Fan / coolant temp switch
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  • 1 Post By Submariner409
Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Fan / coolant temp switch in Past Cadillac Vehicle Discussion; Does anyone know where coolant/fan temp switch is located on a 1999 deville concourse ? Fan/s doesn't come on unless ...
  1. #1
    ffemt702 is offline Cadillac Owners Member
    Automobile(s): 1999 Deville Concours
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    Fan / coolant temp switch

    Does anyone know where coolant/fan temp switch is located on a 1999 deville concourse ? Fan/s doesn't come on unless Ac is on.

    Thanks
    ffemt702

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  3. #2
    rodnok01's Avatar
    rodnok01 is online now Cadillac Owners Connoisseur
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    Re: Fan /coolant temp switch

    Fans don't come on low even until @220 IIRC. What's your temp gauge reading?

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Fan /coolant temp switch

    Fans do not run in SLOW until coolant temp reaches 224 OR the HVAC is set to some function that calls for compressor operation. On your temp gauge that's about at the next mark after 12 o'clock (the center mark) and you won't see that unless you're stuck in really slow traffic. (Fans go to FAST at 236 degrees)

    The ECT sensor (Engine Coolant Temperature) is located down low on the right rear of the engine - just about in front of where your gas pedal toes would lie. The "switch" is the PCM. It receives system signals and controls the 3 fan relays in the underhood fuse box.

    Go to Engines, Northstar, and read the 3 sticky posts pertaining to cooling systems, fan operation, and gauge operation.

    Even if your gauge is sideways or a smaller sweep, the temp ticks are the same as this picture.
    ffemt702 likes this.

  5. #4
    ffemt702 is offline Cadillac Owners Member
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    Re: Fan /coolant temp switch

    Thanks Guys for response. Deville seems to over heat when at idle for a long time. Normal driving, the temp guage hits mid mark. I have changed the thermostat with a gm thermo stat and the antifreeze seems to be boiling. new thermo makes no difference, I wonder if the head gasket is gone. I just replaced water pump due to it leaking and and freeze disappearing.

    purchased a temp switch, but according to the post that may not be the issue.

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Fan / coolant temp switch

    A Northstar overheating - strike 1
    It's a '99 - strike 2

    Don't throw anymore parts at it until you do a block test.

  7. #6
    rodnok01's Avatar
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    Re: Fan / coolant temp switch

    Does sound like issue with fans then. if it keeps at good temp going down the road HG are prob fine. The engine prob finally burped and sucked the coolant in.

  8. #7
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Fan / coolant temp switch

    He never explained his definition of "overheating" at idle. If the gauge needle moves toward the first mark after 12 o'clock, that's perfectly normal in traffic or at idle.

    .......... and the ECT sensor is not a switch as such - this one is a variable resistor that allows changing voltage to be sensed by the gauge as the engine heats/cools and changes the resistance to ground.

  9. #8
    ffemt702 is offline Cadillac Owners Member
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    Re: Fan / coolant temp switch

    well, i have had the anti freeze checked for exhuast gases and the radiator shop started it wasnt a head gasket issue.

    let me explained overheating at idle. I can let the idle in the drive way, after 30-45 minutes the temp guage will go to the red zone. That means from the middle of guage on dash to H or red zone on the dash, the coolant sound like it's boiling after i shut it down. dash says engine over heated shuting off AC, change oil and thats all i could remember. I believe AC is on and both fans are running.

  10. #9
    basscatt's Avatar
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    Re: Fan / coolant temp switch

    replace the pressure cap -

    check the PURGE LINE -
    the PURGE LINE is the only way of expelling air from the Northstar cooling system -

    it is a 3/8 diameter hose that goes from a hollow bolt in the thermostat/waterpump housing area of the engine - and plugs onto a nipple on the side of the SERGE TANK -

    with the engine running - there should be a gentle - constant flow of coolant - from the engine - to the serge tank -

    if there is no flow - the most likely cause is a blockage in the hollow bolt -

    follow the hose towards the engine - with the engine OFF - remove the hose - use a straightened metal coat hanger - or something similar - and poke it into the hollow bolt -

    the coat hanger should go in about 2 1/2 inches -

    once the hollow bolt is cleared - you can briefly start the engine to verify coolant flow - be sure to use some sort of container to catch the coolant so you don't make a mess -

    check the hose and serge tank for blockage -

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