Low Oil Pressure at Idle (Maybe) - Pontiac GTO Forum
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post #1 of 31 (permalink) Old 10-07-2019, 05:04 PM Thread Starter
 
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Low Oil Pressure at Idle (Maybe)

So I have recently noticed that my oil pressure on my 68 GTO seems to me, to be very low at idle. By very low I mean when the engine is totally warm, and I sit at idle for a minute, oil pressure can drop to 10 or even nine psi. This only happens when warm, at initial startup idle pressure is at about 40 psi. Idle when warm is at about 600-700 rpm. On the other hand, as I start to accelerate it climbs steadily and when Im at about 15 or 1800 RPM, I’m back up to 55 or 60 PSI. I’m trying to figure out if this is normal, or not. I am running 10 W 40, Brad Pen oil, and recently change my oil filter just for good measure. What do you Guys think? Any idea what would cause this, or is it even normal? The engine actually runs perfectly, knock on wood. Even at idle at nine psi, I hear no sign whatsoever of a tappet tick, of any sort or any other unusual sound - it idles perfectly. In fact when I open up a oil cap, I see plenty of green oil on rockers moving all over the place! Also no sign of oil leaks, no oil in water, and the oil level is not decreasing. Like I say, if I didn’t have a gauge, I wouldn’t even know about this to worry about it, maybe I should remove my gauge! :-)

I should’ve mentioned, my counsel is a Dakota digital, that was installed when the car was rebuilt a year or so ago. Again, I don’t know if this is new or not, possibly it is the first time I’ve noticed.
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post #2 of 31 (permalink) Old 10-07-2019, 06:26 PM
 
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Originally Posted by Ebartone View Post
So I have recently noticed that my oil pressure on my 68 GTO seems to me, to be very low at idle. By very low I mean when the engine is totally warm, and I sit at idle for a minute, oil pressure can drop to 10 or even nine psi. This only happens when warm, at initial startup idle pressure is at about 40 psi. Idle when warm is at about 600-700 rpm. On the other hand, as I start to accelerate it climbs steadily and when Im at about 15 or 1800 RPM, Iím back up to 55 or 60 PSI. Iím trying to figure out if this is normal, or not. I am running 10 W 40, Brad Pen oil, and recently change my oil filter just for good measure. What do you Guys think? Any idea what would cause this, or is it even normal? The engine actually runs perfectly, knock on wood. Even at idle at nine psi, I hear no sign whatsoever of a tappet tick, of any sort or any other unusual sound - it idles perfectly. In fact when I open up a oil cap, I see plenty of green oil on rockers moving all over the place! Also no sign of oil leaks, no oil in water, and the oil level is not decreasing. Like I say, if I didnít have a gauge, I wouldnít even know about this to worry about it, maybe I should remove my gauge! :-)

I shouldíve mentioned, my counsel is a Dakota digital, that was installed when the car was rebuilt a year or so ago. Again, I donít know if this is new or not, possibly it is the first time Iíve noticed.
I recently finished with the break in on my 67, also with new dakota gauges. Mine was not reading so I purchased a cheap gauge from the parts store. Like you mine seem to be oiling good but was glad to verify with another gauge that all is well. Finally corrected my dakota gauge. Verify with another gauge and if all is well check your gauges to be sure they are set up correctly. If you need instructions, let me know or you may find it on the web.
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post #3 of 31 (permalink) Old 10-08-2019, 06:50 AM Thread Starter
 
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I recently finished with the break in on my 67, also with new dakota gauges. Mine was not reading so I purchased a cheap gauge from the parts store. Like you mine seem to be oiling good but was glad to verify with another gauge that all is well. Finally corrected my dakota gauge. Verify with another gauge and if all is well check your gauges to be sure they are set up correctly. If you need instructions, let me know or you may find it on the web.
Thank you RMT, to make things a bit more complicated yet, I recall about a month ago sitting in a long, slow line for a cruise, when I was having definite engine overheating problems. I recall vaguely that I’ve noticed at that time my oil pressure was around the same low idle number. It seems though, that afterwards that was not happening, but now it seems like it’s happening again. I wonder if I cooked that sensor? I should mention that this car has Dougs headers, and these headers run fairly close to the sensor. I’m debating if I would be better off purchasing a new Dakota sensor and trying it, which would be an easy install, versus spending the money on a different gauge, and then coming back and buying a dakota sensor anyways? As I look at it, it’s probably indicating about 5 to 10 psi lower than I would expect across the spectrum. As I notice, it doesn’t look like it reads 60 anymore but maybe 55. When electronics fail, unfortunately they don’t always just die, I think it could be possible to get erroneous numbers. I think I’ll give it some thought.

Also googling around, I keep hearing about a 10psi per 1000 rpm rule, in general. So does that mean at a 700 rpm idle, 10 psi is fine? Like I said though, I'm not positive I believe the number is actually 10.

Thanks for your response.

Last edited by Ebartone; 10-08-2019 at 07:52 AM.
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post #4 of 31 (permalink) Old 10-08-2019, 08:30 AM
 
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Just install a manual pressure gauge (I believe you can even borrow from the parts stores) and test . My guess is it is either the gauge or the sending unit.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #5 of 31 (permalink) Old 10-08-2019, 09:14 AM Thread Starter
 
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Just install a manual pressure gauge (I believe you can even borrow from the parts stores) and test . My guess is it is either the gauge or the sending unit.
Thanks CIJ - I hate to show my ignorance, but can you tell me / link me to what you mean? As simple as an 1/8" NPT tube with a mechanical gauge on the end? Maybe just rout that up to the drivers compartment to watch it?

Ed
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post #6 of 31 (permalink) Old 10-08-2019, 09:29 AM
 
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Thanks CIJ - I hate to show my ignorance, but can you tell me / link me to what you mean? As simple as an 1/8" NPT tube with a mechanical gauge on the end? Maybe just rout that up to the drivers compartment to watch it?

Ed
Ed - Here is a link to a mechanical tester https://www.autozone.com/shop-and-ga...ressure-tester

You can find them anywhere auto related....

There are several ports you can use you read oil pressure depending on the motor and heads. Basically connect, run the motor and see what you are getting. (Obviously this is meant to be used while the car is stationary.)

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #7 of 31 (permalink) Old 10-08-2019, 09:55 AM Thread Starter
 
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Ed - Here is a link to a mechanical tester https://www.autozone.com/shop-and-ga...ressure-tester

You can find them anywhere auto related....

There are several ports you can use you read oil pressure depending on the motor and heads. Basically connect, run the motor and see what you are getting. (Obviously this is meant to be used while the car is stationary.)
Awesome CIJ, thank you - I'll find one and report back.....
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post #8 of 31 (permalink) Old 10-08-2019, 01:48 PM Thread Starter
 
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Ed - Here is a link to a mechanical tester https://www.autozone.com/shop-and-ga...ressure-tester

You can find them anywhere auto related....

There are several ports you can use you read oil pressure depending on the motor and heads. Basically connect, run the motor and see what you are getting. (Obviously this is meant to be used while the car is stationary.)
This guy seem legit?

https://www.amazon.com/Shankly-43503...1&rps=1&sr=8-2
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post #9 of 31 (permalink) Old 10-08-2019, 04:20 PM
 
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Or this https://www.harborfreight.com/engine...kit-62621.html

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #10 of 31 (permalink) Old 10-08-2019, 04:44 PM Thread Starter
 
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Better yet, thanks!
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