Fan Clutch

I have an 2002 Dodge Dakota 8 cyl. 4.7 L engine, 272K. I’ve gone through 4 fan clutches in the last 2 years and could have gone through more. My mechanic can’t figure out why. I’ve replaced all hoses, radiator, water pump, T-stats, you name it. AC doesn’t work either. Probably just a leak. not sure yet.
Any ideas on why they keep dying on me.

How are they failing? Do they seize up? Do they not engage? Does the bearing fail? I would hope that after the second failure your mechanic replaced the fan blade assy as well.

Does the truck have an underlying overheating problem?

They don’t engage. With the engine hot you can grab the fan blade and hold it. Never had any underlying problem.

Are heavy duty fan clutches being installed?

To determine if a heavy duty fan clutch is required, lay the fan on flat surface and measure the height of one of the blades. If the blade height is 2.5" or more, a heavy duty fan clutch is required. If the height is under 2.5" a standard duty fan clutch will work.


Good ideas above. I’m assuming the fan is belt operated, with an electro-mechanical operated clutch to turn it on and off depending on how much engine cooling is required. If so …

Another thing to consider is that the pulley for the fan clutch might be out of alignment with the other pulleys. That can happen when a shop is monkeying around with the accessories, as there are various spacers used to get the belt alignment correct, and it is easy to get a spacer in the wrong spot. Ask your shop to check the alignment of all the pulleys on that same belt.

One more idea. Has the corresponding belt tensioner been replaced?

Look in front of the mechanical fan and see if it has an electric fan and if is functioning. All V8 Durangos had a hybrid fan system that year but I don’t remember if all V8 Dakotas did.

Anybody have any idea of exactly by what mechanism the fan clutch engages on this vehicle? I’m grasping here, but thinking that if the fan clutch relay has a high resistance contact and the engagement is magnetically based, perhaps the relay is dropping a large amount of voltage and leaving little for clutch engagement.

I know, I’m reaching and without any real knowledge… but hey, what the heck. Occasionally even we crazy people are right.


Thanks Tester.
Is this a fluid clutch, as I suspect, or are those vanes for heat dissipation?

If this is a fluid clutch, it may not be abnormal to be able to hold the blade while the shaft that drives the clutch is turning.

There seems to be something missing here. Exactly what are the operating symptoms that you’re struggling with? And under what specific conditions do they occur?


Unless there’s an overheating condition, the fan clutch is probably operating normally.


I also tend to think the diagnosis is not correct and especially so if the engine is not overheating.

A parts site shows both a fan clutch and electric radiator fan assembly for the 4.7 Dakota so I wonder if the electric fan is managing to keep things on an even keel without the fan clutch.

The Dakotas with the 4.7 came with a thermal fan clutch.

Going through that many clutches, I’d say that for some reason the fan itself is out of balance and prematurely wearing out the fan clutch. Bent blades…missing blades!!!

Unless my brain is only working on one cylinder, the fan is the only thing that could cause the clutches to wear out too soon. Or you’re buying your parts from some guy, out of his trunk at 38th and North and he also sells jewelry for your lady.


My GMC S-15 with the 2.8L V6 would do through a fan clutch every 30k miles. Luckily it was easy to replace.

Yosemite, do you know exactly through what mechanism the clutch engages?


Thanks for the link, tester, but it does not tell me anything I didn’t already know. As a matter of fact the bimettalic spring is clearly evident in the clutch photo. I’m trying to find out if the engagement mechanism is electromagnetic, mechanical, or through a viscous fluid. I’m guessing it’s a viscous fluid, which means that the ability to hold the blade still while the fan is engaged may not be abnormal.

I’m also still wondering what the actual symptoms are that the OP is trying to cure. Perhaps the fan is being blamed for symptoms that are being caused by something else.

A viscous coupling fan clutch doesn’t completely lock up.

One way to test a fan clutch is, when the radiator is cold the fan should spin a few times by hand. When the radiator is hot, the fan should barely spin one revolution by hand.

Also, when a fan clutch completely locks up, the fan will roar each time the engine is rev’d.


I’ve never had one apart @the same mountainbike, so internally I’m not sure.
I do know that the bi-metal spring is what actuates the clutch, and that it is the air temp passing across the spring that expands or contracts the spring to allow the fan blades to spin free or with the RPM of the water pump.

I presume that the center shaft where the spring is anchored must open some vanes internally that allow the viscous liquid to either flow, or be stagnant for lack of a better term.


I had one apart for my Toyota P/U. The bi-metal spring is attached to a screw shaft with a disk on the end. When the spring expands with heat, the disk is pushed closer to a smooth surface on the motor-driven shaft, giving the viscous fluid in between less area to work in and transferring more torque between them.

That’s my point: the OP stated that he was able to hold the fan blade while the fan was engaged, and described this as evidence that the fan clutch had failed, but the first thing that came to my mind was that this would not be a failure symptom of a viscous coupling. I don’t have access to technical documentation sufficient to find out if the fan clutch is a viscous coupling, so the question remains. I saw the bimetallic spring in the photo, so that answered that question definitively. Whatever the coupling mechanism is, it’s activated by a bimetallic spring.

My second question, that only the OP can answer, is exactly what the symptoms are that he’s trying to address. My gut suggests that perhaps the fan clutch is being blamed for the symptoms because it doesn’t engage solidly, but if it’s a viscous coupling that would be an erroneous assumption. We’ve had more than one OP suspecting his/her fan isn’t working because the engine overheats on the highway, for example, and that’s usually a simple misunderstanding of how the system works, and usually points to something else as a cause.

Until the OP posts back, I’m going to assume that it is a viscous clutch. If that’s true, than the very fact that the OP has to hold the blades to stop them from spinning suggests that the clutch is NOT bad. The very fact that he CAN hold them back suggests that the clutch is working properly. A viscous coupling would be designed to slip at higher speeds, those vanes being designed to increase surface area to more effectively dissipate the heat generated by the fluid turbulence. But without a symptom set, I can’t go any farther in helping fix the vehicle. I need the OP’s feedback.