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Bad Temp Sensor? 850 1996

posted by  Stringer on  Mon Oct 15 07:18 CST 2007
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last visit: Fri Dec 17 04:53 CST 2010
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I am having problems starting the car as well as the fan runs at all times. There are posts that state that the temp sensor is bad but would a bad coolant temp sensor cause the motor to surge? The car can be cruising down the road and it will surge forward and I have to hit the brakes to control my speed. It happened even in park the engine would suddenly rev up to 3000rpm for a few seconds and then drop back down to idle again.








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    Bad Temp Sensor? 850 1996

    posted by  someone claiming to be ksg on  Mon Oct 15 10:14 CST 2007 [RELATED]

    The cooling fans are run by a temp sensor on the radiator, not by the ECT sensor on the engine block near the thermostat. So the fans running all the time seem to be a separate problem.

    It is not usual for the ECT sensor to go bad - tho the connections might be in poor condition. If the ECT sensor is not right the temp gauge on the dashboard won't read right either.

    I would try to resolve the issue of the fans - on some cars the fan operation is linked to control of idle speed. For instance if the system thinks the A/C is running and calls for the fans to run, then the fuel suppply at idle would be increased to overcome the extra load due to the compressor. You might get a surge if the a/c is not actually operating then - though it might be hard to detect while driving on highway.

    I assume you have no trouble codes set. Also have you ruled out all kinds of vacuum leaks, cracked air hoses, etc.?








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      Bad Temp Sensor? 850 1996

      posted by  will rehsper on  Tue Oct 16 01:00 CST 2007
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      last visit: Tue Jul 3 14:55 CST 2012
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      Your advice is good, but I'll still nit-pick. When the ECT sensor went south on our '94, the temp gauge pegged at the top and electric fan ran all the time. Driveability was not affected. Replacing the ECT sensor fixed both ailments.

      My point is that a faulty ECT sensor may cause the electric fan to run.

      -Will
      --
      850 / Mini








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        Bad Temp Sensor? 850 1996

        posted by  someone claiming to be ksg on  Tue Oct 16 02:44 CST 2007 [RELATED]

        You may well be right. I based my comment on a wiring diagram I downloaded for the 850 that seemed to match my own car. It's possible there were different configurations in different years, models, and markets, or even that there's more to the system than appears on my diagram.








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          Bad Temp Sensor? 850 1996

          posted by  will rehsper on  Tue Oct 16 04:46 CST 2007
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          last visit: Tue Jul 3 14:55 CST 2012
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          Agreed. Perhaps then I should have noted that my experience happened with a '94 base model, non-turbo, auto transmission car. Even though they are essentially the same car, there were many subtle differences under the hood of that car compared to my current 850, a '95 GLT non-turbo with manual transmission.

          -Will
          --
          850 / Mini







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