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4041Re: [bmw e28] heat inquiry #2

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  • Ed MacVaugh
    Dec 11, 2005
      I don't agree.

      The hot at idle and none while underway are classic symptoms of the
      heater valve on the firewall having a split in its diaphragm.


      Blake Nancarrow wrote:

      >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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