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Thread: No cabin heating at fwy speed

  1. #1
    Join Date
    Oct 2006
    Location
    Montgomery, AL
    Posts
    13

    Default No cabin heating at fwy speed

    Hi,
    I have a problem with cabin heater.
    The engine warms up quickly after start, stays at the right temperature, no overheating problem at all. Cabin heating works if I’m driving slowly in city traffic but the hot air cools down if I’m driving 70-80mhp.
    Last time I drove 30-40 min. in a freeway not having heating at all. Close to the office at the stop light while I was standing it started blow the hot air.
    If I’m moving fast I have no heating, if I’m driving slow I have hot air.
    I might be important that I have replaced the radiator in the beginning of the summer, but I haven’t used the heating on freeway, just in slow traffic where it is fine.
    The car is ’95 530i, M60 engine.

    Thanks
    Zoltan

  2. #2
    Join Date
    Jul 2006
    Location
    Albany, NY
    Posts
    451

    Default

    Sounds like your thermostat is stuck open.

  3. #3
    Join Date
    Oct 2006
    Location
    Montgomery, AL
    Posts
    13

    Default

    Quote Originally Posted by brosher
    Sounds like your thermostat is stuck open.
    Well, regardless of ambient temperature the engine warms up quickly within 3-4min. Once it is warm it stays right on temperature, as it should be.
    The cabin heater blows cold on highway speed only, if I slow down it warms up, than at 70-80mph the air cools down again, but does not effect the engine temp.
    Why do you think it is thermostat?

    Thanks
    zoltan
    Zoli
    530i/5speed

  4. #4
    Join Date
    Oct 2004
    Location
    Honolulu
    Posts
    3,105

    Default Check the aux pump

    under the heater valves.

    It may not be working


    Vee ave vays of dealing vid your kind...........

  5. #5
    Join Date
    Dec 2003
    Location
    Eastern Tennessee USi
    Posts
    14,839

    Default

    because thats a tell tale sympton of a bad stat.
    Quote Originally Posted by bzoli
    Why do you think it is thermostat?

    Thanks
    zoltan
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  6. #6
    Join Date
    Jan 2005
    Location
    Melbourne Australia
    Posts
    326

    Default

    try the air on recycle setting too, may help in the short term?
    1994 540i Auto

    live fast; die sideways
    13.3 @ 104mph (not in the 540)
    15.4 @ 150 Kph in the 540 (24/9/07)

  7. #7
    Join Date
    Dec 2005
    Location
    Mt. Vernon Ohio
    Posts
    260

    Default

    I assume at 80mph your coolant is being cooled a bit better than at say, 25? </3
    1993 525iA M50TU
    Black on Black...need pics
    208,888 miles

  8. #8
    Join Date
    Jan 2006
    Location
    Nashville, TN
    Posts
    249

    Default

    Although these cars are supposed to be self bleeding, if you park downhill you may have gotten an air bubble in the heater core. More likely is that your heater valve has/had some crap in it. My heat went out coming back from Atlanta last Feb just as I crossed Monteagle in a foot of snow. I will find out which when I rebuild the cooling system next week (before it gets cold again).
    Last edited by zhandax; 10-14-2006 at 04:00 PM. Reason: spelllink
    The stone age didn't end for a lack of stones. Neither will the hydrocarbon age......

  9. #9
    Join Date
    Oct 2006
    Location
    Montgomery, AL
    Posts
    13

    Default

    Quote Originally Posted by NovceGuru
    I assume at 80mph your coolant is being cooled a bit better than at say, 25? </3
    Today in the morning the ambient temp. was 43degF (6degC - yeah its getting cold), engine coolant temp stared rising less than a minute, and fully warmed up to operational temperature within 4 min.

    If I go the highway there is not coolant temperate drop (as far as I can see from the temp gauge) just because I drive fast and more coolant air is available.

    How much coolant temp. drop do you expect at 80mph if the thermostat would stuck open?


    thanks for the response!
    Zoli
    530i/5speed

  10. #10
    Join Date
    Jul 2006
    Location
    Albany, NY
    Posts
    451

    Default

    Well you can't entirley trust the gauge as it's not very accurate. There are no numbers or scale. I think it's just there to show impending doom.

    What happens with a stat that is stuck open is coolant keeps flowing over the radiator no matter what temp it is at. Around town there isn't enough air flowing over the radiator to make a differance in temp and the stat would prob be open anyways. When you get on the highway the stat should close to keep the engine and coolant at operating temp. If it stays open then the coolant will continue to be cooled below the desired temperature, ussually 85C.

    Your heater works by blowing air over the heater core which is basically a small radiator. If the coolant temp lowers enough from the above scenario than the heater core will not get hot and you have no hot air. When you get off the highway there is no longer air flowing at a high rate over your radiator so the coolant and heater core warms up again.

    On most cars you could look into the open radiator cap. If you saw coolant flowing right away than your stat is stuck open. I don't know if there is any way to verify on the M60 in such a way. It's $30 for the stat and a new O ring, I'd start there.

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