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Thermal or non-thermal?

U

ugly_blazer

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I think that I need a new fan clutch on my K20. It never runs hot unless I am running in the mud, which is close to full throttle. Otherwise, both idleing(sp) and normal driving are fine. With the engine off I can spin the fan and it will go around several times before stopping, hardly any resistance.

There are two different fan clutches offered for my truck, thermal and non-thermal. Which would be best for me? I do mostly street driving, occasionally pull a trailer and play in the mud.
 
On many of my trucks I have thrown the fan clutch in the trash, and replaced it with a spacer instead. It may cost you a small amount of gas milege, but spacers do not throw the fan into the radiator and destroy it when they go bad like fan clutches do.
 
I might be old fashion, but I say toss the fan clutch, and get a 16" or 17" Aluminum flex fan and a 3" spacer. It will help your engine to run a little cooler, but at the cost of a little fuel milege.
 
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I might be old fashion, but I say toss the fan clutch, and get a 16" or 17" Aluminum flex fan and a 3" spacer. It will help your engine to run a little cooler, but at the cost of a little fuel milege.

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Once you see a flex fan go through the bottom of a hood you'll go back to a regular fan. /forums/images/graemlins/eek.gif
 
I have never had a flex fan come apart on me yet (I have had many), but I am not saying it will not happen. anything has the posability of coming apart; even factory iron fans, which I have seen come apart. I have seen a couple of factory steel fans come apart on older vehicles, which had a 10 year old factory steel fan on them.

Most of the flex fans you can buy in any auto parts store will work fine on a Daily Driver (as long as you are not turning 5000 to 7000 RPM regulary), but are not meant for racing applications.
 
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It will help your engine to run a little cooler, but at the cost of a little fuel milege.

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This has been hashed over millions of times already, but to present the converse side of this argument...a flex fan is tied directly to engine RPM at all times.

A clutch fan is "removed" from the engine when not needed. Flex fans cost power when they are not needed (high vehicle speeds) and can't cool any better than factory (working correctly) at idle, since locked up the stock fan is the same as a flex fan.

Flattening blades is great in concept, but all that does is provide a flat surface to block airflow through the radiator and engine compartment.

One of the 4 wheel magazines did a cooling test, IIRC, flex fan did nothing to help. (the article is on my site, which I think is still in my sig, under "cooling" IIRC)

Again, not an argument, just another side.
 
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It never runs hot unless I am running in the mud,

[/ QUOTE ] Maybe this is your problem. If the mud clogs the fins on the radiator it's going to overheat. Changing fan types wouldn't help if that's happening.
 
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One of the 4 wheel magazines did a cooling test, IIRC, flex fan did nothing to help. (the article is on my site, which I think is still in my sig, under "cooling" IIRC)

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I have read several articles in Car Craft and Hot Rod magazines that say just the opposite, that flex fans (without a clutch fan) are much more effective (but not efficient) in cooling than a factory fan, but as you said this issue has been hashed out many times in many different magazine articles; both trying to support their own side of the issue. One of the main reasons I go for the flex fan without fan clutch setup is for dependability through simplicity.
 
TARussell turned me on to a sweet heavy duty fan clutch; application = 83 K30 454, 4spd, w/4.56 gears. I have these for both my crew cab and K5, this combined with a seven blade fan with eliminate most cooling issues (assuming the radiator is ok).
 
With all the different automotive products and parts to choose from there are a lot of different ways to build a vehicle, but as long as your vehicle looks and performs the way you want it to then more power to you.
 
If anyone wants to read it, it's here:

cooling test

Also interesting to note that their discovery about running no thermostat matched mine, the coolant temps did go lower, at least in certain circumstances. Straight water was very impressive though, if I could run without antifreeze, I would.

Very good point you make though, cooling is one of those areas that performance ALWAYS seems to be different between different setups, as there are so many variables. What works for you works for you. May take some testing to find the best setup, just stinks spending money to find it. /forums/images/graemlins/smile.gif
 
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With the engine off I can spin the fan and it will go around several times before stopping, hardly any resistance.


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Your fan clutch is wasted if you can make it spin any, should stop almost as soon as you let go. I would say go with the heavy duty thermal. Also make sure your antifreeze/water mixture is good.
 
The antifreeze/water mixture is ok, I add antifreeze after every mud hole. I just wasn't sure which clutch I needed. To complicate things, I don't have a fan shroud on either. If I can take the body lift off and not hit my t-case x-member (divorced 205) I will so it will be easier to run a fan shroud. It would be a good reason for another 2"s of suspension lift then too /forums/images/graemlins/peace.gif.
 
The reason I recommended the heavy duty thermal is that when it engages, the fan will spin at 90-95% of the water pump RPM. A standard duty fan clutch only engages about 70%.

This is obviously done intentionally, no reason to drag the power down more than necessary, but for our application, the heavy duty works just nicely.
 
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