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Thread: Fan clutch ?

  1. #1

    Default Fan clutch ?

    Hi all,

    Been having a problem with my '99 7.4 (big block) running too cold, usually well below 180. This seems to cause the 'burb to get worse mpg than it should. It was suggested I swap out the t'stat to a 195, so I just did, no change. In talking to a mechanic (pro) I know we noticed the air behind the fan was cold, really cold. Then we noticed the fan was turning when it should not be.

    Anyone have similar experience? I want a bit more input before I spend the $$ on the fan clutch.

    Thank you,
    Larry
    Amonster Motorsports
    1999 Suburban 7.4l

  2. #2
    Jr. Engineer
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    Default

    im assuming you have a machanical fan clutch and not an electric one. the machanical ones will turn when the engine is running reguardless of how hot the engine is. does it sounds like a jet engine all the time when you give it gas? thats the "typical" idications that the fan clutch is enguaged.

    also, get a scan tool and checked coolant temp from the pcm. that is a much more acurate reading. temp gauge on 2009 dmax reads "210" but the ecm says engine temps 188. just somethign to think about.
    "i dont think you got the picture. i got a beautiful picture. this baby happens to have an extra turn of speed, which is the only thing i care about. you dont understnad what happens do you? they make cars. they make 'em exactly the same way. one or two of 'em turn out to be something special. nobody knows why. i know why. i may be kiddin' myself, but i think i can make somethin' out of that sad little bucket of bolts." ~ Tennessee Steinmetz

  3. #3

    Default

    Quote Originally Posted by L5wolvesf View Post
    Hi all,

    In talking to a mechanic (pro) I know we noticed the air behind the fan was cold, really cold. Then we noticed the fan was turning when it should not be.


    Thank you,
    Larry
    The air temperature from the air being pulled by the fan from the radiator will really just depend on the coolant temperature inside the radiator and the A/C condenser coil when A/C is ON. With the engine at operating temp and the air being pulled is cold, then you don't have any heat exchange at all from the radiator. But it contradicts with your engine temp running too cold. I would think if there is no coolant flow to the radiator, it will overheat but it did not.
    It is strange.

    The thermostat should control the coolant flow to the radiator unless it has a by-pass.
    2011 Chevy Silverado LT 4WD 30k miles
    2001 Suburban 2WD, 5.3, V8 185k miles
    1993 964
    1996 318TI

  4. #4

    Default

    Quote Originally Posted by a.graham52 View Post
    im assuming you have a machanical fan clutch and not an electric one. the machanical ones will turn when the engine is running reguardless of how hot the engine is. does it sounds like a jet engine all the time when you give it gas? thats the "typical" idications that the fan clutch is enguaged.

    also, get a scan tool and checked coolant temp from the pcm. that is a much more acurate reading. temp gauge on 2009 dmax reads "210" but the ecm says engine temps 188. just somethign to think about.
    The fan clutch should disengage when the engine is running at higher rpms, correct? Yes it does sound loud when I run the truck up fast.

    Mechanic mentioned ‘burb gauge clusters tend to be problematic, he says some people have had to send them to GM for refurbs.

    - - - Updated - - -

    Quote Originally Posted by bazar01 View Post
    The air temperature from the air being pulled by the fan from the radiator will really just depend on the coolant temperature inside the radiator and the A/C condenser coil when A/C is ON. With the engine at operating temp and the air being pulled is cold, then you don't have any heat exchange at all from the radiator. But it contradicts with your engine temp running too cold. I would think if there is no coolant flow to the radiator, it will overheat but it did not.
    It is strange.

    The thermostat should control the coolant flow to the radiator unless it has a by-pass.
    Once the rad was refilled and the engine was running, only for a minute or so, the coolant started to flow. It was hot to the touch, but a pyrometer reading at several points showed the temp way below the t’stat rating (195).

    No bypass far as I know.

  5. #5
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    Quote Originally Posted by L5wolvesf View Post
    The fan clutch should disengage when the engine is running at higher rpms, correct? Yes it does sound loud when I run the truck up fast.
    the fan clutch never actualy "disengages". it will never stop spinning. when the clutch enguages it will bring the fan up to engine speed which is when you hear the jet engine noise. if that thing is always engauged it will cuase it to over cool. clutches are ususaly pretty cheap so you could just repalce it if you concerned anyways.

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