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Old 10-05-2012, 09:57 AM   #78
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Join Date: Sep 2012
Location: Old Greg's Cavern
Posts: 12,605
My Ride: '13 128i, '04 330Ci
Originally Posted by SeanC View Post
^Yep, we both got surprisingly low value for pressure at operating temperature. Makes the use of a 2-bar cap even more of a mystery in the e46. Even more so given that the e90's use only a 1-bar cap. Wonder what exactly is different between two systems.
I'm glad we have come to the same conclusion. I can think of no engineering justification for the 2 bar cap . I also don't think a 1 bar cap will help with the longevity of the ET. I think it WILL help prevent a headgasket failure in the event of an overheat, but in day to day operation, the system never runs over 1.4 bar and that is generous. I will continue to try to justify a 2 bar cap, but I don't think I ever will.

EDIT: I may try to calculate the temperature necessary to generate 3 bar pressure to trigger the 2 bar cap. I just got over 500C for an ideal gas, but at that temperature there will be lots of steam in the ET and the water will have expanded, reducing the air/steam volume. I'd have to reference one of my books for this, though I might have a matlab program for it.

Last edited by WDE46; 10-05-2012 at 10:02 AM.
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