1990 Townace Super Extra 2ltr diesel auto.
Q. Should the viscous fan turn all the time, even when the engine is still cold. Me-thought this type of fan only operated when the engine was hot. If only when hot, any suggestions as to what may be the problem with mine.

- (#13526) gordon davies, 28 Sep 04 15:00

"Should the viscous fan turn all the time, even
when the engine is still cold"
Yes, it will normally turn whatever the temperature of the engine. However, when the engine is cold, the fan will not turn at engine speed due to "slippage" in the viscous hub. As the temperature of the air, passing through the radiator, increases, a thermo sensitive device, on the front of the fan assembly, closes ports within the hub and gives more "drive" to the fan blades. If your fan only operates when hot, it shows that it is working but, possibly due to viscous fluid loss,wear within the hub,or a faulty thermo device, there might still be unwanted slippage at high temperatures. You can do the "cotton breaking" test, throughout the engine temperature range, to see if it is "driving" correctly when hot. There is information on this in the archives.

- (#13526) John Davies (Leics), 28 Sep 04 15:36

Cheers for the reply John. I did actually find the info. mentioned, shortly after posting the message. But what is puzzling me, is that just after starting the engine, I tried to stop the fan from turning ( NOT with my hand) but a soft piece of wood. There was so much viscous adhesion that nothing would stop it turning. Could this be a fault with the thermo sensor sticking, or possibly the "return" ports being blocked, or simply the fan a bit gunged up ? Any idea what sort of job is it to remove / test the fan?

- (#13526) gordon davies, 28 Sep 04 17:21

hello Gordon,

Are you sure the fan hasn't been bolted straight through the coupling, I do remember people saying that as a way of preventing overheating, the viscous coupling was bolted through making the fan turn despite what was going on in the coupling. This was decided to be a bad idea because the engine had trouble reaching it's running temperature. Have you had difficulty getting your vehicle up to running temperature?

- (#13526) Mark, 29 Sep 04 01:02

Mark could be right, as the fan should definitely be a lot more "free" in cold/cool conditions.
Fan blade removal is very simple. There are four bolts through the flange and the fan blades can be removed without the drivers seat removal, though this does make the job simpler as there is more space to work. These bolts also retain the pulleys so, slackening off the belts, via the alternator, is advised. The viscous hub assembly can be tested by hand and you will see the coiled thermo operating device on the front. Warming this (hairdryer) will show if the coil moves. This test will not really show if the hub starts to tighten up, as the fluid is passed through the internal ports by centrifugal force but, it will give you some idea of it's operation. Overhaul means dismantling the hub and replacing the fluid which, I understand can be obtained via the Toyota dealer. However, a s/h viscous hub might be the answer.

- (#13526) John Davis (Leics), 29 Sep 04 02:31

Been away for a few days, so belated thaks to all. Will probably dismantle hub and check the fluid etc etc before getting a replacement.

- (#13526) gordon davies, 5 Oct 04 17:19

The viscouse fan will be fully engaged for about 1 minute after initial start-up.

After that it should settle down to its normal pattern of basically free-wheeling until the temp goes up.

But for the first minute or two (maybe more over there if it is colder - I don't know?) it should give an audible roar and be very stiff.

- (#13526) DaveW, 7 Oct 04 00:08