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Topic Summary

Posted by: garage gnome
« on: April 08, 2013, 08:25:50 PM »

Yes, I would agree with Bob's explanation. Since the gauge is measuring PSI, the air will get compressed to the PSI that the oil is at, thus giving you the correct reading. Remember, you can compress air and not oil!  ;)  The same principle is used in a rotary screw compressor I believe.
Posted by: Bob W
« on: April 08, 2013, 08:15:07 PM »

The difference between brakes and the engine oil system is in the pump. The engine keeps pumping oil until the air in the oil pressure line is compressed and the gauge reads the actual oil pressure. When you step on the brakes there is only one single pump and then the pedal hits the floor. The air is never compressed enough to build the desired pressure in the brake system. Of course the pressure in the brakes is a lot higher than oil pressure, as mentioned.
Posted by: Pats4WD
« on: April 08, 2013, 07:43:59 PM »

Thanks for the feedback.  Mine seems to work fine also, no bleeding or mess.
Posted by: 1955CJ-5
« on: April 08, 2013, 12:17:26 PM »

Quote
I didn't bleed mine either...and it seems to work fine...but this is an interesting question. �If you think of it in terms of a brake system, why does it work without bleeding?

Things that make you go �"Hmmmm".

Tim

It must be the amount of pressure involved...in the oil line/gauge 40psi is max, as that is supposed to be where the oil pump relief valve opens, and the gauge will respond to 1 psi and up. An air bubble could probably carry that pressure though the reading would not be accurate. I bet you easily exert 40 pounds of pressure on the brake pedal with your foot, and this is magnified mechanically before it reaches the master cylinder, and then all that force is concentrated on a 1" piston..

Well, the service manual has a number...brake line pressure is 490psi with 100lb force on the pedal....fluids are not compressible, air is and so would absorb the pressure before it reached the wheel cylinder... that's why a brake system that needs to be bled feels spongy...

And just to remain on topic, I did bleed my oil line, but of course I have no idea if it made any difference, as it worked before I bled it.


Posted by: athawk11
« on: April 08, 2013, 11:46:44 AM »

I didn't bleed mine either...and it seems to work fine...but this is an interesting question.  If you think of it in terms of a brake system, why does it work without bleeding?

Things that make you go  "Hmmmm".

Tim
Posted by: bretto
« on: April 08, 2013, 06:58:11 AM »

I've read that some have don't that b4.  I didn't with mine and it works fine.
Posted by: garage gnome
« on: April 08, 2013, 05:52:03 AM »

I've never had to bleed them before.
Posted by: Pats4WD
« on: April 08, 2013, 12:51:13 AM »

All new gages are supposed to be arriving Monday.  Can anyone give me some insight as to whether the line to the the oil pressure guage needs to be bled like brake lines.  If so  do you just leave the line loose on the back of the gage and make giant mess under the dash?  I hope not.  Any help would be appreciated.

Thanks, Pat