ksig4runner

Ive noticed lately that my fan stays on a lot. i thought it was the fan clutch but i replaced it and it still does it a little. is this because of the sacramento heat (usually about 90-100) and my cooling system needs maintenence i.e. new coolant or something else?

superjoe83

thats normal, I'm guessing that you are using your a/c, that will make in engage more

Robinhood150

This is your stock fan, right? It's always going to turn a little, no matter what. It's a viscous coupling. When the engine gets hot, the fan turns even faster.

ChickenLover

Mine's running a lot too this time of year, it's normal. Does anyone know of a way to disable the clutch fan? It seems like if I were to find the wire that tells it to spool up I could put a switch on it and turn it off when I needed to. Anyone know where to look?

Robinhood150

It's a viscous coupling, purely mechanical, no electrical.

ChickenLover

That figures. When that thing engages it feels like it robs half my HP. How does it know when to engage itself?

mike_d

it's a viscous coupler filled with a silicone oil. when it gets warm the oil polymerizes and its viscosity increases. as it gets thicker, it trasfers momentum from the water pump drive shaft to the fan. as the fan pulls air in over the radiator the temperature decreases. once the temperature decreases enough the viscosity decreases and the fan is no longer coupled to the drive. then with the fan not running (and if you're moving slowly - usually less than 20mph) the lack of air will cause the engine to warm up, the radiator gets hot, the heat from the radiator gets transferred to the fan clutch, the viscosity of the oil increases, and the fan turns on. this cycle continues forever.

note: since both the water pump and the fan are driven by the same shaft, it's usually a good idea to replace both at the same time, otherwise there can be extra vibrations that cause premature wear.

ChickenLover

Great post Mike. I was totally in the dark when it came to the operation of that damned thing.

pedro_arg

Just one question: When the engine has not been used for some hours, i.e. its cold, is the fan supposed to turn freely? Tried to turn mine around today and still seamed to be somehow engaged.

mike_d

yes and no.

try this: when the engine is cold, try to turn the fan. then warm up the engine to operating temperature and then shut it off. the fan will be harder to turn. (this is the classic way to diagnose fan clutch problems)

the silicone is still fairly viscous when cold, so there will always be a little coupling of the fan to the drive (the fan clutch is never at 0% or 100%, but somewhere in between depending on engine temp). also, i've noticed that when you first start the engine, even if it's cold, the fan will turn for about 10-20 seconds or so. my guess that when nothing is spinning the oil is a little more viscous so the fan will start spinning with the engine and then it'll start breaking up the oil molecules and go back to normal operation.

pedro_arg

Thanks Mike. Will try that in the morning.