I’ve just fitted a mechanical oil pressure gauge. On start-up, the gauge reads fine, about 70psi cold, needle reacts quickly and drops fairly steadily on key-off. What’s the verdict on bleeding the air out of the capillary line? I’m not sure it needs it, just wondered what anyone else had done and why? Thanks, Mat
No need to bleed, it would drain back anyway 
I don’t think it would drain back, as once the air has left it is under vacuum?
you will not gain anything noticable. but the change in pressure will be slightly faster to change as there will be less air in the line but there will still be air in the unit.
spend time doing it or spend time driving it.
i never have bothered bleeding any pressure gauge.
What vacuum? The oil circuit in an engine isnt Full vacuum. You can try to bleed it and see for yourself tho 
Think of it as sucking water into a straw and putting your finger over the end- the water stays in, until you let your finger off. Vacuum is probably the wrong word, more likely something to do with surface tension.
I’ve tried bleeding mine before but i found that it sucked air back out of the gauge into the pipe anyway so i just gave up and it works fine
I’ll leave it well alone then, thanks chaps!
It can be a messy process …
Totally, 100% unnecessary. Pressure is pressure be it in air or water. The compressibility of air will make the gauge respond SLIGHTLY slower on initial engine start. After the engine is started you will be VERY hard pressed to see any difference in response time.
Do not waste your time bleeding the line to an oil pressure gauge.
I only do it because when fitting a new pipe it takes no extra time, and if its a clear tube the air bubles look rubbish :lol:
Be very careful with those nylon oil pressure lines. They harden and become brittle with age. They also are easy to damage when working on the engine.
