Machanical fan

[koditten]

School me on how a machanical fan works. For the life of me I can not figure out why the fan will bring in more air when there is a demand for cooling. Why does the fan stay engaged when you start up a cold motor. It seems that the fan would free wheel when everything is cold.

A second question, is it true that you can not let a fan clutch sit on its side, it has to remain in the verticle position?. I always thought this one was BS, but I wanted to ask anyways if anyone else is aware of this wives tale.

Willing to learn

Later
KO

 

[eldirector]

Read up on viscous fan clutches:
http://en.wikipedia.org/wiki/Fan_clutch

Basically, the clutch is filled with a liquid. At cooler temps, the liquid is less viscous and will let the fan spin more freely (turns slower than the engine). At higher temps, the viscosity increases, causing the fan to "engage" more and turn faster.

Never heard the "wives tale". I assume some fluid-filled clutches could leak, though.

 

[kbs2244]

Well, there is often a shortage of wives in garages.

But not of the equivalent “old-timers” tales.
They are right.

Keep the fan upright for at about 24 hours before installing.
It lets the oil settle.

 

[Lotek]

I wouldn't worry about it too much, as soon as you start the motor, the fluid balances out, in fact the big whir that you hear from the fan on a cold start is the fluid equalizing. Call it an old husband's tale...

 

[jomobco]

Also keep in mind when you're thinking about the fan sucking too much air at startup you also have a thermostat to make sure you don't overcool and the motor heats up properly.

 

[Charles (in GA)]

The fan has a thermostatic spring controlling a valve inside. Initially the fan drives but after it gets spinning the thermostatic valve and centrifugal fluid flow causes it to disengage until the thermostat coil moves the valve to allow fluid to drive it.

Call it an old wives tale if you want, but all of the factory manuals I have, and the replacements I've seen, and molded into the clutch housing itself, all say to store in a normal operating position, and not lay flat.

Charles

 

[koditten]

Thanks,guys, that helps. I think. The clutch is engaged until the spring thingy tells the fluid to go to "free wheel" upon cold start up. Got it!

As for storing the fan verticle, it was just easier to hang on a nail and not worry about bending the plastic blades.

KO

 

[Greatbear]

In the past, I have always read and have been told to keep fan clutches either vertical or with the front end down (shaft up). If placed shaft down, the oil could migrate into the bearing and damage it. These days I have net seen much in the way of these warnings. I don't know if the designs of the clutches are more robust, seals are better, or whatever. When I take a fan off of a vehicle, I stand it upright or put it face down out of habit. New clutches mostly come in boxes facing down.