[GoGoat]

Added a mechanical oil pressure gauge to check factory gauge on my 66. New gauge read 90 to the pegged out factory at 60. After got it warmed up they read the same. Did the compressed air give me the high reading? Do I need to bleed the air out of my new line? Once bled will it stay bled? Thanks in advance.

[Goatracer1]

Everything seems ok. The original gauge just can't read high enough. 90 psig isn't uncommon when cold.

[Schurkey]

Originally Posted by GoGoat

Did the compressed air give me the high reading? Do I need to bleed the air out of my new line? Once bled will it stay bled?

Air in the plumbing will not change the pressure reading except during sudden transitions; and that's not all that important.

Air will creep back into the plumbing at every shut-down.

[lust4speed]

Yep, air compresses the same as oil and 90 PSI is 90 PSI. If anything air in the line will help smooth out sharp pulsations and settle the gauge down.

I will change the oil weight if there is too high of reading on startup. Swapping from 10W30 to 5W30 will drop start up pressure to a more sensible level.

[steve25]

Some folks need to go back and take a hydraulics review class in terms of there non correct thinking.

Air can be compressed, a liquid can not .

I

This is why when oil gets air mixed ( airated. ) in with it at some point you loose bearings if there’s enough air mixed in.

This is yet another reason why there needs to be a reserve level of oil in the pan.

It’s normal and especially at high rpm’s for small air bubbles to get in the oil .
These air bubbles take time to work there way up out of the reserve oil in the pan.

If this process is not given enough time then this oil infused with air gets pumped to bearings where it can not support the loads as needed.

The end result from this given enough time and or rpm is burned up bearings if your lucky, or a blown up motor if your not.

Many of a 100 percent perfectly built race motor with 7 to 9 Qts of oil in the pan have been lost to this issue, and even rebuilt only to fail again because of this difficult to diagnose issue.

Back to the gauge question.
Having air in your line feeding the pressure gauge will delay the gauge from reading changes in real time.

I have always purged my mechanical gauge of air right at the back of the gauge once the engine oil got some temp in it.

[lust4speed]

Your "real time" would be micro-seconds, and as Schurkey mentioned above all your hard effort will be in vain as air returns to the system. Shut the car off and oil drains back in the pan and is replaced by what? Air. It is purged out on start up but some will find its way back into the tubing.

[Dragncar]

If oil compressed our world would be vastly different as hydraulic systems could not work.
Purge the line to your gauge, if it makes you feel better. Does not do a thing.
Never done it and this last build the gauge jumped right up and pegged at 100 lbs.
The gauge would even come up cranking the engine over .
I work on hydraulic systems all the time with experts.
Never once have I seen anyone purge a line to a gauge.
And we are talking line pressures over 1500 lbs.
The Star Wars movies were filmed up here and the guy behind all the hydraulics on those things you seen was my boss.

[Schurkey]

Originally Posted by steve25

Air can be compressed, a liquid can not .

Mostly true. Liquids can be compressed but only by a couple percent. Not enough to affect hydraulic pressure transmission, and it's such a minor deal that most folks think they're entirely non-compressible.

Originally Posted by steve25

This is why when oil gets air mixed ( airated. ) in with it at some point you loose bearings if there’s enough air mixed in.

Also true...but this is a damn long way away from "I have an air bubble in the plumbing to my oil gauge."

Originally Posted by steve25

Back to the gauge question.
Having air in your line feeding the pressure gauge will delay the gauge from reading changes in real time.

I have always purged my mechanical gauge of air right at the back of the gauge once the engine oil got some temp in it.

The air in the plumbing to the gauge does nothing more than dampen the needle movement. Has no "real" effect on the gauge reading. And as long as the engine gets shut-off from time-to-time, and the oil drains back to the pan, you cannot prevent the oil gauge plumbing from also bleeding back, leading to air bubbles in the tubing over time.

[GoGoat]

Thanks everyone for their input. Original probelm was the factory gauge started dropping pressure (50 to 15) for different lengths of time. Then come back. I drove it an hour to a show, all the way there it read 15, all the way home 50. I've been thru 4 different sending units, all work for a short while. Now with machanical gauge oil pressure has stayed 100 percent steady while factory gauge drops once in a while. I just wanted to make sure check ball and spring wasn't the issue. My motor has been in car for 10 years. Thanks again.