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rising temp + noise from front = fan clutch?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by jms, Apr 22, 2002.

  1. jms

    jms 1/2 ton status Author

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    350 w/ recent vortec head swap, Q-jet, TES headers, checked timing, plugs look o.k., and I'm on my fourth thermostat since the head swap /forums/images/icons/smile.gif:

    Lately (within the last week or so), I've noticed an increase in engine temp every time I step on it - even if I'm on it very lightly. Also, at idle w/ A/C on, temp goes up (which it has never done before) and then is a bit erratic; outside temp was like 50; A/C on max cool, so no on/off cycling. It has also developed a deep noise that appears to come from the front, possibly the fan, but can't be more specific. As far as I can tell, it doesn't ping (not with 4 deg and not with 8 deg timing). Fan can be turned by hand with some resistance; haven't had a reason to assume that the radiator is plugged. I'm running a new Steward water pump.

    Fan clutch going bad? Other ideas? Thanks for the advice, michael
     
  2. weisel

    weisel 1/2 ton status

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    Are you checking the fan clutch by turning it when the engine is at its hottest?
     
  3. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I just got my vortec motor going and it was doing the same thing. I took the radiator to be cleaned and changed the fan clutch. It was doing 235 with the heat off and 210 with it on. It now runs around 190-95 range.
     
  4. jms

    jms 1/2 ton status Author

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    Nope - engine cold. So it should have resistance. If it really is the clutch, that would make it two in ~10k miles...

    BTW, I'm now thinking electric fans, maybe two Perma-cool 14 inch with (supposedly) 2950 cfm and only 10 AMP draw each, and keep the old fan in the boonie box. Not sure what to do about a shroud.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Actually shouldn't need a shroud, it would just block the flow through effectiveness of the huge radiator opening on the truck. IMO run the largest electric fans that will fit, with the least amount of shrouding possible.
     
  6. MudbogAD

    MudbogAD 1/2 ton status

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    When my fan clutch went out it didn't make any noise but it does look as if that is the problem with yours.
     
  7. Blue Meanie

    Blue Meanie Registered Member

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    have the radiator flushed or change it, check your hoses and change to a 160 degree thermostat. also pull the belt off the water pump and see if the bearings are bad by trying to pull it up and down, side to side. if it moves, change it out.
     
  8. jms

    jms 1/2 ton status Author

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    I always thought that the function of the shroud was to ensure that the fan pulls air from the front - i.e. through the radiator - and not from the side. So, if I understand you correctly, all that is needed is essentially some sort of ring around the fan perimeter to channel the airflow, and mount as close to the radiator surface as possible?

    BTW, I like your sig line, although it seems to me that throwing money and troubleshooting are not necessarily mutually exclusive...
     
  9. jms

    jms 1/2 ton status Author

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    Radiator flush is on my to-do list. Hoses are new. Pump is brand new, everything is tight, and the pump makes more than enough pressure - one of my four t-stats was sticky, resulting in a leak at the gasket. I've been sticking to the 190-195 t-stats acc. to factory specs, but I'll keep your advice with a lower tempt t-stat in mind if these temp fluctuations aren't going away after dealing with the fan clutch. I had thought about this but was concerned a lower temp t-stat would lower engine operating temp too much.
     
  10. Chris_T

    Chris_T 1/2 ton status

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    Am I worng, but that seems backward to my thinking .. the fan clutch should be free when the engine is cold as to not rob power until the fan is needed, then as the engine temp warms up the clutch engages to start pulling air at high temp? IMO a fan shroud with the fan blades protruding out the back is more effective than running without onw as it does pull more air through the radiator, rather than moving it from the side of the engine.

    If I'm mistaken onthe fan clutch can someone correct me please. I was thinking of adding a clutch to the fan on my '72 before my cross-border trek.

    C
     
  11. jms

    jms 1/2 ton status Author

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    Seems like you're right, and I probably got it wrong. Although at this point I'm getting too fed up with the fan clutch on my engine, so I will probably select option number one from Dorian's list /forums/images/icons/cool.gif and call Summit tonite...
     
  12. 76chevy

    76chevy 1/2 ton status

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    I just ordered the same 14 inch fan from summit. I only ordered one for now and I will probably order the other one when I get my AC up and running.

    I'm running without a fan now and I don't start to heat up unless I sit still for a long time. Hopefully the one fan will work for now. Eventually it will be a dual fan with an on off switch, adjustable thermostat and relay for AC or extra hot conditions.

    I'm amazed at the power I've gained since getting rid of the fan. I should have gone electric along time ago. Way better gas milage too and on top of that my truck sounds like a truck and not a big fan.

    Good luck on the conversion.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    160 thermostat IMO isn't a good idea. The benefits are almost nil, and the negatives are worse economy, more internal condensation, and less metal expansion which is figured into clearances when the engine is built.

    Besides, changing the thermostat may help with the fluctuation if the thermostat is bad, but if the thermostat isn't what is causing the major fluctuation, the problem won't be anything but "masked" or hidden by a lower temp thermostat, yet it will still exist.
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, it is, but also to force the air straight back and through the blades....however, with the fan right against the radiator (electric) and much smaller/narrower blades, and with most electric fans having a small 'built in" shroud around the outer edges, a big shroud is unnecessary...you may as well not block flow through the radiator if you don't need too. (which is what you said)

    Even the factory truck shroud doesn't directly cover the radiator, but it does act as a funnel. A fan itself will act as a restriction, just from being there, but at cruise, the fans shouldn't even be needed.

    The air dam and radiator support in the trucks are the primary methods that force air through the radiator at cruise. As someone else mentioned, running without fans should only be a problem at idle or very low speeds.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    No, thats why a properly operating fan "roars" when the vehicle is started (cold) then "shuts off" if you let it idle.

    Stock fan clutch is both viscous and mechanical. Viscous is the silicon that leaks out sometimes, and the bimetallic coil on the front is the mechanical part...the viscous lets it slip when it's "off", the bi-metallic "locks and unlocks" the clutch at the factory "preset" temp.
     
  16. bklynlifted

    bklynlifted 1/2 ton status

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    what is you opinion on flex fans?
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    Worthless. Might as well put cardboard in front of your radiator when you are going to go on the highway, and while your at it, why not tax your waterpump bearings too? /forums/images/icons/smile.gif

    Seriously. They theoretically rob HP (always turning whether needed or not) and them flattening out at high RPM does nothing but create a huge restriction behind the radiator, preventing efficient flow through cooling.

    Used to have alink to a picture of a flex fan blade sticking through the hood of a C/K truck, but the link went dead. That pretty much sums them up for me. /forums/images/icons/smile.gif
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    Oh yeah, thanks for the sig line compliment. I just figure its cheaper to go buy a multimeter or scan tool than it is to replace the battery, alternator, and battery cables, and all the engine sensors.
     
  19. jms

    jms 1/2 ton status Author

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    Isn't the operating temp of a carbed engine somewhere at 180 to 190 degrees?

    So, I suppose a fan ought to come on some 5 degrees before the t-stat opens?

    By the way, thanks for all your input; it is greatly appreciated.
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    Thats GM's pre-determined engine temp. If they wanted, they could have made that higher or lower, dependent on how they wanted the system to work.

    GM's lit says something like a 10-15 degree variation in the thermostat "fully open" temp is "acceptable" so I'd think the fan temp would be much higher. In my experience (with the really overbored motor) the fan came on at about 210 degrees. So thats theoretically 15 degrees AFTER the t-stat has started opening, or is open. It IS very effective, it brings the temp down fairly quickly when it needs to.
     

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