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Fan clutch


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Wise ones, I need you wisdom please!
My original fan clutch was shot, so I bought another. That one doesn’t seem to ever “turn on” and I can stop the fan blades with my fingers even with the gauge 3/4 across! I can make it work if I give it a couple of very brief blasts with the blow torch so the mechanism inside clearly moves.
I figured it must be just adjusted too high and ordered another. I just received an Aisin one from Rockauto, currently being tested as I type :p
At 85c it still wasn’t feeling any stiffer and I can’t imagine it getting much hotter than that when in the car.
So what temp is it supposed to work at? Nothing I can see in the FSM other than how it’s supposed to operate not at what temps.
One last thought, does it have to be spinning at speed to work or should I be able to turn it by hand and feel it become difficult to turn?

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You are too kind Mr Site! That is good advice sir I should be less fool hardy!!!!

I was playing hot potato with the fan clutch at 90c while holding it in a dishcloth. But I still couldn’t get it to go hard, so I’m wondering if it needs to be rotating at speed for it to engage!?

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I can crank mine and run it up to 2,000 RPM and within 30 maybe 60 seconds the fan comes to life. Sounds like an airplane under the hood. That's in a 60 F garage. I get it cranked and then flood the valve train with oil for that first minute, 1,500 to 2,000. The choke runs it to about 1,500 anyway so I add a little pedal. LOL (I have neighbors)

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“I have neighbours” ... Brilliant! :D

I bought 2x very good quality 10” fans from a UK club member for £20 and connected one up to an old 12v battery at the back of the garage today - wow!!! At full throttle, it does sound like a 747 but shifts more air than the rubbish Aeroline 16” one I just returned to eBay!

So both of those at half speed are going to cure my ills with fan clutches and be relatively quiet in operation.

In fact, I have a dual MOSFET circuit I built to drive as a purely analogue and constantly variable speed fan set up which will reverse direction for 5 mins when ignition is off and the car is hot to reduce heat soak. Having said that the FETs get awfully hot and I’m going to experiment with either having the heat sink in the air flow or the PWM driver also sitting on the bench. PWM is a way more elegant control mechanism, but if you get the frequency wrong you can fry motors easily with back EMF issues. I also have a solution in mind for that ;) so watch this space if I ever get enough time to do it all this summer!!

This is what it looked like here yesterday @ 08:00


And the same place 8 hours later!!


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In the first post you talk about a mechanical fan. I'd stick to that it's simple and reliable..

You could like i did open up the old clutch mechanism. These old clutches dry up and need just a little bit fluid to work again.. i personally opened a 280zx fanclutch  (Clean it thoroughly first.) and used a bit of wd40 to get the mechanism working and closed it up.. you don't need a lot of fluid.. (Nice to see how the fluid locks the mechanism as it gets hot.)

When installed it should go no further then 1/2 or 3/4 round when you give it a good try to make it go round. The clutch engages more and more as temperatures rise .. normally on room temperature the clutch is disengaged but it still brakes a lot..   When hot you could stop it but you'll need a piece of wood and you might brake the fan blades that tough it will get. (So test it when off and hot it will turn very difficult.)

When your gauge stays under 3/4 hot then thats oké... i think..? At normal driving the meter should be half way though..

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Thanks dude. I also like mech fans! Unless you lose the fan belt, they never fail completely and look period.

I did start by trying to restore the original clutch but the mechanism has rusted solid.

The next clutch is factory sealed without bolts to open - I would have to drill it out but even if I tapped it and put bolt in, the mechanism doesn’t want to work until well over 100c - by which time it’s way too late.

The third (Aisin brand as yet unfitted) is super sealed and even harder to drill out if I wanted to! The oven test last night didn’t yield a positive result so next I will test it on the car maybe a little more violence in spin will make it engage.

I will absolutely have the electric fans regardless, as supplementary fans and an insurance policy for that very hot day.

Also reversing them for a few mins after shutting down will reduce the heat soak on all the rubber / wiring under the bonnet on that hot day. I have temp sensors ready to install and experiment with around the engine bay, so again watch this space. In the meanwhile, this is a great read ...



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I would be really interested in your fan controls and how to make one!

Let me get it working safely first and I’d gladly share it. (I’ve melted one FET already with too small a heat sink - good job I have 12 of them :p ).

Edit: I discovered today that my Q5 uses one of these right behind the fan! I may just get one as it’s beautifully packaged! I strongly suspect they have solid state electronics in there given the heat sink arrangement!


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