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Thread: Pressure Test - Cooling System - ? PSI

  1. #1
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
    119

    Default Pressure Test - Cooling System - ? PSI

    I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

    Thanks
    Jim
    90 535iA 141k
    90 735il 250k

  2. #2
    Join Date
    May 2004
    Location
    Windy City
    Posts
    606

    Default Correct psi is 30-45.

    Correct psi is 30 to 45. I usually max out at 50 to 55 psi (slightly overcharged). Make sure you don't put more than 70 psi! Also, make sure you check it with engine running and A/C on. Also, you must check it at low-pressure port which is the one that runs to A/C compressor.


    Quote Originally Posted by Jimmy535i
    I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

    Thanks
    Jim
    90 535iA 141k
    90 735il 250k
    RICK
    BMW 1995 525i (Alpine White)

  3. #3
    Join Date
    May 2004
    Location
    Japan
    Posts
    9,249

    Default

    Right expansion tank cap?
    Just check it, there was an exchange. I had my radiator 'exploded' by too high pressure.
    click here

  4. #4
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
    119

    Default Thank you shogun. I Have updated cap

    Quote Originally Posted by shogun
    Right expansion tank cap?
    Just check it, there was an exchange. I had my radiator 'exploded' by too high pressure.
    click here

  5. #5
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
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    Default

    Rick, Thank you. I will try 30-45 psi and listen for leak with engine off first.

  6. #6
    Join Date
    Jan 2004
    Posts
    4,150

    Default If you have the newest expansion tank cap, the one that was part of the recall then

    then it pops off and release pressure at 2 bars.... Bmw specs for testing pressure is 1 bar on the 735 or 14.5psi and 1.5 bars on the 750 or 21 psi..
    I would test it cold and then warm it up and test it warm... sometimes leaks that occur when cold don't show up when hot and vice versa.. When warming it up leave the expansion tank cap loose so it doesn't build up pressure





    Quote Originally Posted by Jimmy535i
    I have a slow leak somewhere in my cooling system on my 1990 735il. (250k miles). I want to run a system pressure test in order to find the leak and have borrowed the tool from my brother to do it. Anyone know what is the correct PSI to use for running this test? Any other advice would be great too.

    Thanks
    Jim
    90 535iA 141k
    90 735il 250k

  7. #7
    Join Date
    Jan 2004
    Posts
    4,150

    Default Jimmy don't put anywhere near 30-45 pounds that way too much and something will burst

    You're talking about the engine cooling system and Rick is talking about the air conditioning , 2 entirely different things.








    Quote Originally Posted by Jimmy535i
    Rick, Thank you. I will try 30-45 psi and listen for leak with engine off first.
    Last edited by Bill R.; 05-26-2004 at 10:50 AM.

  8. #8
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
    119

    Default

    Bill: Thank you for the information.

    I was talking about the cooling system. I was planning to test this weekend also.
    I replaced the upper radiator hose last year and the thermostat last week.
    I have a new water pump that I got from BMA - not installed yet.

    My AC sysem is fine. I converted it
    to R-134 2 years ago and it will freeze you out it is that cold.

  9. #9
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
    119

    Default

    735 - 1 Bar 14.5 psi - Thats the ticket - Thank you

  10. #10
    Join Date
    Jan 2004
    Location
    Northern, NJ
    Posts
    119

    Default Ran Pressure Test - Found Leak - Have ? (car hot)

    I ran the pressure test and found the source of my slight coolant loss.
    It turns out I needed to replace the hose from the thermostat housing to coolant reservoir. (it had a small crack) I ended up replacing a few other hoses and the system is now leak free. I replaced the thermostat also and bled the air from the system. The car ran fine for about 10 days (needle dead center) Yesterday when driving in slow traffic with the AC on the needle started moving above center again. (outside temp was about 90F)
    It looked like I was ready for an overheating episode. I pulled off and
    shut car off before temp went past 3/4.

    Could my waterpump be kaput ?
    Could my fan clutch be kaput ?

    I have both parts on my shelf. Got them from BMA.

    Any insight would be appreciated.

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