Such a thing as a fan clutch thats too efficient?!

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May 1, 2019
NSW, Australia
So I have a bit of a funny one and have done some searching but nothing really putting my mind at ease. Is it possible that the viscous fan clutch/hub is working too well?! As in is running too often or pulling too much air (if there is such a thing?) Below is some context to my question:

2003 Aus spec UZJ100 5sp automatic, Radiator is brand new (koyorad), with new coolant. (was replaced when original 16 year old rad sprung a leak - not because of any apparent cooling issues)

Thermostat condition is unknown, however car warms up normally to 88°(190° for my US friends), then holds within normal ranges of 85°(186°) to 88°(190°), with normal driving. I have seen it briefly hit around 90°(194°) once when I was stuck in some traffic but thats as warm as ive seen it. So I believe it has an 88° thermostat that is working as it should.

The viscous fan hub condition appears good, testing it with warm engine immediately after shutdown the viscous hub is firm/fan does not freely spin. Cold start up fan locks up and spins with engine for about 10-15 seconds then slows down (which I understand is normal for cold start up while all the fluid circulates in the hub)

Now this is where the funny bit comes in. The car does not overheat, in fact what has me looking into it is it seems to run a bit too cool, and the fan seems to lock up with the engine all the time during normal operation, even when it is running below normal temps.

For example, I just arrived home from a trip up the mountain, inlet air temps were between 11°(52°) and 18°(65°) most of the trip and the temp sat around 86°(187°) most of the way, however on the way back down the hill I left it in 3rd and coasted all the way back down (about 10km windy road top to bottom). Now while observing the temps and fan operation, I noticed that the viscous fan seemed to be locked up with the engine revs the entire time, the inlet air temps were slowly rising as I got further down the hill, however the engine coolant temp was steadily dropping...
At the bottom of the hill, still in 3rd, viscous fan roaring away, inlet temps were just over 20°(68°) and engine coolant was sitting at 78°(172°)!

Went back into drive, back up to 100kph and temps went back to normal of about 86°.

Am I just freaking out about a super efficient cooling system?
Is it normal for the viscous fan to run that much? (or maybe constantly when in a lower gear, which would be odd I thought seeing they are purely temperature driven?)
I have noticed that more often than not when I slow right down and transmission drops back to first, when I start to accelerate again the viscous fan is often engaged, and when it is engaged there is a noticeable load on the engine - thats the thing out of all of this that has me wondering, as clearly I dont have overheating problems at this rate!
a bit more info - this is the spring on the fan hub. Obviously it's not brand new, is it possible for them to fail 'the wrong way' and engage too much
I think the clutch fan is affected by the speed/resistance of the air rather than the temperature. At highway speeds, the clutch will be spinning slower from the force of the air pushing against it. With no air pushing against it (at a stop), the fan should be spinning just fine.

I hope that made some kind of sense. It's late, I'm tired and I doubt I can coherently write my own name.
Have you checked that the fan clutch has the right CST (centistoke) oil in it. (viscosity). To make sure, I would suggest you take the Fan Clutch apart, and clean out what ever oil is in there. You will end up with two halves, one will be flat and the other like a clam shell. Pour new 10,000 CST fan oil in the the clam shell side, and reseal it.
I know that people do not usually think about fan clutches, but they are very important. There are a lot of Fan Clutch Oils around which are sold by cowboys (In CUBA they use VO5 shampoo, I'm not kidding) some are 3,000 and 4,000 CST which are not dense enough. Unfortunately I live in New Zealand and produce 10,000 CST Fan Oil, which we sell heaps of. Its not available in OZ unless REPCO decide to sell it in OZ as well as NZ. Toyota have 10,000 CST Fan clutch oil, but it costs an 'arm and a leg'.
Hope this helps,

It looks like this thread was brought back from the dead, but for future searchers…

The fan clutch fails to always on. I just had this when the seal failed. Sounds like the op had a failing fan clutch.
It looks like this thread was brought back from the dead, but for future searchers…

The fan clutch fails to always on. I just had this when the seal failed. Sounds like the op had a failing fan clutch.

X2 just changed a fan clutch for a lady, it was always on and the shop she normally went to couldn't figure out what the roaring noise was on acceleration.
Always check the fan bracket when doing a fan clutch.
the fan bracket had no movement but the serpentine belt tensioner pulley has play in it. I need to change that.

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