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I need you guys to check your cooling fans for me!!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Can Can, May 19, 2001.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I've been trying to solve a cooling issue for the last week. I replaced my thermostat- nothing changed. After talking with a lot of guys, I think I may have narrowed my problem down to a faulty fan clutch. If I turn off the truck after driving it for a while and pop the hood and spin the fan, there is almost no resistance from the clutch.

    I'm curious what your guys fans feel like after about 10 minutes of driving. If any of you are going out today, I'd REALLY appreciate it if you could check how hard it is to turn your fan after a drive. Apparently it shouldn't be that easy to spin by hand when the motor is hot.............

    Thanks in advance, brothers(and sisters)!!!!!



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  2. shane

    shane 1/2 ton status

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    When your motor is cold it should allow the fan to spin freely so the motor heats up quicker, once the engine is warm though you shouldn't be able to spin the fan by hand as it should be "locked". If in doubt, take it out.

    Shane


    Just keepin it Canadian[​IMG]
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    The resistance in a factory fan clutch depends on the temp and is controlled by a bi-metallic coil (technical term: "the little spring thingy on the front"). It should basically spin with very little resistance (there should always be some resistance, it should not free-wheel) until the engine moves into the upper portion of the operating temperature range where it should be growing steadily tighter. If your engine and engine compartment are hot (what does your gauge say?) and it is not very stiff, time to get a new one. If the engine compartment is not hot enough, you still should not be able to spin it even close to a full revolution unless it is completely shot.

    Bad Dog

    85 K30 CUCV, 350 TBI, TH400, NP205, D60/C14, 4.56 Locked
    Soon: 4" lift, 40" tires, massive cutting, shorter wb and rear overhang.
     
  4. GRINCH

    GRINCH 1/2 ton status

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    Just took mine for a 20 min run. Temp was 180. Checked it before I left, spun fairly easy. When I got home it was a little tighter but not much. Mine is factory 11 yr old.

    The Few, The Proud, The K5 Blazer
     
  5. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    With the engine at around 190 I can spin the fan about a third of a revolution with a flick of my finger. When the motor is cold there is tons of resistance from the clutch.........

    My truck has been running about 15-20 degrees too warm for the last week- unfortunately it's been off and on so I can't really pinpiont the problem. The reason I want to be sure that the fan is shot is that the replacement is about $130 up here- I'd hate to spend that kind of cash if the fan isn't the problem!!!!



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  6. FWP

    FWP CRS

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    Allright, what kind of test equipment can you get hold of? Specifically, an IR temp gun, and a photo tach. If not, there's no way to tell for sure, by feel, IMHO. If you can get the meters, let me know, I'll explain further. HTH

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  7. ChevyCaGal

    ChevyCaGal 3/4 ton status

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    I didn't drive it today but I did start it...it warmed up so I checked for the heck of it to see what it did. With a cold engine I could spin it by hand. When it warmed up my fan wouldn't turn at all by hand....anyhow thought I would toss what I found in. Good luck solving this! [​IMG]

    "Suck Fumes Ford Boy"
    "I love my country, I fear my government"
    <A target="_blank" HREF=http://www.chevycagal.homestead.com/steph.html>http://www.chevycagal.homestead.com/steph.html</A>
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I have a lazer temp gun at work...............the other, heck, I don't evem know what a photo tach is!!!!!!!!!!!! I'm almost positive the clutch is bad- It's doing the opposite of everyone elses. Mine's hard to turn when cold, easy when hot..............

    Man, I hate it when something just KINDA breaks[​IMG]!!!!!!!!!!!!!!



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  9. backlash

    backlash 1/2 ton status

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    Makes sense that it turns easy when cold to allow the engine to warm up. Then turns more difficultly when hot ... but you already know that.

    Mine does that too ...

    I'm curious about the high tech info test.
     
  10. FWP

    FWP CRS

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    The way I test mine:

    (A photo tach emits and receives a light beam, and counts the relections, giving you RPM)

    Start engine cold, run at 2000 rpms. note fan speed using photo tach.

    As the engine warms up, the fan should slow down.

    Block the radiator with something, but leave a hole where the fan clutch is. The clutch needs to get very hot.

    As the engine temp keeps climbing, the fan speed should then increase (this is where the IR gun comes in- DON'T overheat the motor!) I dont trust factory gages- hehe.

    Remove the cardboard or whatever from the radiator, as the motor cools back down to normal temp, the fan rpm should go back down.

    Kinda weird how that works inside the clutch, but that's it.

    Did all that make sense?


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  11. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Thanks for the idea................I'm going to take the truck out for a while today and then spin by my work and take a temp reading of the thermostat housing with our lazer temp gauge(we use it to measure the temperature of our plastic pipe fusion irons).

    I'm a little les worried than I was a week ago. We went to visit some friends that were camping up in the mountains about 30 miles away. I kept a close eye on my temp gauge and the highest the gauge got to was about 205'. I'm starting to think my temp problems have something to do with the fact that I upgraded my aux. tranny cooler this year and blocked airflow through the rad a bit more than before. I'll keep you posted when I get the results.

    BTW, 205' isn't too hot for my motor, is it?



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  12. Itali83

    Itali83 1/2 ton status

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    By my factory guage, I run 210 to 220 all the time. But my shop says the truck is only running at 195ish. I don't know which is true. but I do know that factory guages are junk. Just tellin ya.
    Ben 87 Jimmy
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