Mechanical oil pressure gauge quandry

[KLF]

Posting this here 'cuz I can't find a better section. Installing an AutoMeter mechanical oil pressure gauge in my truck, with the upgraded copper tubing line. Question that occurred to me today: would the gauge be more accurate if I bled all the air out of the line before attaching it to the back of the gauge? Seems like the trapped air would not be a good thing, and have no way of escaping.

Edit: yes I fully understand the hydraulics and the pressure will be the same air or not. And I realize this is rather OCD.

 

[LAMBCRUSHER]

interesting...

 

[Tapage]

I never did in 3 mechanical gauge installation I did in 3 Cruisers.. ( non of those were Autometer gauge tho .. )

 

[FF LC FREAK]

would the gauge be more accurate if I bled all the air out of the line before attaching it to the back of the gauge? Seems like the trapped air would not be a good thing, and have no way of escaping.

Edit: yes I fully understand the hydraulics and the pressure will be the same air or not.

So, if the pressure is the same as you say, why would bleeding the air out make it more accurate?

 

[KLF]

I dunno. The question just occurred to me as I was preparing to hook up the line at the back of the gauge. Did some Google-ing, got mixed results. Sent an email off to AutoMeter Support, here's what I got back:

No, not at all. Even if you did, every time you would shut down the engine, the oil will drain back, thus trapping more air again on next start up. It is ok to use as-is.

Thank you
Cory
Tech/Service

Auto Meter Products
413 W Elm St.
Sycamore IL 60178
866-248-6357

I don't agree that it will drain back, as this would imply that air can get in from above at the gauge.

Heck with it, not gonna bother. It was just a thought...

 

[srgould41]

It is quite unlikely oil would drain back and let air up the line because of the vacuum created. For example, stick a straw under water and let the air out, then plug one end with a finger and lift it out of the water. If you hold the straw vertical the water will tend to stay in until you release your finger. It may happen, though. I use a larger diameter SS braided line which might make it easier for oil to drain down a little bit at a time and air to migrate up. The air would come from the block, not the top of the gauge.

I dunno. The question just occurred to me as I was preparing to hook up the line at the back of the gauge. Did some Google-ing, got mixed results. Sent an email off to AutoMeter Support, here's what I got back:



I don't agree that it will drain back, as this would imply that air can get in from above at the gauge.

Heck with it, not gonna bother. It was just a thought...

 

[KLF]

Well, it's plumbed and done. This hard copper line is a PITA. Even though it's only very thin 1/8" copper and bends easily, it's a pain to keep it from kinking when you are trying to snake it behind the dash and through the firewall. Next time I install this thing, I will go to the trouble to get a braided AN -2 or -3 hose made up.