I've got a 71 Charger w/440, 26" radiator, A/C. The car seems to be running hot so I need to test the fan clutch to see if it's working. What is the quickest and/or best way to test it?
Thanks

It should offer significant resistance to spinning when it's hot....If when it's hot the fan spins easily on it, it's toast.

Thanks. I figured I'd be able to hear it too but I never have. Always sounds the same. I'm gonna try seeing how difficult it get to turn after a longish drive and everything is good and hot per earlier suggestion.
attaboy

Start up the motor, let it the clutch fluid circulate to where it is suppose to be. Feel the air behind the fan.

Put a piece of cardboard in front of the radiator to get the motor hot. Let the motor get hot. pull cardboard off. let hot air get to the fan sensor. As the clutch coil starts activating the clutch you should feel a increase in air flow behind the fan.

Note you will not get much air flow across the sensor when the cardboard there.

I rotated the fan while cold: Minimal effort required to get it to rotate. I warmed up the car until the gage read very hot(note that the fan spun even when I first started the car) and then I turned the car off: the fan rotated with only slightly more effort than when the motor was cold. The temp gage read very hot but the radiator really didn't seem overly hot to the touch (too hot to hold your finger on but not to touch for a second) and it was not boiling over. I'm beginning to think that the gage is bad or not calibrated well. I have a spare gage and voltage limiter so I think I'll hook that up to the sending unit and retest. What do ya think?
attaboy

I don't think anything is wrong with your gauge.
Did you try what HealthServices suggested?

Don't you think the fan clutch should be much more locked up if your gauge was showing hot? I do.

Is your fan clutch the type with fluid or the thermostatic spring on the front?

I think that it's the fluid type.

I also think that it should be MUCH harder to rotate the fan by hand when the car is hot but the fan is still easy to rotate. But then again, the car may not be as hot as the gage says and therefore the fan would still be easy to rotate by hand. I'll be trying the cardboard test later today and hopefully be able also to hook a second temp gage to the sending unit as soon as I locate my spare voltage limiter.

I don't think the fluid ones lock up and get tight when hot, engine off. They are centrifical so I imagine they must be moving to work. I have a fluid type that does as yours does and I have always wondered about it too.

Well, that would explain why the fan spins at cold start up. Maybe even explains why it didn't get "stiffer" after extended drive. I wonder what advantage this set up has over a regular bolted on fan? I'm still gonna hook up another gage to the sending unit. That seems like the best way to go at this point.

From what I understand, and I could be wrong, They free up horsepower by allowing more slippage than the thermal ones,which lock up tight once the clutch engages. This, I imagine lessons their overall cooling ability compared to either a fixed or thermal clutch type. I would like to hear what others have to say regarding the slippage of the fluid fan clutches

pop the hood and with the motor not running grab the fan try to give it a good firm spin if it makes a full rotaion its junk it should turn at most 1/2-3/4 turn
start it up let itrev it up a few times let it idle thenwhile looking at the fan shut it off it should stop if it spins morn then a turn or 2 after motor dies its junk
if its good the first one will tell you as most of mine only turn 1/4 of turn if trying to spin it when cold

Chally1, what type of clutch are you using?

Fan will spin by hand maybe 1/4 turn when motor is cold. About the same when the motor is hot and off. The fan does not keep spinning after motor is shut down. Sounds like the clutch is good based on these observations.
I've finished hooking up my spare gage to my spare voltage limiter. I'll be hooking it up to the sending unit tomorrow and taking the car for a drive. It'll be interesting to see what the spare gage reads.

the viscus clutch is for less HP/torque loss and less drag when revs go up fast

the thermo clutch is more for a HD cooling package and a/c

not running grab the fan and see if you can wobble it on the shaft side to side-up and down

if it wobbles its bad

look for fluid leakage around the shaft and clutch seal..if it leaks its bad

if its low on fluid from leakage it will spin freely and is bad

I use a thermo clutch and 7 blade fan and replace it every time I replace a wp

over kill..probly...over heating...never has

I think I'm switching to the thermal type as I can use all the help cooling in S.Fla. I can get.
I'll give up a few ponies to be able to idle cooler in traffic. Thanks for checking..

i ask for a thermo clutch for a HD cooling pakage on a 78 BB 440

then went to the JY and got a 7 blade fan from a amc hornet 6 cyl clutch fan set up

I also replaced the rad in the 85 truck with a 3 core HD cooling replacement rad..all brass no plastic

i have to bump the t stat up to 195 in winter to get a little heat

run a 180 in summer and it never goes over 190* in traffic

you can hear the fan cycle also when idling,takes a few mins and you hear it load up and roar blowing air on the engine side like it speeds up in rpms

few mins later it quites down and back to normal till the t stat opens again

I can watch the mech temp gauge move up and down with the fan

i also use a HD 5/8" shaft wp with 8 vanes with the non a/c pullys

the neck will have ribs down it instead of the gatlin gun holes around the shaft

if you have a/c pullys use a 6 vane wp

they will cavatate if an 8 vane is used with the smaller a/c pullys at higher rpms

a/c pully is samller and turns faster at idle to pump x amount of water with 6 vanes

non a/c pullys are bigger and turn slower with 8 vanes to pump same x amount of water at idle

match the correct parts and use new wp not a reman wp IMHO