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    M42 heater problems

    Need some help regarding a weird problem that my 91 318i is having.

    Driving down the freeway, the heater blows cold, but when I exit the freeway, and start slowing down, the heater suddenly starts blowing warm. WTF,O? I know what you are thinking, it's nearly summer and you are complaining about your heater. Hey it's the SF Bay area, it only got up to the low 60's for a high today here so it's cold here in the morning.

    Any ideas of what my problem is (thermostat, air in the cooling system, etc...), please speak up.

    The engine was recently replaced in my 318i so the shop that did the work will fix it. The timing chain tensioner failed and snapped the timing chain with only 128K on the motor so replace your timing chain tensioner every 40K, that's my public service announcement.

    G-Man
    74 2002tii (many mods)
    86 325 (sold)
    88 325is (sold)
    89 325i (totaled)
    91 318is (parted out)
    91 318i
    98 Tacoma Prerunner (parts hauler)

    #2
    I would start by replacing the thermostat and flushing/bleeding the coolant system.
    Originally posted by Gruelius
    and i do not know what bugg brakes are.

    Comment


      #3
      There is also a heater valve under your dash that is known to get clogged so search for more info on the valve.

      1986 325es (69k) Garage Queen Buy It Now 10k;1986 325es (track rat) 2.7i How-To & 1.1/1.3Motronic UpGrade
      1991 318is (daily driver) 1991 318is M42 Maintenance How-To;1989 325i (parts car)

      Comment


        #4
        Does the temp gauge fluctuate hot to cold with driving speed?

        If no,

        Do this in order:
        Turn on your fan to high.
        Turn the heat all the way up.
        Turn off the fan.
        Do you hear a clunk?

        Change the order:

        Turn the heat all the way up.
        Turn the fan to high.
        Turn the heat all the way down.

        Does the heat dial stick?

        If no.

        Check that the hoses are on correctly...just swap them on the heater core.

        Let me know.

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