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Stock Clutch fan

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Itali83, May 14, 2001.

  1. Itali83

    Itali83 1/2 ton status

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    I know that 90k5blaze has a similar post but this one it a little different. My 87 Jimmy has a fixed metal flex fan on it right now, for whatever reason the previous owner put it on there. I want to at least get the factory clutch so I will gain some H.P. back. My question is, should I also get the factory (I'm assuming plastic fan) or can I use my (I'm again assuming little bit bigger metal flex fan). I was thinking about electric fans but read all of the cons to it. Also I plow with my truck so in the winter time it works a little at low rpm's. I only do my yard so it is no big deal but still enough work. The factory clutch fans, does the fan acually spin faster than the engines rpm's at low rpm's and then cut out at high rpm's?? I just want to know if I can go half way and just buy the clutch or go all the way and get both clutch and stock fan. Thanks.
    Ben 87 Jimmy
    <A target="_blank" HREF=http://www.bens87toy.coloradok5.com>http://www.bens87toy.coloradok5.com</A>
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Actually most stock fans were steel, and clutched. (never seen a stock plastic fan that vintage) SOME used just a plain metal fan with no clutch, but that was relatively "rare". Go to the wrecking yard, or find one in the classifieds, inspect the blades for dents or bending, then buy the clutch for it from an auto parts store, or, if you are cheap and want to risk it (since they go bad eventually) buy a clutch out of a wrecking yard. Be advised, there are two sizes of clutches, cars typically got small ones, except for example wagons with a tow package. Truck clutches should all be large.

    As well, aftermarket clutches come in two types...the cheap one, which is NOT thermally controlled, and the more expensive type, which you want, that is thermally controlled. Easy to tell teh diff, the thermal one has a spring on the hub that faces the front of the vehicle.

    Stock fan spins no faster than the engine, however, when the engine gets hot, the thermal fan "locks" the blades, so they are FORCED to spin at engine RPM. I guess that s one advantage of an electric fan I didn't think about, they spin the same speed no matter the engine RPM. All thats good for though is cooling at idle, such as stop and go traffic.

    As to the "cutting out" the thermal control STILL overrides RPM, so if they vehicle is going 60, but over say 200 degrees, the fan should still be on, attempting to work. But once the temp gets to about 195 or so, the fan will "shut off" and unlock, so it will draw very little power from the motor.

    Check your "flex fan" to see if it has GM numbers on it (usually they marked every blade with a casting/stamping number) If it has numbers, and no other manufacturers name on it, then it is likely GM, and you may be able to use the blades, as they are seperate of the clutch unit. I would recommend a 5 or 7 blade GM fan. There are millions of them out there, you should have NO problem finding one.

    Dorian
    My tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
    No anti-theft measures on your truck? No pity when its stolen
     
  3. Itali83

    Itali83 1/2 ton status

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    Thanks very much for the ton of info. very helpful. So you would definitly change over to the clutch type fan?? The fan on it now I know has 6 blades. I haven't looked for GM numbers yet but you said they were either 5 or 7 blade. So mine probally isn't factory. I also heard that at high rpm's Like cruising on the high way, the flex fan flattens out and acually hurts the cooling, it makes a wall so the air won't flow through the rad. as well. If this is true, I'm definitly gonna at least get the factory thermal clutch. Thanks again!
    Ben 87 Jimmy
    <A target="_blank" HREF=http://www.bens87toy.coloradok5.com>http://www.bens87toy.coloradok5.com</A>
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    I wouldn't bet on 6 not being a stock fan, I KNOW for a fact there were 5 and 7 blade fans (3 also!!) but that doesn't mean there weren't six blade fans. I think the stamped in number on the blades would be an indication if it was gm or not more than anything else, or maybe a comparison to a GM one in a 'yard or something.

    Dorian
    My tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
    No anti-theft measures on your truck? No pity when its stolen
     
  5. Gopherkiller

    Gopherkiller 1/2 ton status

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    Hi guys, I would stay with the "stock fan." Alot of guys try and fix a cooling problem by blaming on the fan. What I'm trying to say, is don't be surprised if your outfit runs alittle hot, after you put it back stock. Hope that I made sence. GOPHERKILLER
     
  6. Itali83

    Itali83 1/2 ton status

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    Thanks guys.
    Ben 87 Jimmy
     

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