Is it a sticky thermostat?
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1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Is it a sticky thermostat? in Past Cadillac Vehicle Discussion; I've got an 02 DHS with 81k. Had it since 78k. I replaced the coolant reservoir last year due to ...
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    Jesda's Avatar
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    Is it a sticky thermostat?

    I've got an 02 DHS with 81k. Had it since 78k. I replaced the coolant reservoir last year due to a false "COOLANT LEVEL LOW" error message.

    A couple weeks ago I noticed that in warm weather in heavy traffic, the temp needle will move one tick mark over to the right from the center. Since the coolant was very filthy I had a shop do a flush.

    The needle rarely moves past the center anymore and heater performance has improved. Unfortunately, it seems to take a little longer to warm up now, resting at one tick mark LEFT of center for much longer than usual before finally reaching the middle. Occasionally, in heavy traffic, the needle will still creep over to the right, but not as often as before.




    Is my thermostat stuck in a partially closed position?

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    MoistCabbage's Avatar
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    Yeah, if it's taking noticeably longer to reach normal operating temperature, it can't be much else.

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    Re: Is it a sticky thermostat?

    Dear Dr. Gulati,

    Please drop down to the Engines, Northstar forum and read the sticky threads on gauge operation, fan operation, and cooling system stuff. You might gain a bit of insight on why these heavily damped "gauges" read the way they do. Our thermostats are set to begin opening at 188 (about "12 o'clock") and be fully open at 206 - also at just about "12 o'clock".

    MAYBE, just maybe, a sticky thermostat - but that's a one-in-a-million chance for these cars.

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    Re: Is it a sticky thermostat?

    Generally speaking, thermostats are pretty reliable.

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    True, but nothing else would cause over cooling.

    The only other possibility I can think of is if it was heating up faster than normal before, and now it's taking longer, but heating up at a normal speed.

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    In heavy traffic, my thermostat gets to about 220. Once the fans kick on, it goes back to normal. But it still scares me.

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    Re: Is it a sticky thermostat?

    Perfectly normal. Designed that way.

    If you get worried when the temp gauge moves in response to engine operating conditions, turn the HVAC system ON and leave the A/C button ON. That way the fans run in SLOW any time the engine is running and the temp gauge should stay at about 12 o'clock.

    "Modern" car drivers go freako if a gauge needle actually moves - one big reason that many makes have done away with a good oil pressure gauge - too many false complaints when an owner sees the pressure go from 15 psi to 60 psi and back in normal city stop-and-go driving. Our temp gauges are so highly damped from 185 to 210 that they barely move a needle's width for the same reason.

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    I wasn't too worried because I took a 1100 mile road trip this weekend to Cape May and the car averaged 24mpg and on certain fill ups almost 27. The needle only moved when I got stock in Philidelphias rush hour.

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    Re: Is it a sticky thermostat?

    I'm not aware of these thermostats being particularly dependable. My 2001 STS had one replaced at 110k and it failed again at 140k, badly enough to throw a code and fail emissions.

    I always leave the climate system in fully automatic mode. What worries me about the heavily damped gauges on modern cars is that when the needle moves past the center at all, it's often a sign of trouble.

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    We very very rarely hear if these thermostats going bad. Not sure what code you got, was it for the engine not reaching operating temperature?

    It's perfectly normal for the gauge to rise a needles width or so above 12:00. Don't worry about that.

    What brand thermostat are you using, and are you using any kind of stop leak products?

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    Quote Originally Posted by Jesda View Post
    I've got an 02 DHS with 81k. Had it since 78k. I replaced the coolant reservoir last year due to a false "COOLANT LEVEL LOW" error message.

    A couple weeks ago I noticed that in warm weather in heavy traffic, the temp needle will move one tick mark over to the right from the center. Since the coolant was very filthy I had a shop do a flush.

    The needle rarely moves past the center anymore and heater performance has improved. Unfortunately, it seems to take a little longer to warm up now, resting at one tick mark LEFT of center for much longer than usual before finally reaching the middle. Occasionally, in heavy traffic, the needle will still creep over to the right, but not as often as before.

    Is my thermostat stuck in a partially closed position?
    In heavy traffic and idol in hot weather its normal for the temp gauge to move a click or so over and back to 12 center north stars run hot as is

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    Re: Is it a sticky thermostat?

    Quote Originally Posted by trailor View Post
    In heavy traffic, my thermostat gets to about 220. Once the fans kick on, it goes back to normal. But it still scares me.
    And that is exactly why GM dampened the gauges so much.

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    Maybe they should just put a sticker of a gauge at 12:00.....

    SGWORLDWIDE likes this.

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    Re: Is it a sticky thermostat?

    Quote Originally Posted by MoistCabbage View Post
    We very very rarely hear if these thermostats going bad. Not sure what code you got, was it for the engine not reaching operating temperature?

    It's perfectly normal for the gauge to rise a needles width or so above 12:00. Don't worry about that.

    What brand thermostat are you using, and are you using any kind of stop leak products?
    It was an error for failing to enter fuel system open loop or some nonsense. Issue was the thermostat. On road trips through cold climates, the needle would stay planted at one mark left of center, failing to reach full operating temperature, and in hot weather it would move one mark to the right and then slowly move back to center. T-stat was the fix, but it was strange to see the same issue on my Seville happening to this Deville.

    I always use OEM parts. No stop-leak junk, no tabs, no powders. Just green coolant 50/50 with distilled water.

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    Hmm. That is odd. Grab a Stant next time.

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