oil pressure at idle?

[sam-131]

i dont know i carnt really be bothed with this engine i'll just ring its neck for a lil bit more and chuck the other motor in and check it out although i think allencr is on to something i dont know i'll soon see

[allencr]

Yes, air in the line doesn't matter at all, gauge pressure wise it is absolutely the same PSI reading. It's just that it will respond a little slower since it's being compressed, but is still much more responsive then an electric.

[takai]

Actually air compresses a lot more than oil, the reading which you get with air in the lines will be off, and can be massively off compared to no air.
Bleed the lines.

[love ke70]

but how does bleeding it work? because the oil drains back into the sump when you turn the car off....
and also, it compresses more because oil doesnt compress. but it should still read the same pressure shouldnt it?

[takai]

Nope, will read a drastically different pressure. And remember the oil will only drain back into the system when it can be replaced by air. In a small line such as the oil pressure line it will drain back, but only excruciatingly slowly as the oil becomes airated. Otherwise there would be a vacuum formed in the tip of the line/gauge.

It is why after sitting for several months/years you need to bleed lines again.

[love ke70]

sorry for being dense but how do you go about bleeding the line to the oil guage?
coz i cant see a way of doing it without pissing oil everywhere

[takai]

Guess what, you piss oil everywhere. Just hold a rag up against it, and then crank the engine with plugs out (and fuel off) until oil comes out the line, then just bolt it back up.