Viscous Fan Coupling - How To Test ??

Submitted: Monday, Jan 01, 2007 at 21:54
ThreadID: 40778 Views:32256 Replies:9 FollowUps:2
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Hi guys & Happy New Year to you all,
I've been nursing the cooling system along on the 4.5 auto 80 yota, but l want to iron out the symptoms so l repair only as needed.

On v.high temp days, crawling along in traffic, the temp starts to climb towards the red. Other days and/or not crawling along, it remains rock solid at about half gauge level.
I know the header tank has a slight leak along the crimped joint. The apparently it's not repairable as the rad is old - New Rad = $$$$ great start to N.Yr.
But is the viscous fan drive faulty too??

A mate reckons that when the parts are new, you can grab the input and ouput shafts of the viscous unit and as they are turned against each other (a lot!) the 'coupling' between them stiffens up. Thus on an old part, if it doesn't stiffen or is solid/seized - it's no good.

It was also said that you should be able to stop the fan (at idle) with a folded bit of cardboard but as revs are increased, the fan will 'couple' and drive 100%. However a US website says if you can stop it at idle, its buggered anyhow. Confusing, contradictory advice!

As mine is in the car, l cant try the 1st idea. However the fan is driving and wont stop with a bit of cardboard - it's not seized either. What does that mean?

Another sympton mentioned to me is that a lazy viscous coupling will affect the a/c ability to cool the car. My old R12 system is now filled with R143a (plus new drier) and doesn't cool as well as it used to either, thus swaying me toward thinking that the viscous coupling may be lazy.

Any other ideas on how to test this would be appreciated.
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Reply By: MartyB - Monday, Jan 01, 2007 at 22:22

Monday, Jan 01, 2007 at 22:22
One thing to look for is a "runny nose" on the coupling. If there is signs that oil has leaked out of the front centre then it is probably stuffed.
Another way that is not recommended is. Drive until engine is at normal opertaing temp. Stop the engine. Hold onto the fan while someone starts the car, if you can stop the fan from turning the coupling is stuffed. If you are missing some fingers it is probably ok.
I have heard that cruiser couplings can be topped up with more oil, don't know if this is true.
from Marty.
AnswerID: 212793

Follow Up By: Member - Phillip S (WA) - Monday, Jan 01, 2007 at 23:54

Monday, Jan 01, 2007 at 23:54
Love the bit about the
FollowupID: 473000

Reply By: Big Woody - Tuesday, Jan 02, 2007 at 06:33

Tuesday, Jan 02, 2007 at 06:33
Hi BoB,

I diagnosed a faulty viscous fan hub on my 80 series by getting the motor up to the higher than normal temperature. At this point I knew that the hub should be locked to the motor to try and bring the temp back down.
With the bonnet up, motor running and my left hand on the ignition key, all I did was turn of the engine and watched the fan. It did not stop with the engine but continued to freely spin.
Picked up an aftermarket viscous hub for $110 and my cruiser has never gone above half again.

Good luck,

AnswerID: 212814

Reply By: Member - DOZER- Tuesday, Jan 02, 2007 at 07:52

Tuesday, Jan 02, 2007 at 07:52
To check fan
....start motor. listen to fan noise,note revs... note it quietens down after 30 seconds or so. Drive till normal op temp...cover the grill side of rad with cardboard from the old case you have in the recycling....turb up fast idle to 1000 rpm again (like it was when started cold) watch temp gauge...if fan working correctly, a little past half way, the fan will kick back in and you will hear it do so.

To check fan no2 (this is what a friend did)
Install electric fan up front from old time it gets hot, turn on fan, notice your nose now has ice forming on it....and engine temp has dropped back to normal.
Change viscous, and leave other there aswell for turbo boosted air conditioning.
AnswerID: 212819

Reply By: Chucky - Tuesday, Jan 02, 2007 at 10:13

Tuesday, Jan 02, 2007 at 10:13
You can refill the viscus fluid in the fan clutch.

Only takes about 30ml. You can buy tubes of the stuff from toyota for about $15 each. I replaced all the fluid when I did mine and it used just under 3 tubes.

A really good DIY tech sheet is available at

I just follwed this and it only took me a couple of hours and everything was good afterwards.

I had to replace my water pump and when I went to get my rad, stripped and cleaned was told it was stuffed, so I decieded to replace the thermostat at the same time. The bloody thing was still getting hot towing my camper. Was told to top up the fluid inthe hub and it has never even looked like getting hot since. Have since crossed the simpson towing a O/R camper and done all sorts of things since with out a problem.
AnswerID: 212830

Reply By: Member - SKI er (NSW) - Tuesday, Jan 02, 2007 at 12:29

Tuesday, Jan 02, 2007 at 12:29
Hi Beast,

We had a similar problem recently with a 93 Pathfinder. Same symptoms. Another post from Chucky talks about replacing the viscous gel in the hub. his suggestions.

we had the added problem that our Pathy had a factory sealed fan hub. Don't know much about your vehicle. My mecahnics solution was to strip off the fan and the hub and drill a hole into the hub as close to the centre as possible... he then threaded the hole ready to recieve a grub screw.... he bought the gel from Totoya and filled a hpredermic syringe with it . He fitted the syringe with a wide bore needle and forced the gel into the hub and sealed the hole.

No trouble at all since and the Pathy now runs at 1/4 up the scale up hills or just a whisker hotter with a van on the back. He charged for 30 minutes labour plus the gel at $15.

AnswerID: 212842

Reply By: Member - Shane D (QLD) - Tuesday, Jan 02, 2007 at 17:59

Tuesday, Jan 02, 2007 at 17:59
Find a 4.5 in a car yard(s) and start it ,you should here the fan running and then drop of ,what your looking for is how much noise it makes and how long for.This should give you some indication of where your fan is at.try some of the simple test's(turning by hand) and then compare.
AnswerID: 212883

Reply By: acdc - Tuesday, Jan 02, 2007 at 20:48

Tuesday, Jan 02, 2007 at 20:48
The correct way to test a coupling.
With the vehicle cold, first thing in the morning! you should not be able to free spin the fan more than half a turn, anymore it's stuffed.
AnswerID: 212916

Reply By: Member - John R (NSW) - Tuesday, Jan 02, 2007 at 20:59

Tuesday, Jan 02, 2007 at 20:59
Dunno where you got that from acdc. My car's less than 2 years old and I can turn my fluid coupled fan as much as I like, albeit with reasonable resistance. I can assure you it's not stuffed.

That's not a true test of whether a fan's b**gered or not. The other thing that hasn't been mentioned is that the coupling should only be close to lockup when the unit is heated to whatever temp the coupling is designed to cut in at. This may vary between engine designs.

AnswerID: 212920

Follow Up By: acdc - Tuesday, Jan 02, 2007 at 23:06

Tuesday, Jan 02, 2007 at 23:06
Sorry only been in the trade for 32 years.
Of course you can turn it that's not what i said! LOL!!
FollowupID: 473137

Reply By: Philbee - Wednesday, Jan 03, 2007 at 22:42

Wednesday, Jan 03, 2007 at 22:42
ok temp rising crawling along or stopped in traffic would indicate the viscous hub not operating correctly but if the radiator has a leak at the header to tank seal, you would have pressure loss and also result in higher than normal coolant temp. yeah is expensive to replace the radiator but is repairable, (top tank part number TOY9244PT, O'ring P/N OR744X69R and Grip Plate P/N: GP744X69
Dont stick things in the fan to try and stop it, its dangerous and could also damage fan blades, when hot and idling you should be able to feel it pumping hot air towards the engine ( it sucks cold air from the front). and yes is cheaper to rejuvenate it than replace, the silicon oil from Toyota ( Part Number 08816-10001) is available in 18ml tubes, you need around 3 tubes to do a cruiser, just becarefull with the o'ring it's not available and in most cases when you take it out it stretches and wont go back.
As for your A/C, R134A is around 20% less efficient than r12, if your cooling system is working correctly you may find it 1 or 2 degrees cooler, but mostly the difference is on start up, R12 cools almost immediate while R134A takes few minutes.


AnswerID: 213114

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