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4040Re: [bmw e28] heat inquiry #2

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  • Blake Nancarrow
    Dec 11, 2005
      On Sun, 11 Dec 2005 19:35:49 -0800 (PST)
      Guy DiCesare <guydicesare2000@...> wrote:

      > My 88 535is has HOT heat while sitting still
      > which cools within seconds when I start driving. The
      > blower motor has made intermittent noise for years but
      > now the noise gets worse as I accelerate (but doesn't
      > seem to have any decrease in output though).

      Sounds like you have 2 problems!

      1. Thermostat? If the motor gets hot while you idle, then probably the
      thermostat is not opening or closing (whatever the case may be) properly.
      It should automatically regulate the flow of coolant through the
      radiator as needed. These little units are completely mechanical with
      bimetallic pieces. They "wear out" or the metal gets tired over time.
      It's a fairly easy DIY repair, but messy.

      You also need to check the main engine fan. As the clutch within the fan
      may not be working properly. But usually it's the opposite problem with
      the fan though: that the clutch seizes, so the fan always runs full
      blast, which makes the engine sound like a jet turbine! You can test
      this (with the engine OFF, of course) by spinning the main fan blades
      with your hand. It should not be very tight; neither, should the viscous
      coupling be completely free.

      Finally, you need to check the auxiliary fan and temperature sensors.
      But they usually only come into play in extremely hot situations, i.e.
      hot summer day, long highway drive, and then you slow down in
      stop-and-go traffic suddenly. Engines do not like that! All the heat is
      trapped in the motor. So the main fan with the assistance of the
      auxiliary are supposed to get rid of the excess heat. There are little
      electrical short circuit tests you can do, although I forget them off
      the top of my head.

      That the temp drops quickly suggests the water pump is OK and the flow
      through the cooling system is uninhibited and the radiator is not

      2. The cabin heater blower motor bushings or bearings wear out over time.
      It sounds like a squeaky hamster wheel for a while. Sooner or later the
      bearings will get so sloppy that the motor will shift and cage fans will
      start to rub against the shrouds. The extra friction may cause the motor
      to burn out.

      This is an awkward repair. But still definitely DIY. If you're inclined.

      Blake Nancarrow <blaken@...>
      (sent via Becky!)
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