I've made it through most hot summers with my Blazer running just under 210 degrees with the AC on in stop/go traffic. Never had an overheating problem. I would usually hear the clutch fan spin-up much louder as the temperature guage got close to 200 degrees. I used this as a base line to know that the clutch fan is working. This summer is different because I have not been hearing the roar from the fan when accelerating from a traffic light while the coolant temp is on the dot at 210 degrees. Driving in this near 100 degree Florida heat, my Blazer runs about 200 degrees with the AC on at highway speed. Idling in traffic shoots it past 210 degrees easy. I'm suspecting a bad clutch, but how do I know if my clutch really is bad? Any reasonable tests that I can do?

I feel a resistance when it's cold when I try to spin the fan by hand. Even after driving I feel the same level of resistance. It free-spins but with some resistance. I did a test where I'd drive around with the AC on, get it close to 200 degrees where I'd expect the clutch to be engaged from past experience, and then shut the engine off while observing the fan speed. What I observed is the fan free-spinning as the engine turns off. This was pretty close to 210 degrees.

Well, today, I said "&@#$ it I need AC" and let the temp get as hot as the first-to-second tick on the temp guage after 210 degrees (so about 215-220). While slowing down for stop signs in my neighborhood and accelerating again, I heard the roar from the fan kick in at nearly 220 degrees. Once I was at home in my parking spot, I popped open the hood (while the AC was running) to observe what the fan would do when I cut the engine. And the fan did stop completely (not free spinning) once the engine stopped. I then tried to move the fan by hand and felt the same free-spin resistance as before. So the clutch is engaging, just at way higher temperature than it did last summer.

Are these things adjustable, or is this a definite sign if a failing clutch? Everything else in the cooling system is new.

 

Is it possible there is an issue with your cooling system? Is your radiator and/or condenser clogged with debris, reducing their cooling abilies?

 

This is definitely something to check. The fan clutch only "knows" the engine is hot by sensing the hot air flowing through the radiator. If air isn't flowing through the radiator, its sensing ability will be reduced.

If the radiator and condenser are clean, then it sounds like a bad fan clutch. If you buy a new one, be advised that the "heavy duty" ones are ridiculously loud. It's best, IMO, to go with the "normal duty" AC-Delco unit.

 

I did just rebuild the intake manifold with new gaskets and such this past spring because I discovered I was loosing coolant and the reservoir tank was collecting debris. The reservoir tank is still collecting debris (probably residual left over from the worn intake gaskets now that the thermostat should be opening fully in this hot weather), so I will attempt another flush and go from there.

Last October I did install an after-market radiator I found on Amazon for dirt cheap. Same design as the OEM rad. I'm starting to wonder if this could be affecting the clutch fan.

 

DERP

I just realize what both of you meant by debris in the condenser/raditor: bugs and such.
Yep, I will pull the front grill off at some point and run the garden hose through the fins.

Thanks, ya'll.

 

Keep us posted.

And it is nice to try simple solutions first, even if they are less likely to be the culprit.

I was thinking about how a fan clutch could fail and it occurred to me that typically they have a coiled bi-metallic strip that changes shape and activates the clutch mechanism. I cannot see how the temperature at which this would activate would change. However, if there was a loss of the fluid inside the clutch or the mechanism that releases it was damaged, then it would not work as well.

 

Here is what the shop manual has to say about it:






George

 

Seems to be better now. Condenser wasn't really dirty, but I hosed it anyway, I straightened the fins some, and I drained/refilled the radiator/reservoir. Following George's troubleshoot guide, I still suspect a worn fan clutch which I will get to eventually. Temps seem under control for now.

 

Putting this thread to rest: the issue was indeed a bad clutch.

I wasn't sure at first because the replacement clutch I obtained from Autozone (Duralast brand) seemed to do some weird stuff. This Duralast clutch would be disengaged under cold temperatures and would stay disengaged while at operating temp if a certain engine speed was maintained. But then once engine speed stepped down (coming to a stop) while at operating temperature, the clutch would engage and then stay locked regardless of speed. I could still hear the loud fan well past 3,000 RPM and I dared not push it further than that. The clutch was engaging for some weird reason well before the truck reached peak operating temperature (with or without the condencer heating up). Something wasn't right here and it had me second guessing what the root cause is.

Turns out I just got a defective clutch from Autozone. I swapped it for another and now the fan noise is consistent with the temperature, speed, and if the truck was in a previous idle state. Good thing I chose this product for the "limited lifetime" warranty it has.

Something tells me that since it was this easy to obtain a bunk product (a well known name brand nonetheless, not some obscure Chinese product form Amazon), it might fail later down the road (or at least not last nearly as long as the previous 20yo OEM clutch did).
What have you guys bought that you'd recommend over Duralast?

Looking at the products on Rockauto, I'm wondering if I paid more for a product lesser than the OEM clutch. The aluminum fins on the forward facing side are different between the OEM and the Duralast. I don't know if the count or depth of these fins necessarily means "better", but I'm trying to figure out how to objectify the better product. What do you guys think? Should I stick with Duralast? The Duralast has so far been doing a well enough job keeping temps below 210 degrees in 95 degree weather.

 

Thanks for the update. These final posts are important so that we can learn from other's experiences.

As for the Duralast brand, I've avoided it but I really don't have a good reason why. I suspect that the Duralast label is slapped on products that are contracted by Autozone to be made by them. This means it is hard to tell who made it. Just today I came across on Rock Auto a Wix made filter that had been labeled as the Car Quest brand. I normally like Wix but I didn't know if they made a lower-grade filter for the Car Quest people or if it was they same as their regular filters with just a different name.

Those fins will be for heat dissipation but that is only one part of the equation. They would have to be balanced against what is happening in the clutch mechanism. So I don't know if you can use them as an indicator of quality.

Since you know what the fan clutch is supposed to do and what it sounds like when it is not working, I'd stick with the Duralast for now. If anything happens again with it, you'll be able to quickly diagnose the issue and get a new fan clutch.