Thread: Fan interruptor switch.

I read here somewhere someones ac fan failed after a river crossing.
I was told the reason most 4wds have viscous fans was the fan will can tolerate water as they slow down with water resistance.

Better still remove the viscous fan or belt before crossing?


4x4 and a Water Crossing - Treading Water Offroad

The Radiator Fan
Inspect your radiator fan. Take note of type of radiator fan you have. Most 4x4's have a viscous coupling type fan, also called a clutch style fan. These fans do not spin at full speed when the engine is cool and can be a benefit when encountering a water crossing. You may also find that you have a fixed type fan that always spins at the speed of the engine. To check your fan turn off the engine and try spinning the fan. If the fan turn easily with the engine off and there appears to be a clutch mechanism at the center of the fan this is most likely a clutch type fan you will probably can get away without taking off the fan belt. If the fan doesn't turn easy or it is definitely the fixed type fan, then you should consider removing the fan belt before entering a water crossing. The reason is when a fan encounters water, it acts much the same way as a propeller and a light-weight radiator fan will flex opposite the direction that it blows air, which is towards the radiator. With most engines having little clearance between the radiator and radiator fan, this means you may see contact as the fan bends, possibly slicing into and damaging your radiator.

How does the tarp help? is the radiator actually being forced back into the fan by the weight of the water? What makes contact with the rad the hub or fan blades?

Thanks

I was under the impression that the blades bend from impact with the water and slice up the radiator. I'm guessing that the tarp, when fitted properly, will stop water from hitting the fan.
I may be wrong.
Cheers
Muppet

the big problem is the first inrush of water....

blurb enough water in fast enough and the radiator will flex back in its mounts, its ment to do that, thats cool.

put enough water into a fast enough moving fan and the plastic blades will pull forwards, thats ok, they're ment to do that as part of maintaining a constant air velocity through the radiator....

hang on...

two objects moving towards each other within a range of tolerance? yeah sure the engineers would have thought of that... what they didnt count on was some knuckle pushing the boundries by using a medium thats on the order of several hundred times as dense as the one the gear was designed to work with.... Lets also throw in, dodgy engine and gearbox mounts that allow the inertia of said engine and gearbox to move the fan closer to the engine when you yahoo it into the water removing even more of the engineers design clearance.

the primary reasons for tarping (in no particular order) are.

1. it reduces water flow through the radiator protecting its cores and fins
2. it reduces the water level in the engine bay initially allowing the fan time to slow and stop by means of drag (its still going to flick water around)
3. it prevents a sudden rush of water coming back into the engine bay drowning your engine if you happen to drop a wheel into a rut or obstacle, buying you a precious second maybe 2 of engine run time or shutdown time
4. it provides resistance to the water promoting the propogation of your bow wave IF you do it right