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Fan clutch vs. Flex Fan

Discussion in 'Chevy Trucks' started by Jamaray, Sep 1, 2003.

  1. Jamaray

    Jamaray Junior Member
    Messages: 3

    Just bought my '85 Chevy K10 four months ago and started having cooling problems. I first checked all hoses by tightening and replacing as needed. Then, had the radiator flushed and reflused (very dirty) and replaced the original radiator cap. When all was said and done the cooling system was not leaking, however, whenever driving above 50-55mph the temp. gauge would rise well above 240 and spill out the overflow. Since, the weather here was over hitting 100 degrees F. daily, I refilled with a 60/40 antifreeze mix and replaced the fan clutch with a 6-blade fan.

    I haven't gone above 210 on even a hot 106 degree day traveling a 75mph. Which, is great except for the fact I have been told by many that a fan w/fan clutch would give me better power and fuel economy.

    My question what is the better method: fan clutch or flex fan?
  2. wyldman

    wyldman Member
    Messages: 3,265

    The fan clutch is a better setup if it's working as designed.If the clutch fails to kick in,or the fan doesn't have enough blades,it will perform poorly.

    Something doesn't jive with your problem.If your driving over 50 MPH and it overheats,it's NOT a fan problem.You could drive around all day at speed without a fan.
  3. BWhite

    BWhite Senior Member
    Messages: 496

    flex fans

    What I remember from a LONG time ago .....there was a big recall on a flex fan because the fan blades were flying off and causing havoc . I am sure it doesnt happen now but a clutch fan is a better idea
  4. Pelican

    Pelican 2000 Club Member
    Messages: 2,075

    Did you replace the thermostat when you serviced the cooling system? Seems kind of funny that the problem disappeared with the fan replacement. The whole idea of the fan clutch is to allow the fan to freewheel at highway speeds because the fan is usually not needed for cooling at that point.
  5. porkhead1

    porkhead1 Member
    Messages: 70

    If all is working well, at highway speed a clutch fan is just free-wheeling w/ the air flowing thru the radiator causing it to spin. So, if you're running hot at highway speed, you may want to replace your radiator. You never mentioned how hot you're running at lower speeds like city driving. You may want to replace your std. 195 thermostat with a 180. With a cooling system in good condition, you'll get plenty of heat for the cab of your K10.
    I remember reading somewhere that a mixture of 60/40 will raise your coolant temp. too. A 60/40 will lower your cooling system freezing point, but may not help your operating temp. Try a regular 50/50 mix. Also, did you check your belts...?? A leaking water pump may be dripping antifreeze on to the belt, causing it to slip....
    A good clutch fan set-up for a small-block Chevy was the 7-blade fan w/ clutch-drive from a 1970 1/2 Chevy 350 LT1.

    Just my $.02.......

    Good luck
  6. wyldman

    wyldman Member
    Messages: 3,265

    It is possible that maybe the clutch fan was the wrong one ? If it is from a newer truck,then it is a reverse rotation fan,and should spin the other way.It would try to push air through the rad,and not pull it.It would be fighting the incoming air at speed,causing low airflow across the rad,and overheating.You might want to check the blades,and see if they are opposite from the new fan you installed.
  7. 78K20

    78K20 Member
    from WV
    Messages: 49

    flex fan

    I have a flex fan on my 78 chevy . It was on there when I bought it. I haven't had any trouble with it yet. You can see where the other fan exploded and went throught the shroud. It then put a big crease/dent in the bottom webbing under the hood. Good thing someone wasn't looking under the hood. I think there was a big recall on the original fans?
  8. Jamaray

    Jamaray Junior Member
    Messages: 3

    Thanks for all the replies..:salute:

    I did not know that the fan clutch became freewheeling. My understanding was that at higher speeds it spun faster to help w/cooling..misconception on my part.

    At lower speeds with the 6-blade fan, my K10 rarely goes over 160 degrees and at higher speeds on hot days (95-100) has stayed just below the 210 mark on my temperature gauge. And I originally thought of changing the thermostat, but have not.

    The old fan clutch was a 3-blade fan and clutch. Would the change to a 6-blade fan have created better cooling?

    The truck runs fine, just sounds like a jet engine taking off in first gear. :yow!:

    CARDOCTOR PlowSite.com Addict
    Messages: 1,304

    sounds like the radiator is starting to block

    my monte ss use to do the same thing
    had the rad shop flow check the rad it was restricting coolant flow

  10. Pelican

    Pelican 2000 Club Member
    Messages: 2,075

    Jamaray, your fan does not contribute to cooling at highway speeds if your system is working correctly. That's why the fan clutch improves fuel mileage, it reduces drag on the engine when it's free wheeling at travel speeds.

    The switch from a 3 bladed fan to 6 or the flex fan shouldn't have made any difference at highway speeds, there's supposed to be enough air flow to handle the cooling. This is why we think there's another problem. Perhaps the belt was loose and you tightened it to spec when replacing the fan. A slipping belt would prevent the water pump from working properly.

    Chris, I have a question about flex fans. I remember they flatten out at higher rpms to lower the drag on the engine, so wouldn't they cause overheating if you had an accessory to drive while parked like an inverter or generator?
  11. Joey D

    Joey D Senior Member
    Messages: 280

    Is the fan on all the time? It will block air flow at highway speeds if it does not free wheel.
  12. wyldman

    wyldman Member
    Messages: 3,265

    That is just a myth.If that were the case,then any fan would block airflow.A clutch fan is no different.The only purpose of the clutch fan is to save fuel and reduce power loss.
  13. wyldman

    wyldman Member
    Messages: 3,265

    That is just a myth.If that were the case,then any fan would block airflow.A clutch fan is no different.The only purpose of the clutch fan is to save fuel and reduce power loss.
  14. wyldman

    wyldman Member
    Messages: 3,265

    The amount of airflow at higher engine speeds,and fan speeds,even with the fan flattened out some still exceeds the amount of air required to acheive an acceptable temp drop across the radiator.I don't think it would be a major problem,as the fan don't actually flatten out completely.
  15. Joey D

    Joey D Senior Member
    Messages: 280

    Chris, I had a bad clutch on my 88 GM pick up. The fan was locked on all the time and when you hit the highway it would run hot, 210 or so. It would only do it once you got over 50mph.
  16. wyldman

    wyldman Member
    Messages: 3,265

    I doubt it was the fan or clutch.You could run a solid fan,or no fan at all at 50 MPH,and it shouldn't make a difference.
  17. Joey D

    Joey D Senior Member
    Messages: 280

    Chris, With the fan roaring away on the highway it would run hot. New clutch, no problem.
  18. bad dad

    bad dad Junior Member
    from canada
    Messages: 6

    you want the best is to go elec.fans look in your auto shops you will find it is the best . more hp and beter economy andytami@telus.net