Testing the 3B viscous fan clutch?

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Feb 27, 2008
Las Vegas - Nevada
I have been reading some of the posts that discuss the benefits of one fan type over the other, but have not found a reference to testing the function of the fan clutch.

My assumption is that I should drive for some time and let heat build up, then pull over and with the engine stopped spin the fan - if there is resistance (how much?),:grinpimp: then my clutch is working? IF not, then my clutch is shot?:frown:

It has been in the mid 90's to 100's for the past few days here in Vegas - should my clutch engage at a particular temperature?

My engine temp was up around 190deg F while moving it on the freeway - doing about 75-80 :steer:(?) (Hard to tell exact speed with the bigger tires and floating speedo.) I haven't tested the fan HOT as of yet, but when its cold it spins freely.

I have my fingers crossed that my fan is working - though after pushing the beast up some good hills I do see the temp go up (didn't have a real gauge at the time) but it gets into the 2/3 region of the stock gauge. This is running about 12PSI of boost. (gauges are nice to finally have).

BTW: My radiator seems fine - though a new cap wouldn't hurt. :hmm:
The fan only works at lower speeds,probably under 40 kph.
The amount of resistance should be enough so you cant free spin it and I think it should be like that when its cold also.

Do you have a EGT gauge? That "pushing the beast up some good hills" is probably pulling some very high temps in the combustion chamber
Rosco, I have Pyro gauge mounted at the elbow- post turbo to down pipe. My fuel is set not to exceed 1150F.

So when cold the fan basically free wheels, and at operating temp and up I feel resistance. Yesterday after getting the motor up to 200F on the freeway, slight uphill, movin about 75-80mph, Boost 8-10psi, EGT 800F.

So I guess it is working somewhat, but I have never felt a new vicous clutch in action so I have no reference point.
I just checked the clutch fans on both of mine ,7.30 am and 9c and they are both stiff to turn when cold
One of them has only done about 25000klm.
I guess yours are still working but heading for replacement.
There is a heat sensitve spring that tightens up and provides more airflow the hotter the engine gets

To understand them better look for bigbrowndog's fan clutch rebuild.
You can replace the spring and the silica oil.
Good call on the thread - I will look for it!

Have a good one!

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