In both the B201 and B202 motors, the coolant goes from the pump, through the block and head and then to the thermostat housing. From here it splits, with some going through the radiator (and then back to the pump) and some bypassing the radiator and going back to the pump. The weird thing about the Saab system is that the radiator bypass is THROUGH the heater core, or, should the heater valve be closed, through the heater control valve. You are right in that the T-stat does not have 3 fixed positions, and it continually modulates the percentages going through the radiator and through the heater control valve. In normal operation there is always flow through the heater control valve. However, the Saab T-stat is made with a little valve disc on the bottom that is meant to effectively seal off the bypass channel if the temp gets too high. All it really means is that the T-stat extends until the disc covers the return opening. In the B201 motor this meant no more flow to the heater control valve. In the B202 they created a small bypass that ensures limited flow even in overtemp cases. The reason to kill flow to the heater control valve in overheating situations is because if the heater control valve is closed, (as it would be on most hot summer days), the coolant bypassing the radiator does not go through the heater core at all, but instead goes right back to the pump. Also, even if the valve was open, there is much more heat transfer surface in the radiator, so the delta T across the radiator will be greater than that across the heater core.

posted by 68.14.134...

• over heating, bluetooth, Thu, 13 Feb 2003 02:58:58
  • Re: normal thermostat operation, JohnK, Thu, 13 Feb 2003 09:55:45
    • agree. 87C switch is available., Kevin K , Thu, 13 Feb 2003 12:12:16
    • Re: i dont believe that saab.., trog100, Thu, 13 Feb 2003 11:01:45
      • Go Trog!, Russell Giuliano, Thu, 13 Feb 2003 16:23:46
      • Re: that's the way it is, sorry, JohnK, Thu, 13 Feb 2003 11:40:38
        • Re: and its incredibly stupid in this case, trog100, Thu, 13 Feb 2003 13:13:43
          • Trog, I can Explain How and Why, Carl, Thu, 13 Feb 2003 23:43:27 <-- Viewing This Message
            • By the Way, Carl, Thu, 13 Feb 2003 23:51:12
          • not really, Kevin K , Thu, 13 Feb 2003 15:41:30
          • 2 things trog...., Chaz, Thu, 13 Feb 2003 14:49:13
            • Re: u are way off beam on that one chaz.. sorry, trog100, Fri, 14 Feb 2003 01:43:54
              • Trog, sometimes you say things when you are just wrong., Chaz, Fri, 14 Feb 2003 03:07:06
                • BTW-Trog, you removal of the t-stat test is not at load, Chaz, Fri, 14 Feb 2003 03:11:14
                  • PS - Trog, My post sounds angry, but I'm not....., Chaz, Fri, 14 Feb 2003 10:48:34
                  • Bottom line is..., Russell Giuliano, Fri, 14 Feb 2003 08:37:38
                    • LOL Russel ;-) n/m, Chaz, Fri, 14 Feb 2003 10:34:32
        • Replace my t-stat w/ one from Autozone..., joe w., Thu, 13 Feb 2003 12:42:06
  • Re: over heating, Dean M, Thu, 13 Feb 2003 07:31:16

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