Erratic Oil Pressure Gauge

Erratic Oil Pressure Gauge

Postby Rich G. [OP] » November 26th 2012, 4:55pm

I've noticed my oil pressure gauge is rather erratic at idle after the engine warms up.

The dipstick indicates the oil level is full.

The pressure is steady during acceleration or when the oil is thick/engine is cold... or after a fresh oil change.

The engine seems to run fine. I don't notice any difference in RPM's/engine noises when the gauge is bouncing around.

Any thoughts on what might be causing this? Bad sensor? Bad pump?
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Re: Erratic Oil Pressure Gauge

Postby chevymaher » November 26th 2012, 5:42pm

They do that. Not the best gauges in the world. Check it with a mechanical gauge for peace of mind if you want.
Mine bounces in the 55 65 range but no where else. And like you said only when it warm. I checked mine it steady as a rock on a real gauge. As long as it not going to the red zone your good.
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Re: Erratic Oil Pressure Gauge

Postby sturoc » November 26th 2012, 6:40pm

I've seen this as well, usually when the oil gets thin due to hi temps or long drives ( like 4-8 hrs).
If engine is quiet, running fine and your temp is not abnormally high it's prob the sending unit/gauge just not reading right. As oil ages is gets thin and therefore pressure is lower.
I used to use that symptom as a 'get ready to change your oil soon' signal.

As chevym said the mech gauges are more true.
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Re: Erratic Oil Pressure Gauge

Postby Ragenme » November 26th 2012, 9:05pm

I've got a 98 and it jumps all over. sometimes and other times its fine.I want to replace it with a digital after market. Just need to find the correct app.
ragenme If you can't fix it with a hammer then its probably a electrical problem!
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Re: Erratic Oil Pressure Gauge

Postby Don1806 » November 26th 2012, 10:31pm

My 99 stil does it after changing the sending unit, and on both the old engine and a new remanufactured GM engine. Crappy gauge in the dash.
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New Engine at 140,000 miles due to intake gasket failure. Hoping to at least double that.
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Re: Erratic Oil Pressure Gauge

Postby chevymaher » November 27th 2012, 12:34am

My sending unit was bad reading low low pressure gauge worked fine. New sender and the pressure reads right but jumpy between 50-65 lbs. Good thing it runs 65 idle and 75 running. Except when it HOT then we got a measily 40-45 at idle. Piece of junk.
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Re: Erratic Oil Pressure Gauge

Postby MuRKRoW » November 27th 2012, 2:02am

65 to 75 lbs of pressure seems a bit high. What are you running for oil? 15W-40 with 2 quarts of Lucas oil stabilizer? Lol mine is around 55 at idle when I first start it, 70 when I'm driving and the engine is cold, 55 when the engine is hot and I'm driving, and 35-40 at idle when hot.

To answer the main question of the thread: Buy a new Oil Pressure Sending Unit. I accidentally broke mine off when I was changing my distributor cap/rotor about a year ago and I remember the sensor being really cheap and easy to replace. Good luck :dance:
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Re: Erratic Oil Pressure Gauge

Postby chevymaher » November 27th 2012, 2:22am

MuRKRoW wrote:65 to 75 lbs of pressure seems a bit high. What are you running for oil? 15W-40 with 2 quarts of Lucas oil stabilizer? Lol mine is around 55 at idle when I first start it, 70 when I'm driving and the engine is cold, 55 when the engine is hot and I'm driving, and 35-40 at idle when hot.


High volume oil pump with a 69 Z-28 302 High pressure relief spring.
And yes 15-40W synthetic. No lucas it don't need it.

I flogg it alot it needs the pressure. I have a oil pressure fetish. I tore up a few engines with low pressure over the years. 10 lbs per 1000 rpm rule.
When I get this thing straightened out computerwise. 6000 is the shift rpm with a 6500 red line. I got a few lbs margin for wear over the years.

Cold start up it at 75 lbs if I nail it before it warms up it runs 85 lbs a while.

I like old muscle cars. I know it my driver and a van.

But how does the sayin go?

You can take the boy out of the country.
But you can't take the country out of the boy.

:character-willie: :shrug:
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Re: Erratic Oil Pressure Gauge

Postby Rich G. [OP] » November 27th 2012, 6:29am

MuRKRoW wrote:To answer the main question of the thread: Buy a new Oil Pressure Sending Unit. I accidentally broke mine off when I was changing my distributor cap/rotor about a year ago and I remember the sensor being really cheap and easy to replace. Good luck :dance:


Thanks for the info! Can you point me to some instructions/photos on where the Oil Pressure Sending Unit is? I did some searches but came up empty.
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Re: Erratic Oil Pressure Gauge

Postby MuRKRoW » November 28th 2012, 4:07am

Rich G. wrote:Thanks for the info! Can you point me to some instructions/photos on where the Oil Pressure Sending Unit is? I did some searches but came up empty.


Look in my thread at the pics in the first post here: viewtopic.php?f=27&t=13141

The last and the 2nd to the last pics in the first post are of the oil pressure sending unit. It's right under the distributor cap/rotor assembly. If you take off the doghouse (the "inner" hood), then it will be directly in front of you at the back of the engine. It's hard to miss. If you can't find it, then take pics of that area on your engine and I'll point it out for you.
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Re: Erratic Oil Pressure Gauge

Postby Rich G. [OP] » November 28th 2012, 5:30am

Ok, got it. The pics really helped. I found some good YouTube videos about Doghouse removal as well (HERE's one). Since it appears this is not critical it may be a little while before I get to this project...
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