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Coolant drip from back of block only when hot and not constant, no overheating

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    Coolant drip from back of block only when hot and not constant, no overheating

    Hey guys, '87 325i. Just did a fresh top end rebuild replacing literally everything. When coming home from work, my car has a coolant trip coming from the back of the motor. It seems to leak only when the car is warmed up and running. It doesn't leak while the car is sitting, except right after being shut off after a drive. The car doesn't overheat and I don't have coolant in my oil. The overflow reservoir level drops about a half an inch when I notice this happening. Everything is new including radiator, hoses, hose clamps, all gaskets including throttle body heater, my water pump is within its service interval, just had the head redone including a pressure test. Hose clamps are ALL super tight. It didn't leak coolant before being torn down. Freeze plugs look okay. The leak seems to be coming from behind the head where that metal hose is that connects to the heater core return hose. You can see coolant dripping down along the transmission where it connects to the motor, up top where the head mating surface is, but when I put my hand behind the head under that metal pipe to feel around for coolant, what I feel is a somewhat oily filmy kind of texture. Not clean but also not wet like coolant would be. I'm leaning toward that gasket being fucky but idk. Anyone have any advice?

    It not so much of a bitch for me to replace that since I redid my firewall insulation with thinner stuff and it's recently clean. I installed all that stuff about a year ago and have been working on suspension, rust repair, lots of other shit in the meantime so I don't remember but I don't think I used RTV on that seal. If I end up redoing it I think I'll put some on. Am I supposed to RTV it?

    Pic for encouragement
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    it's a Kenny Powers quote on wheels

    #2
    i usually use the permatex non hardening brown goop. it could be the surface on the head was corroded so not smooth enough for the gasket alone to work
    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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      #3
      Checked that rubber heater pipe that comes out of the back of head? mine developed a tiny pin hole in it in the weirdest spot. it too only leaked when hot.

      Best way to find it is get a coolant system pressure tester, and put it on the radiator and pressure it up and look for leak. This allows you to feel around with your hands when the engine is cold.

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        #4
        Wrap a small chunk of shop towel around the metal fitting, and drive it so it'll leak. Then try the same for the hose.

        And, heck, the head gasket join line, too, I guess, if both of the above stay dry.

        If they all stay dry, there are freeze plugs in terrible places that can do this...

        And yes, if that connection has some evidence of corrosion, I use RTV on it.

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

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          #5
          Thanks guys. To follow up I cranked down on the heater core hoses and the leak has seemed to disappear. Now onto the rough idle when cold condition...


          it's a Kenny Powers quote on wheels

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            #6
            80-90% of the time I find rough cold idle either the TPS being stuck in part throttle (idle side of switch broken), failing CTS (or signal via c191), or a vacuum leak post AFM.
            john@m20guru.com
            Links:
            Transaction feedback: Here, here and here. Thanks :D

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