cooling nightmare continues

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  • 82eye
    E30 Mastermind
    • Jan 2009
    • 1841

    #1

    cooling nightmare continues

    ok, i'm getting to the end of my rope on this. every time i think i've got it handled the car screws up again. this thing just won't bleed correct and stay working without eventually getting too hot.

    symptoms :

    overheat. car will run normally for a time - days - then the temp begins creeping up. has gotten over the half mark to as hot as the 3/4 mark. has never gotten to red.

    leak. car will not leak when hot, but seems to lose a little coolant as it cools or sits when cold. haven't been able to find or trace the leak, it shows up in random spots under the car, on the passenger side of the engine opposite to the res. leak drops behind the rad but in front of the engine. no leaks from hoses under there.

    losing coolant. the res will drop about 1/3 to 1/2 when sitting cold but leaks very little to the ground. tested with cardboard under the car.

    res holds pressure even when cold.

    car blew return hose right off the therm housing once recently. has not done it again since.

    what has been replaced:

    everything except radiator and fan clutch. car has a bit under 2000 km on a rebuild. been trying to find the issue since it first fired up.
    all new hoses, new thermostat, new therm housing, new res, new cap, new heater core, new heater core o-rings, rebuilt water valve, new water pump and belt.

    what's been tested / looked at :

    compression and leakdown are good. no issues.
    no sign of coolant in oil or oil in the coolant. both changed multiple times to check. oil sample tested local with no contamination.
    head gasket combustion gas check in the coolant passes. combustion gas test liquid remains pristine blue.
    coolant system pressure test - seems to pass but the res adapter for the test sucks. only air we could find escaping was coming from the res itself. coolant does not escape from anywhere on a pressure test.
    fan clutch tests indicate clutch is good. shreds rolled up newspaper, does not stall fan out.

    what we are guessing :

    sticking or bad thermostat? these can be shitty from new now. no idea if it matches the symptoms.
    failing rad? rad seems to act normally and bleed correctly back to the res off overflow hose.
    bad / leaking or loosely installed water pump? what leak there is appears to be coming from the front of the engine, but does not account for amount missing in res.
    air lock? some kinda air lock that will not bleed out and does not affect the heater. heater returns hot air.

    has anyone have any ideas or had anything similar happen? i really sick of this over complicated cooling system that does not want to work.


    Last edited by 82eye; 10-10-2025, 11:15 AM.
  • It's Soda Not Pop
    E30 Modder
    • Jan 2022
    • 852

    #2
    Years ago I had an issue with my m20 overheating even after I replaced the water pump and bled, bled, bled, bled, bled, and bled some more. I just had to keep raising the front up and bleeding it. It eventually stopped overheating and starting acting right. That was the only time I had a huge problem. I have drained the coolant a multitude of times and I haven't had a very hard time since then. I always try and fill up everything with coolant that I can (fill voids where I can and then install) and have the front in the air as high I as I can.
    Check your clutch fan as well.

    88' Seta 2.7i Zinno

    https://www.r3vlimited.com/board/for...430-my-88-seta

    Comment

    • nadodude111
      E30 Addict
      • Jul 2009
      • 431

      #3
      You definitely have a leak somewhere. As the car cools down, there’s less pressure to push water against the hole and eventually gets to an equilibrium that allows air to enter in thru the hole. As air enters the system, coolant escapes and leaks onto the ground. This is causing you to have to bleed repeatedly to release the air that keeps coming in as the car cools down. Something says it’s the radiator.
      1992 325i Convertible

      Comment

      • TobyB
        R3V Elite
        • Oct 2011
        • 5158

        #4
        I forget- do you have an aftermarket temp gauge?

        I have fixed a couple of overheating problems with an accurate gauge...

        That said, if you're losing coolant, I too might be suspicious of the radiator.
        They're not E36 fragile, but the seals on the end tanks don't last forever...

        Also, in the for what it's worth category, I put a coolant pressure gauge on
        a car once, when I was having similarly frustrating problems. A turbo boost
        gauge works well. That helped me find a crack in a radiator neck...

        spitballing,
        t
        now, sometimes I just mess with people. It's more entertaining that way. george graves

        Comment

        • 82eye
          E30 Mastermind
          • Jan 2009
          • 1841

          #5
          thanks guys. pretty much any and all of the suggestions could be plausible.

          Comment

          • BadDays
            Member
            • Dec 2024
            • 55

            #6
            There might be a air leak coming from the radiator So I'd suggest checking it out to rule it out, On My Radiator, It was always letting air into the system before I'd figure out that there was some pinholes coupled with coolant leaking out of the bottom fins, that is what led to me throwing in a Chevy radiator in the first place.

            Comment

            • reelizmpro
              R3V OG
              • Dec 2003
              • 9446

              #7
              I went through the same thing with my S52 swap and replaced everything in the coolant system. After a while, it would always overheat expelling coolant out of the cap when it boiled over. I tested for combustion gases but since it was my first time I read the results wrong. I was looking for a dramatic change in color but since the blue fluid barely turned into a turquoise color...I thought it passed the test. A month later, another block test with fresh blue fluid showed even more of a color change and a shop confirmed it was indeed a bad head gasket. Perhaps it was just starting to go bad when I did the first test and got worse later. I would do another test before replacing a bunch of parts.
              "I'd probably take the E30 M3 in this case just because I love that little car, and how tanky that inline 6 is." - thecj

              85 323i M TECH 1 S52 - ALPINEWEISS/SCHWARZE
              88 M3 - LACHSSILBER/SCHWARZE
              89 M3 - ALPINEWEISS II/M TECH CLOTH-ALCANTARA
              91 M TECHNIC CABRIO TURBO - MACAOBLAU/M TECH CLOTH-LEATHER

              Comment

              • 82eye
                E30 Mastermind
                • Jan 2009
                • 1841

                #8
                Originally posted by reelizmpro
                I went through the same thing with my S52 swap and replaced everything in the coolant system. After a while, it would always overheat expelling coolant out of the cap when it boiled over. I tested for combustion gases but since it was my first time I read the results wrong. I was looking for a dramatic change in color but since the blue fluid barely turned into a turquoise color...I thought it passed the test. A month later, another block test with fresh blue fluid showed even more of a color change and a shop confirmed it was indeed a bad head gasket. Perhaps it was just starting to go bad when I did the first test and got worse later. I would do another test before replacing a bunch of parts.
                i'm thinking i'm gonna have to get a shop to look at it in the spring. we're getting snow this wk and driving season is over. not sure i'm gonna be able to work on it any more. i noticed it pushed a little coolant out of the cap. the head gasket test was pretty solid and we repeated it a couple times. zero change in colour, so i dunno where that leaves me.

                Comment

                • 82eye
                  E30 Mastermind
                  • Jan 2009
                  • 1841

                  #9
                  Originally posted by BadDays
                  There might be a air leak coming from the radiator So I'd suggest checking it out to rule it out, On My Radiator, It was always letting air into the system before I'd figure out that there was some pinholes coupled with coolant leaking out of the bottom fins, that is what led to me throwing in a Chevy radiator in the first place.

                  what leaking i see is also sort of pointing to the rad, but is inconclusive. probably need to get it tested at a shop to be definitive. i've fast run out of ideas to diagnose it.

                  Comment

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