Visco Fans and how are they supposed to work

VerMonsterRV

Gotta Be Nuts
In my quest to completely understand the cooling system on our 1120 I am pondering the visco fan. Why? Well a strange thing happened yesterday while essentially idling down a 10 mile gentle sloped corrugated dirt road. 3rd gear left the revs pretty low but with enough braking to slow the truck. Well we are now in Arizona and the temp was in the 80's f. For the first time the engine temp rose higher (not super high, just above normal as I watch the temp now like a hawk due to our radiator issue) than I have ever seen and the visco fan did not engage. So, we stopped and pondered things a bit. Then we decided to not head out on any remote roads and drive the 20 miles downhill on pavement to a formed campground (and internet). So heading downhill since the engine was running a bit hot I put the truck in neutral and turned on the cab heater thinking that would help (remember this is my first vehicle without an electric temp controlled fan). Well of course the revs were low and old visco would not engage. Then I sort of had an idea, put the truck back in gear to get the revs up and turned the cab heater off. Low and behold the visco fan engaged and engine temp went right back to normal. So I turned around and drove back up the hill and all was ok. So I know the visco fan has some oil in it for it to function and is separate from the actual engine coolant temp. So, long story short, should the visco fan engage even when the truck is sitting at idle? Or is this just how they work? If it should engage at idle could the oil be low? Would there be any adjustment?
 

Sitec

Adventurer
In my quest to completely understand the cooling system on our 1120 I am pondering the visco fan. Why? Well a strange thing happened yesterday while essentially idling down a 10 mile gentle sloped corrugated dirt road. 3rd gear left the revs pretty low but with enough braking to slow the truck. Well we are now in Arizona and the temp was in the 80's f. For the first time the engine temp rose higher (not super high, just above normal as I watch the temp now like a hawk due to our radiator issue) than I have ever seen and the visco fan did not engage. So, we stopped and pondered things a bit. Then we decided to not head out on any remote roads and drive the 20 miles downhill on pavement to a formed campground (and internet). So heading downhill since the engine was running a bit hot I put the truck in neutral and turned on the cab heater thinking that would help (remember this is my first vehicle without an electric temp controlled fan). Well of course the revs were low and old visco would not engage. Then I sort of had an idea, put the truck back in gear to get the revs up and turned the cab heater off. Low and behold the visco fan engaged and engine temp went right back to normal. So I turned around and drove back up the hill and all was ok. So I know the visco fan has some oil in it for it to function and is separate from the actual engine coolant temp. So, long story short, should the visco fan engage even when the truck is sitting at idle? Or is this just how they work? If it should engage at idle could the oil be low? Would there be any adjustment?

 

VerMonsterRV

Gotta Be Nuts
Believe it or not, I actually read that article this morning. I don't think I have ever heard our fan come on at idle, but then I rarely let the truck idle for long periods. The hub needs to heat up in order to start to spin, plus I would assume RPM also plays a role. Any idea if the oil in our fans ever needs changing, is it even possible and are they at all adjustable for temp?
 

Recommended books for Overlanding

999 Days Around Africa: The Road Chose Me
by Dan Grec, Dan Grec
From $19.95
Adventure Motorcycling Handbook: A Route & Planning Guide
by Chris Scott
From $48.88
Tortillas to Totems (Every day an Adventure Book 4)
by Sam Manicom
From $9.99
Road Fever (Vintage Departures)
by Tim Cahill
From $6.99
Deep Survival: Who Lives, Who Dies, and Why
by Laurence Gonzales
From $9.99

Sitec

Adventurer
Believe it or not, I actually read that article this morning. I don't think I have ever heard our fan come on at idle, but then I rarely let the truck idle for long periods. The hub needs to heat up in order to start to spin, plus I would assume RPM also plays a role. Any idea if the oil in our fans ever needs changing, is it even possible and are they at all adjustable for temp?
The ones we've changed on tractors are a throw away unit. Never had one apart, but have locked quite a few up on tractors that are working hard on 35 and 40 deg days. They need all the cooling they can get!
 

Neil

Observer
Our Viscous fan has never come in at idle, even after hours.

The only time it comes in is on long inclines in a low gear. Surprisingly the gauge only has to climb a little for it to come in, we hear it. It does it's job and soon disengaged.

Interestingly, on the back of our fan is a large nut , 19mm ish. I know that by turning this 180 degrees it locks the fan on so it's permanently engaged. I guess this is for instances when you think you have lost the fluid.

Never used it so it, probably never been turned in 31 years so it could be seized up.

Neil
 

part time nomad

Adventurer
Neil is right! you can lock the fan up with that nut if you need too, but it will hit the fuel economy! but better than overheating.
Also some have 2 little sliding tags to lock it up with. They are normally sealed units, but if ever you remove/ fit one they must remain in an upright position.
 
Top