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The mkiv Supra Owners Club

Viscous fan operation


ManwithSupra

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Wondered if someone could enlighten me on the operation of the viscous fan.

I replaced my viscous coupling yesterday as my other one kept locking up when the engine got hot.

 

Took the car out again today and gave it the beans, however after parking up I am getting the rushing sound of a fully engaged viscous coupling as before.

 

Now I am starting to think this maybe normal operation. But could someone enlighten me on the operation? When the car gets hot is it supposed to run the same speed as the engine? or have I just gotten unlucky with a 2nd hand one.

 

Don't want to really buy a new coupling off Toyota and find the ones I have were fine anyway.

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  • 1 year later...

Just going through a check on my car with all the cooling components I thought I would ask here about my fan. Should the fan be stiff to spin by hand when the engine is turned off but still hot (90 degrees)? I'm not sure if I'm getting correct lock up when the engine is hot as I can still spin it freely when the engine is pretty hot.

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There should be some resistance, yes, but not so you have to use much effort. You shouldn't just be able to flick it and spin it though. Usually if the viscous fails they either lock up (seize) or leak silicone fluid. Modern ones are pretty reliable! You do NEED that shroud, will make at least a 70% increase in air throughput. Can't stress that enough.... Without a shroud the fan will draw air from the easiest path, which is NOT through the rad core.

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There should be some resistance, yes, but not so you have to use much effort. You shouldn't just be able to flick it and spin it though. Usually if the viscous fails they either lock up (seize) or leak silicone fluid. Modern ones are pretty reliable! You do NEED that shroud, will make at least a 70% increase in air throughput. Can't stress that enough.... Without a shroud the fan will draw air from the easiest path, which is NOT through the rad core.

 

Well theres no fluid leaking and it's not seized but it spins for a couple of seconds if I spin it by hand so it should be ok. Ive got a shroud on its way to me soon so this should solve everything. Thanks for the help Chris.

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It certainly should NOT spin for a couple of seconds, it should stop almost immediately if you flick it round from stationary. Looks like it needs a new viscous coupling.

 

Ok I will check again just to make sure then order another one if it seems to spin more than it should.

 

Also the new fan shroud comes with 2 small electric fans but I only have a wire for one fan on my car, can I wire these both to the same wire or a manual switch inside the car?

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I would need to study the schematic to see how Toyota wired these. I know at least one comes on with the air con, and probably also if the temp switch in the bottom rad tank switches. I haven't time to dig them out and look at the moment, sorry. If you can find them and post the relevant section I'll try and have a look for you if you can't read it yourself.

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I would need to study the schematic to see how Toyota wired these. I know at least one comes on with the air con, and probably also if the temp switch in the bottom rad tank switches. I haven't time to dig them out and look at the moment, sorry. If you can find them and post the relevant section I'll try and have a look for you if you can't read it yourself.

 

No worries I have the manuals to hand now ill have a look.

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