chef ar

The 66 big block ran hot enough that it puked anti-freeze on the ground out of the overflow hose and it took 45 minutes for it to get cool enough to refill. I changed the thermostat and it hasn't overheated, although the temp gauge says between 220 and 230 at the edge of the yellow. How can I tell if the fan clutch is bad? Thanks.

Chef AR

knight37128

Spin the fan.

How much "resistance" is there?

Kensmith

Run the motor and watch the fan. If you have a Thermo type, let it get hot, turn the motor off, see if the fan will spin. If it does, bad clutch. I just replaced mine. Big difference. It should be difficult to turn when it is hot after running the motor.

JohnZ

It should have significantly higher resistance to turning when it's hot than when it's cold. The thermo coil on the front reacts to the heat of the air coming through the radiator, so check it "hot" immediately after shutting it down from a hot idle before the thermo coil starts cooling down.

chef ar

With a hot engine, the fan will spin probably 2-3 inches if I wing it by hand. Doesn't have much resistance, though.

richbopp

Now compare the "hot" spin to a "cold" spin. If the hot is 2-3 inches and the cold is 7-8, then you have some resitance, but maybe not enough.

chef ar

I just checked it. No difference between hot and cold engine. If I spin the fan blade at 12:00 straight up clockwise, the second blade to the left will go to the 12:00 position. But even with the engine hot, I can spin the blades all day long with one finger. How hard is the fan clutch to change?

korvette kenny

Remove the fan & clutch assy from the engine. Then the fan unbolts from the clutch. 4 bolts, no big deal.
Hope it works out well.

JohnZ

When you re-install the fan clutch, it helps to make a 5/16"-24 stud about 5/8" long, screw it into the water pump hub, put the pulley and clutch flange over the stud, then install the other three clutch bolts, then replace the stud with the fourth bolt. The stud holds the parts in alignment while you put the "sandwich" together. Don't make the stud any longer than 5/8" or you won't have enough clearance to remove it.

dmentzer

Does anyone know who can rebuild an original fan clutch?

62Jeff

Paragon lists it in their on-line catalog.

chef ar

Thanks to all.

Chef AR

Joel 67

Fred Oliva is highly regarded in NCRS/Bloomington circles, and is consequently very busy (i.e. don't expect quick turn around).

http://www.gate.net/~foliva/

In my opinion, I would use the current GM replacement clutch 3916141. It is very similar in appearance to an original clutch and would cost a point or so in NCRS judging. You could probably buy this clutch for around the same cost as a restoration of an original clutch.

Rebuilding a used clutch is to me a risky proposition. If that thing grenades on you at the least you will have some things banged up under the hood, and potentially you will get a nice ventilation hole thru the top of the hood.

Moz Ray

I just bought a replacement fan clutch (GM# 3916141) from Paragon last Thursday for my '65 327/350 with a/c! I have looked and looked everywhere for a restored original, but nada. Will have it today.

By the way Joel, thanks for the advice . . . now I'm very glad I bought a new one.