Re: Normal cold weather temperature fluctuation

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Re: Normal cold weather temperature fluctuation Posted by BobS (more from BobS) on Fri, 1 Jan 2010 13:01:54

In Reply to: WIS Specs...., Mark from Toronto, Thu, 31 Dec 2009 22:53:42 Members do not see ads below this line. - Help Keep This Site Online - Signup

Cold weather engine temperature fluctuation or cycling has occurred on every Saab I've owned since a 76 99. Typically it will stop when driving at > 45 MPH and/or running for longer periods of time. The engine has to get well warmed up for it to stop in very cold weather. It is not good for the engine to be shock cooled by ambient temperature coolant.
Your typical automotive tech is not concerned with such things, although the factory engineers should be concerned about it . You are on the right track about the heating times of the coolant in the engine and response of the thermostat. It takes very little coolant flow to keep the engine cool when the coolant entering the engine is <20 degrees.
With cold blooded cars, I have plugged the little hole in the thermostat to shorten (in one case by half) the time for the engine to reach thermostat temperature. Plugging the hole never caused a problem, although the thermostats in those days didn't seal that tight.
I wonder how well the little dangly thing in the Saab thermostat bypass holes really work. Supposedly they seal when coolant tries to pass, and unseal and allow gases through. Just how much coolant flow does it take to get the thing to seal?

posted by 71.221.22...

Posts in this Thread:

Lazy thermostat - is it hurting my engine?, Mark from Toronto, Tue, 29 Dec 2009 22:03:43
- Re: Lazy thermostat - is it hurting my engine?, TG, Wed, 30 Dec 2009 01:55:18
  - Is the fluctuation normal??, Mark from Toronto, Wed, 30 Dec 2009 12:34:20
  - Please explain??, bender , Wed, 30 Dec 2009 08:51:20
    - Re: Please explain??, SWEDECAR , Wed, 30 Dec 2009 08:59:34
      - and..., jeff in MD, Wed, 30 Dec 2009 09:29:57
        It's not really running that cold...., Mark from Toronto, Wed, 30 Dec 2009 10:17:20
        According to WIS specs for 4 cyl engines, TG, Wed, 30 Dec 2009 13:06:36
        Re: It's not really running that cold...., SWEDECAR , Wed, 30 Dec 2009 12:53:39
        Anders, you say something about fluctuating needle, bender , Thu, 31 Dec 2009 10:58:00
        Read down 3 lines....n/m, TG, Thu, 31 Dec 2009 12:02:07
        Something is not right here????????, TG, Wed, 30 Dec 2009 13:09:30
        Could be a case of too much info..., Mark from Toronto, Wed, 30 Dec 2009 14:08:16
        Re: Could be a case of too much info..., TG, Wed, 30 Dec 2009 15:04:54
        WIS Specs...., Mark from Toronto, Thu, 31 Dec 2009 22:53:42
        Re: Normal cold weather temperature fluctuation, BobS, Fri, 1 Jan 2010 13:01:54 <-- Viewing This Message
        Clarification here...., TG, Fri, 1 Jan 2010 13:36:18
        Needle does NOT fluctuate..., Mark from Toronto, Sat, 2 Jan 2010 10:06:35
        Re: Needle does NOT fluctuate..., TG, Sat, 2 Jan 2010 12:31:06
        Re: Needle does NOT fluctuate..., Mark from Toronto, Sat, 2 Jan 2010 15:17:42
        Simple answer, TG, Fri, 1 Jan 2010 08:38:27
        Re: Thermostat response, BobS, Wed, 30 Dec 2009 22:09:48
        Re: Thermostat response, Mark from Toronto, Wed, 30 Dec 2009 22:14:13
        At what engine temp does fuel mix go to stoich?, Mark from Toronto, Wed, 30 Dec 2009 14:16:12
        I think it's in WIS, TG, Wed, 30 Dec 2009 15:11:47

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