Tying up the 4WD viscous fan for crossing waters?

All I know is if you have a viscous fan you can tie it up during a crossing which reduces damages to radiator core.

How can a dummie know is the fan is viscous?

If it is viscous is the fan going to just snap the tie? Or damage fan unit from not spinning under load from motor?

We would need to know the make and model to tell, most modern vehicles will have electric fans due to fuel economy standards.

A slow steady rate you should not have any real issues with stock fans, and in my very limited experience overheating would be a higher risk with a stopped fan. Or hydro-locking if you happen to get enough water in the intake.

If you are going fast often in race like conditions relocating the radiator is a good idea.

For mechanically operated fans, there are several different mechanisms for the fan clutches. Some are air operated. Some are spring operated. The viscous fan clutches have a silicon based liquid inside.

I’m an electrical engineer, not a mechanic, but all of the viscous fan clutches that I am familiar with have a bi-metallic coil on the front of them. When the fan is cool, the silicon fluid settles into a reservoir and the bi-metallic coil keeps the reservoir closed. When the engine heats up, the bi-metallic coil expends and opens the reservoir, releasing the fluid and operating the clutch.

On the ones that I am familiar with, if you remove the fan shroud so that you can see the front of the fan, then you’ll be able to see the coil on the fan clutch.

I have no idea if tying up the fan for any of the different types of fan clutches will cause any damage to the fan or the clutch mechanism. I would expect the spring type to be damaged, but a viscous or air operated fan clutch might be ok if it is locked/tied into place.

If the engine has a viscous fan you can grab the blades with the engine off and turn them. They spin in the hub. Normal blades cannot turn, they are always locked to the hub.

But how would it prevent damage to the radiator if you tie them? A fan should not hit the radiator under any circumstances.

Viscous fans are only installed on longitudinal engines where they are driven directly from the engine. Most car today use electric fans.


When fording deep water, the fan operates underwater, rather than in air. Since water has rather a higher density than air, the forces on the fan blades are proportionally higher. This can produce enough force on the blades to bend them into the radiator.

If you doubt this, compare the size of the foils on a heavy, relatively slow hydrofoil vessel to the size of the wings of much lighter, much faster airliner.


On my dads classic, which had a viscous coupled radiator fan, we replaced with an electrical one with a thermostat. Had some advantages namely it had a higher RPM so it could move more CFM if in traffic or the like.

Looking on Amazon, there are electric, IP68 rated, radiator fans: http://amzn.to/2BxlZZo The advantage of that guy would be you could either have a float sensor that when the water level is approximate to the top of the lowest blade it turns off, or, you could have a toggle switch in the cabin.

However, thinking about this more, where is your radiator fan located? If it is viscous coupled, it’s probably behind the radiator. You won’t run the risk of bending the blades into the radiator but rather the engine and anything else. Or, you’ll warp the blades in such a manner that they’ll hit everything.