For the first time in 3 years since I have owned my 80series my temperature last weekend moved from the half way mark to into the red and boiled the coolant. Investigations have found my fan clucth to have been the cause... anything over 2,000rpm and the fan would stop spinning. After reading Franks write up on fan clutch's, I decided to pull mine out last weekend and when I opened the fan clutch around half a glass of mud water came out.

Now, Im not sure if I should spend the money and replace the fan clutch or install some thermo fans. Does any one here run thermo's and what are your thoughts?

Definately dont go to thermo,s they are for street cars only
Clean out the hub then go down to toyota and buy 2 tubes of silicon oil for the hub (about 20 bucks) then reistall and try that first. If that doesnt lock the hub up then bite the bullit and buy a new hub . No thermo will keep a 4wd cool on a hot day when your engine is reving and your in soft sand doing 2kmh.
You can check if the hubs working by getting the motor warmed up so the clutch locks up then put a welding glove on hold the fan blade , you will feel if it has resistance ( just make sure you grab the fan side going down!. I had to go through this after installing a 6.5chev turbo that was a kettle.

Funny I'm going through the exact same thing at the moment, it's fine in heavy traffic but get up to speed and it heats up. Not boiled over yet but I'd say it's a similar thing to you with the viscous fan slowing at higher revs.

Got a couple of tubes of 10000 Cst silicon to do it this weekend. Will also give it a flush, new coolant, replace the thermostat and rad cap and see how that goes.

I agree with above, thermo fans won't pull anywhere near enough air alone, adding a push fan as well as the viscous fan like some models have may help a little but the original setup in working order is the way to go.

Thanks for the replies guys. By the sounds of it Ill be better off to stick with Toyota's fan clutch system. I think the only time Iv seen thermo's used have been on comp trucks that have rear mounted radiators.

I always thought that a fan was only working at low speed ???

Depends on the air temp flowing over it, with enough cool air flow I'm sure it does start to free up a bit.

In any case I found a pin hole in my radiator today

I think that what you'll find that came out of the fan was the viscous oil and not muddy water.

Here's a good article on doing a reco job on the hub.

http://www.zhome.com/ZCMnL/tech/FanClutch/FanClutch.htm

Was muddy water for sure, it poured out when I sperated the 2 halves. You could see the water sitting on top of the oil in spots as the 2 don't mix.

I have ordered a new clutch fan and will be ordering thermo's for the front of the radiator just to test them out and to see how how they last with river crossings and bog holes. Ill post up my findings in a few weeks.

hm...

Wish I had seen these posts earlier...

I have had a bit of experience with the toyota cooling system and the fan clutch.

Usualy (in most cases) a fan clutch problem causing an overheat is more at low speeds than high speeds... ie. low range work on a hot day at slow speeds - but not all the time.

The new clutches from Toyota are blue in colour.

They are adjustable.

They are refillable also.

The problem is - as I found out - they are not all adjusted the same.

I only changed my fan clutch as preventitive maintenance - I didn't actualy have a problem. Changing the clutch actualy gave me a problem because it was not adjusted properly. I have read on U.S. forums that not one out of 10 tested were adjusted correctly - all were different - out of the box.

I did a write up on my process that I did of adding new Toyota Fluid to it... I seem to have fixed the problem - although it hasnb't been hot weather yet... while towing - but it seems to be behaving like it should according to the FSM at this stage based on my temperature gauges on the top radiator hose and at the thermostat etc.

You can read the writeup here...

how-to-top-up-your-fan-clutch-and-do-the-blue-fan-clutch-mod-t1160.html

Personaly, I would not have recommended a new fan clutch unless it was stuffed. I would have just drained and refilled with Toyota Fluid unless the seals were stuffed - none of the parts are able to be purchased individualy - which means you would then be foreced to buy a new clutch anyway...

A Word of warning - DO NOT rely on the Temp gauge on the dash - do not think just because it is not moving past half way that the clutch is now working properly. The temp gauge on the dash has a big deadspot. That's why I have a digital gauge that tells me the real temp - and believe me it moves around a lot - yet the dash doesn't - if you do a search on my posts on the words "temp gauge dead spot" you should findd the info.

Hope this helps, if you have any questions, do not hesitate to ask...

Frank