Knowing almost nothing about things mechanical, can someone please tell me what a viscous fan is?

The reason I ask is I have an Australian Ford falcon, 1994, which overheats intermittently. Usually in heavy traffic or stopping at lights. Up goes the temp to the top of the normal range. Get back to cruising speed and it drops again. Doesn't use coolant. I'm pretty sure it's not just the temp gauge as lots of heat from the engine at these times. Someone tells me it may be the fan. But the fan is spinning.

Anyone any ideas?

 

Uses a viscous fluid controlled by a valve that opens or closes to lock or free spin the fan. The valve is controlled by a bi-metalic spring that senses the air temp coming off the rad.

The only test that I know of can be
DANGEROUS!!!!

Perform at your own risk....with the temp up high take a piece of heavy cardboard and at idle try to stop the fan. If you can it's NG it should be locked under those conditions

Larry

 

if its like a reg clutch fan you can check it by this way. when engine is warm turn motor off then try to spin fan with one quick spin if fan turns more than a full turn its bad.

 

OK, did what you said and the fan appears OK. So what now? Thermostat? Radiator? New car?

 

We don't get the Falcon here in the States, so we won't be much help on specifics.

But the usual questions still apply, such as when was the last time the coolant was serviced? Sounds like it hasn't seen service in a long time.

 

Actually the coolant was replaced only 3 months ago, due to a hose blowout. The blowout did the draining, I did the replacing. Also had all hoses replaced at the same time. I was thinking thermostat but not sure. what do you think?

 

Did the car overheat?

 

I assume you mean did it overheat when the hose blew. It did get hot, but I stopped it right away and had it towed home. Don't think it was hot enough to do any damage.

 

it wouldn't be thermostat . take off radiator cap off when cool let the car warm up so thermostat opens see how the radiator is flowing it might be partially clogged. is the fan shroud in good shape. hold hand in front or radiaotr you should feel a draw of air while it is running. is the grill in front of radiator open some cars like the camaros have a like an air scoop under where the bumper is that draws air to the radiator if its not there it will run hot.