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Viscous fan


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90 is now running again and all seems well though I'm still bothered by the viscous fan (which has some play in it, water pump is fine).

So before I wreck a perfectly good viscous with a drill and self tappers how can I test it to see if its good or not?

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The bearing can go separately from the viscous bit, we see quite a few at work that have bearing failures though I have seen some bad ones and have yet to see one come right off - which is the obvious risk, it comes off and starts chewing through the radiator :blink:

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Well made some progress today. Been running the truck during the week and warm up time seems ok but once its wam its just having trouble getting rid of the heat (heater blower helps).

Also the viscous fan is very very free when the engines hot so not doing much (and I've got the hi level bumber and 8274 blocking the rad). Though oddly when I went to it this orning the viscous unit is stiff with no play when cold?

Anyway fan removed and I can see back of rad is caked in mud so grill off as well and £3 down the jet wash gets a lot of mud out of the core. All back together and running great now, needle mid range, but I'm still not sure the fan is doing anything, stiff when cold and free when hot?

Did look at drilling it to lock it up but not having a clue what's inside I wasn't sure where's best. Anyone got any pics/tips?

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Think of the fan viscous unit as a torque converter. When the engine is off then there is no resistance through a torque converter as the oil is not being pumped against the vanes. Once the engine is running, the oil drives the gearbox and the car goes forwards. The viscous fan unit works in much the same way. When it is cold the oil is thick and the unit feels stiff - the oil may be thixotropic as it seems to get free-er as you turn, correct? Anyway, once the engine is running and the whole thing turning, it is able to do it's thing. As the engine gets hot and needs the fan to run fast, a valve opens (or closes) in the hub and the oil is made to drive the fan. Once the engine cools, the valve returns and the hub stops driving. Turn the engine off and it all goes loose again as there is no rotation to move it.

Clear as mud I guess. :)

Chris

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90 is now running again and all seems well though I'm still bothered by the viscous fan (which has some play in it, water pump is fine).

So before I wreck a perfectly good viscous with a drill and self tappers how can I test it to see if its good or not?

If the radiator is full of mud then there is not going to be much airflow and no airflow = no change in temperature of the bi-metal sensor on the viscous fan. Guessing you have V8 and it is usually the core inside which goes phut due to corrosion, so it might be a case of radiator rather than the poor old maligned viscous fan!

To test the fan take the truck for a good spin get it nice and hot, stop and leave engine running, open bonnet and put palm of your hand on top of engine facing fan, give engine some revs and if your hand gets blown to the bulkhead by lots of hot air it's working! I have never been able to tell from spinning the fan with the engine stopped whether a fan is good or bad.

If the viscous bit has stopped working use about a no. 8 self tapper about 1ins long and screw between the interface of the 2 halves on the engine side. Just about do-able with everything in place. Rotate 180° and put in another self tapper. The 2 halves are soft metal and the self tapper will screw-in quite easily and lock the 2 halves together.

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