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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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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.
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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Discussion Starter #3 (Edited)
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.
 

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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.
 

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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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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-garage-tools/oil-pressure-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.)
 

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Ed - Here is a link to a mechanical tester https://www.autozone.com/shop-and-garage-tools/oil-pressure-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-4350330500-Oil-Pressure-Gauge/dp/B07GYBWQC2/ref=sr_1_2?dd=y-bhwYSNeG789m9NkgWgTg,,&keywords=oil+pressure+tester&qid=1570560172&refinements=p_85:2470955011,p_90:8308921011,p_72:2661618011&rnid=2661617011&rps=1&sr=8-2
 

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You're doing the right thing verifying the accuracy of your gauge and getting a true pressure reading. My experience: the 10 psi per 1000 rpm is a valid value, that's all that's needed in these engines. Saying that, and having owned a few GTO's over the past 40 years, if your oil pressure really is 10 psi at idle and only goes up to 40-ish going down the road, that is on the low side. Normal pressures for these cars in stock condition are 20-30 psi at idle and 50-70 psi going down the road. The usual culprit for low oil pressure is increased bearing clearances due to normal wear. If it were me, and my car, and it wasn't making any strange noises, I would change the oil to a thicker viscosity and run it.
 

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You're doing the right thing verifying the accuracy of your gauge and getting a true pressure reading. My experience: the 10 psi per 1000 rpm is a valid value, that's all that's needed in these engines. Saying that, and having owned a few GTO's over the past 40 years, if your oil pressure really is 10 psi at idle and only goes up to 40-ish going down the road, that is on the low side. Normal pressures for these cars in stock condition are 20-30 psi at idle and 50-70 psi going down the road. The usual culprit for low oil pressure is increased bearing clearances due to normal wear. If it were me, and my car, and it wasn't making any strange noises, I would change the oil to a thicker viscosity and run it.
Thanks GTOG - Yea, this engine has been rebuilt within the last few years buy a previous owner (professionally), and as I mentioned, I've had no sign of any problems at all. From a number standpoint, per the current (Dakota Digital) gauge, when cold it will idle at about 40, then go up to 60 PSI no problem with very little additional rpm. When hot, I see this 9 psi thing when idling (at 700 or so), but it does go to 55-60 by about 2000 rpm or so when hot.

My concern was at idle being 9 or I saw 8 once, and it really makes no sense - I've heard engines with very low oil pressure before - the tappets talk to you! But no ticking whatsoever, or anything odd! Like mentioned before, about a month ago it did this low idle pressure thing, but then stopped and idle went back to 20 or so hot - but here I am again. Just seems odd.... With a little luck I'll try this tonight and see what happens.

Thanks!
 

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Discussion Starter #17 (Edited)
Well I have an update. I received my pressure gauge from Amazon today, and was excited to do this easy test. After all, my car has no air conditioning, and access to the oil filter and sender was pretty straightforward, except for dealing with the headers. My first challenge though was the sender that was already installed was incredibly tight. After a great deal of wrestling with it, I finally got the sender off, then installed the Male part of my gauge. After connecting at the gauge, happy as a lark, I went up, started the engine, and quickly ran around to take a look at what kind of pressure I was getting. What I got to see instead, was not what I expected! Oil was not just dripping from the area, but was squirting out at an incredible rate! It was unbelievable to me that I could have not tightened my adapter properly, or possibly the quick connect wasn’t working properly, but let me tell you that, you can drain the better part of 5 quarts of Brad pens finest within about five seconds at 60 PSI! After playing around, adjusting fittings, with the continued same problem, I eventually stole my wife’s mirror, looked around the back of the oil bracket, and, well you take a look at the picture - apparently my wrestling with the tight sender caused this. So now My simple Wednesday night project has turned into a catastrophe! I spent the next hour managing to get the bracket off, and will now shop for a new one! Not sure I remember what the original problem was anymore! :) I think I remember a post where someone was asking the question, why do I work on classic cars anyways!
 

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Well I have an update. I received my pressure gauge from Amazon today, and was excited to do this easy test. After all, my car has no air conditioning, and access to the oil filter and sender was pretty straightforward, except for dealing with the headers. My first challenge though was the sender that was already installed was incredibly tight. After a great deal of wrestling with it, I finally got the sender off, then installed the Male part of my gauge. After connecting at the gauge, happy as a lark, I went up, started the engine, and quickly ran around to take a look at what kind of pressure I was getting. What I got to see instead, was not what I expected! Oil was not just dripping from the area, but was squirting out at an incredible rate! It was unbelievable to me that I could have not tightened my adapter properly, or possibly the quick connect wasn’t working properly, but let me tell you that, you can drain the better part of 5 quarts of Brad pens finest within about five seconds at 60 PSI! After playing around, adjusting fittings, with the continued same problem, I eventually stole my wife’s mirror, looked around the back of the oil bracket, and, well you take a look at the picture - apparently my wrestling with the tight sender caused this. So now My simple Wednesday night project has turned into a catastrophe! I spent the next hour managing to get the bracket off, and will now shop for a new one! Not sure I remember what the original problem was anymore! :) I think I remember a post where someone was asking the question, why do I work on classic cars anyways!
Sounds like a quote I put up in april. "someone remind me why I am still working on old cars" lol:crazy: So far I am still at it. My new post "Timings off what gives" Well, when you get it back together, there is a plug near the distributor that you can tap into instead.I'm hoping your pressure (oil that is) will be ok and soon you will be past it all. Then it will be winter and unable to drive it ha ha.:(
 

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I am still in the breakin period with my rebuilt 400, Dakota digital gauges and dougs headers. My oil pressure is also about 60 at start up and when running, but also drops to about 20 at idle when a temperature. I have a 180 degree thermostat in the car and in Florida, in 90 degree temps, it runs about 185-190 degrees on the guage and on the het gun. I'm running Valvoline 10-40 racing oil. I wasn't too surprised the oil pressure dropped down when hot and idleing. Hope I'm not wrong to not worry.
 

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Well I have an update. I received my pressure gauge from Amazon today, and was excited to do this easy test. After all, my car has no air conditioning, and access to the oil filter and sender was pretty straightforward, except for dealing with the headers. My first challenge though was the sender that was already installed was incredibly tight. After a great deal of wrestling with it, I finally got the sender off, then installed the Male part of my gauge. After connecting at the gauge, happy as a lark, I went up, started the engine, and quickly ran around to take a look at what kind of pressure I was getting. What I got to see instead, was not what I expected! Oil was not just dripping from the area, but was squirting out at an incredible rate! It was unbelievable to me that I could have not tightened my adapter properly, or possibly the quick connect wasn’t working properly, but let me tell you that, you can drain the better part of 5 quarts of Brad pens finest within about five seconds at 60 PSI! After playing around, adjusting fittings, with the continued same problem, I eventually stole my wife’s mirror, looked around the back of the oil bracket, and, well you take a look at the picture - apparently my wrestling with the tight sender caused this. So now My simple Wednesday night project has turned into a catastrophe! I spent the next hour managing to get the bracket off, and will now shop for a new one! Not sure I remember what the original problem was anymore! :) I think I remember a post where someone was asking the question, why do I work on classic cars anyways!
Sorry .....You can find the filter housing easily (especially since you are in MI). Also the fitting near the distributor could be on very very tight, but I always like to test in both places.
 
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