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Hot air at idle.... cold air at speed? WTF????

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    Hot air at idle.... cold air at speed? WTF????

    So I"m sitting at idle at a stop light and I switch the heat on just for shits and grins since I thought it was not working. Well to my suprise it works. STEAMY HOT AIR. I mean man I'm stoked cause its FRIGID outside. So I leave it on and take off..... within a few seconds of leaving the light the air is cold as tits. WTF is goin on? Antifreeze is full and car seems to be running at the proper temperature according to the gauge. Come to another light and its hot air again. Pull off and cold again. Yeah.... uhhh?



    #2
    Air pocket. Bleed the system a couple times and make sure its all good. Then check back with me. lol

    Will
    RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
    Welcome e30 (brilliantrot '90 325is) 12/23/06
    DaveCN = Old Man
    My signature picture was taken by ME! Not by anyone else!



    Originally posted by george graves
    If people keep quoting me in their sig, I'm going to burn this motherfucker down.

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      #3
      Its also possible that you have a stuck open thermostat. Does it take longer than normal to warm up?
      '91 318is
      sigpic

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        #4
        I was thinkin air pocket also. But wouldn't the air pocket rest at the front of the engine at speed?

        And no, it warms up like normal. Like I said it hits regular temp if not a little on the high side. It will idle for days at just shy of half staff.


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          #5
          So I bled it today and managed to strip the screw somehow. Needless to say it still does the same thing? Maybe I didn't bleed it all the way but I NEED heat mang.


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            #6
            Heater hoses COULD be a little clogged or something maybe... But I wouldnt go through the trouble in looking unless I knew that was it... I had symptoms opposite of that. Hot air when rolling, or with revved up, but not at idle. It was an air pocket. I dunno what else it could be. Sorry mang.

            Will
            RIP e30 (brilliantrot '91 325i) 11/17/06 Byebye: 8/21/07
            Welcome e30 (brilliantrot '90 325is) 12/23/06
            DaveCN = Old Man
            My signature picture was taken by ME! Not by anyone else!



            Originally posted by george graves
            If people keep quoting me in their sig, I'm going to burn this motherfucker down.

            Comment


              #7
              Have you had the heater pipes off on the bulkhead ?

              If they are put back on the wrong way around they give a very similar problem to what you are describing.

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                #8
                Thats what euro3 was telling me. That there's a magnetic switch that closes off the lines if there's too much pressure. Yada yada. I haven't had them off, but that doesn't mean the PO didn't. So we'll see what happens when I find a large field near some wildlife and switch the lines around.


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                  #9
                  When your car is warmed up is the temp gauge in the middle?

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                    #10
                    Just shy of it. I'd call it 7/16th of the gauge.... not half.


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                      #11
                      Well from the handy dandy Bentley:
                      Low heater output could be cause by a faulty heater valve, mis adjusted blending flap cable (one of the controls) or a cooling system fault.

                      It sounds like your cooling system is operating normal. Do you ever smell anti-freeze or get super fogged up windows? If not Id be going for the valve and control cables.

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                        #12
                        It ended up being a set of reversed lines to the heater core. I guess one of the PO's had reversed them. This problem was accompanied by a "ticking" that came from under the dash at low rpm that I attributed to a faulty tach gauge. In all actuality this was the pressure switch shutting the valve to the heater core. Thus after a few seconds of air blowing accross the heater core, it went cold. At idle the valve would return to normal due to the lowered pressure and would supply new hot coolant to the core and thus the hot air again. A 5 minute fix (would have been 2 without a strut bar in the way) and now my toes are toasty warm. On to the next project :D


                        Comment


                          #13
                          Originally posted by marakka
                          It ended up being a set of reversed lines to the heater core. I guess one of the PO's had reversed them. This problem was accompanied by a "ticking" that came from under the dash at low rpm that I attributed to a faulty tach gauge. In all actuality this was the pressure switch shutting the valve to the heater core. Thus after a few seconds of air blowing accross the heater core, it went cold. At idle the valve would return to normal due to the lowered pressure and would supply new hot coolant to the core and thus the hot air again. A 5 minute fix (would have been 2 without a strut bar in the way) and now my toes are toasty warm. On to the next project :D

                          What i said then

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                            #14
                            glad i found this thread, have the exact same thing happening to my car. sweet. Was it easy to switch them around or did you get coolant everywhere?

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