 on it, but I'm not sure if that would cause it to act like that or not. It's my first car with an oil pressure gauge, so I'm not sure what to expect. I can get it to fluctuate ever-so-slightly (in-line with the revs) if I'm accelerating... (maybe a 5 psi difference), but it eventually stabilizes right back to where it was. It's always between the 60-70psi range. Here is a picture of it at hot idle. It's covered up a bit, but the middle number on the gauge is "60"



Does that seem normal, or should I be concerned? I'm guessing the gauge is just a bit flaky, but I thought I'd ask here so as to not do any damage to the engine.
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#3385984 - 06/01/14 12:22 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
ZeeOSix Offline


Registered: 07/22/10
Posts: 15116
Loc: PNW
On my Vette, the oil pressure gauge goes from 30 psi at idle to about 70 psi at redline with hot oil (5W-30 @ 200 deg F).

It sounds like your oil pressure gauge isn't really very accurate. It should move over a larger range between idle and high RPM more than it seems too.

Also, a larger oil filter will not change the oil pressure you see on the gauge.

If you are on any chat boards that are Firebird specific, you might post there to see if other guys see the same reaction in their oil pressure gauge.

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#3386009 - 06/01/14 01:59 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
LvR Offline


Registered: 09/19/09
Posts: 18
Loc: SA
Long time lurker here

IMO it can be either.

Ideally, on a non-sludged and clean motor, I would like my oil pressure after the filter in the oil galleries to behave exactly like the OP's is ..................

In reality though no oil is perfect, no oil pressure regulating valve is perfect and oil pumps do wear (less output volume and thus pressure at lower revs), blocked/restricted galleries etc occur etc etc etc.

So depending on where (before or after the filter) the oil pressure is measured my guess is the meter may be 100% reflecting a very well designed lubrication management system of the meter is still working 100% .................... or possibly not

Only way to be 100% certain is to plumb another (known working and trusted) oil pressure meter into the same port via a T and compare readings.

Even if the meter turns out to be 100% in this case, I would wonder why this is in fact happening because I think most everybody owning even a fairly modern/current vehicle with oil pressure gauge on it is used to wide pressure reading fluctuations as a result of both temp and revs ............... iow is the constant pressure reflecting constant and good flow where one would expect it?

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#3386011 - 06/01/14 02:11 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
Olas Offline


Registered: 12/11/13
Posts: 3725
Loc: Manchester, England
Is it a proper gauge, in the true sense of the word?

A lot of 'gauges' these days are idiot-lights in disguise, they read normal or medium all the time unless theres an problem.
But there's also the chance that yours is a real gauge whicch has malfuctioned - as above you need a known working gauge on there to compare wink
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#3386052 - 06/01/14 06:14 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
Donald Offline


Registered: 03/21/04
Posts: 19345
Loc: Upstate NY
I think you need to try a mechanical test gauge to see what is going on.
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#3386053 - 06/01/14 06:14 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
Recalculating Offline


Registered: 08/04/12
Posts: 389
Loc: New York
I believe it is OK. I have changed the oil pressure sensor on my PAU when it continually read 130 psi over two years ago. Upon replacing, it displays digitally between 60 and 70 psi from start-up through warmed-up and running expressway.
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#3386058 - 06/01/14 06:29 AM Re: Is my oil pressure gauge working properly? [Re: Donald]
demarpaint Offline


Registered: 07/03/05
Posts: 28311
Loc: NY
Originally Posted By: Donald
I think you need to try a mechanical test gauge to see what is going on.


IMO that's the only way to know what's really going on.
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#3386066 - 06/01/14 06:48 AM Re: Is my oil pressure gauge working properly? [Re: demarpaint]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 18570
Loc: Sunny Florida
Originally Posted By: demarpaint
Originally Posted By: Donald
I think you need to try a mechanical test gauge to see what is going on.


IMO that's the only way to know what's really going on.


This. No gauge should ever be trusted until verified!
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#3386072 - 06/01/14 06:59 AM Re: Is my oil pressure gauge working properly? [Re: Olas]
fdcg27 Online   content


Registered: 09/25/09
Posts: 14503
Loc: OH
+1

Most gauges on newer cars are heavily damped, so that as long as oil pressure stays in a reasonable range, the needle hardly moves.
With a real oil pressure gauge, once the oil is warmed to operating temperature and thinned, oil pressure varies constantly with revs and engine load.
It may be that the dealers and the manufacturers got tired of people bringing back cars because they thought that something was wrong based upon the correct information given by the oil pressure gauge, so they set the gauge up to read a constant value when in reality oil pressure is only constant when the oil is cold and the relief valve is open or on a flat road at cruise.
Mercedes did it a little differently in that the oil pressure gauge is always pegged in normal operation and only comes off the peg at hot idle.
A clue here is that after warmup, I doubt that the OP's engine is really making 60-65 psi oil pressure.
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#3386076 - 06/01/14 07:04 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
Traction Offline


Registered: 06/04/13
Posts: 809
Loc: iowa
As already mentioned, it is probably not a real gauge. I have had a couple GM cars like that. It is only a needle connected to a resistor, and a oil pressure switch that would normally turn on a light a low pressure. They did this to give people a warm, fuzzy feeling thinking that their oil pressure was always okay. Too many complaints when someone saw the oil pressure was at idle 20 psi and thought something was wrong. It probably fluctuates some with voltage changes. When it always says 60 psi, everyone is happy.
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#3386084 - 06/01/14 07:23 AM Re: Is my oil pressure gauge working properly? [Re: Traction]
Charlie1935 Offline


Registered: 05/18/08
Posts: 628
Loc: DuQuoin, Illinois
If I'm not mistaken on todays vehicles the information gathered by all the sensors on engines is fed to the computer.
The computer then transmits the signals to the gauges.
As long as they are within a range that causes no problem you will see a feel good reading on the gauges.
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#3386107 - 06/01/14 08:09 AM Re: Is my oil pressure gauge working properly? [Re: Charlie1935]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 18570
Loc: Sunny Florida
Originally Posted By: Charlie1935
If I'm not mistaken on todays vehicles the information gathered by all the sensors on engines is fed to the computer.
The computer then transmits the signals to the gauges.
As long as they are within a range that causes no problem you will see a feel good reading on the gauges.


This is true, but only on certain makes. Not all modern cars 'censor' the sensor!

Far more likely that the oil pressure sending unit is failing or a bad ground is causing these symptoms...


Edited by SteveSRT8 (06/01/14 08:10 AM)
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#3386110 - 06/01/14 08:12 AM Re: Is my oil pressure gauge working properly? [Re: Traction]
RF Overlord Offline


Registered: 11/08/03
Posts: 3692
Loc: Cape Cod, MA
Originally Posted By: LvR
Only way to be 100% certain is to plumb another (known working and trusted) oil pressure meter into the same port via a T and compare readings.
This.
Originally Posted By: LvR
A lot of 'gauges' these days are idiot-lights in disguise, they read normal or medium all the time unless theres an problem.
And this.
Originally Posted By: fdcg27
It may be that the...manufacturers got tired of people bringing back cars because they thought that something was wrong based upon the correct information given by the oil pressure gauge, so they set the gauge up to read a constant value
Ford does exactly this.
Originally Posted By: Traction
They did this to give people a warm, fuzzy feeling thinking that their oil pressure was always okay. Too many complaints when someone saw the oil pressure was at idle 20 psi and thought something was wrong. It probably fluctuates some with voltage changes. When it always says 60 psi, everyone is happy.
Correct.

Having just agreed to all of the above, the OP gauge in my 2001 GMC Safari work van behaves like a real gauge. On cold start-up it can read 60, but when warmed up at idle will read about 25, and it freely fluctuates with RPM in between.
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#3386125 - 06/01/14 08:44 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
The_Eric Offline


Registered: 03/31/10
Posts: 5353
Loc: Iowa
Yes, in that vintage, GM was still making functional gauges. I believe they still do but cannot confirm.

At any rate 60 psi on a 3.8 is pretty typical of the ones that I've seen. Most would run just north of 60psi hot and idle in the high 30's/low 40's.

I'd verify with a gauge first if possible, then look into the sending unit or gauge in the dash.
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#3386171 - 06/01/14 10:04 AM Re: Is my oil pressure gauge working properly? [Re: ThirdeYe]
Virtuoso Offline


Registered: 02/25/03
Posts: 2703
Loc: Lincoln, NE
Our '01 Bonneville's pressure is around 35-40 when at hot idle, and ~60 at almost anything above idle.

Roughly 70 cold all over. That's if you trust my gauge.

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