I've got 2 I'm messing with
PN 3462180
no spring on the outside, so I assume this is the style of fixed clutching and no matter how hot it gets it doesn't change speed?
~20" 7 blade fan, pretty good pitch to it

PN 2705463
with the bi metal spring
18" 7 blade fan, looks a little less aggressive on pitch
I tested this one with my hairdryer, could only get it up to about 180* on the bi metal and ~150* on the clutch body, seemed like maybe it got stiffer but didn't lock up. Do they ever lock completely up and how hot do you have to get them?

Is there any harm in putting the bigger fan on the bi metal one or do I risk that fan being too much leverage and slipping the clutch and ruining it?

I ask because I'm still struggling to keep my charger cool in slow traffic. changing from elec fans to a 5 blade factory fan definitely has helped but the temp still creeps up if I'm stuck crawling.


https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2318928.html#Post2318928

Put a shroud on it.

I haven' found one yet that fits my universal cross flow rad and a mechanical fan, suggestions are welcome.

the 2 fans are
small one 2863210 (though I can't find any google results for this)
big 3462149

No way to test a fan clutch...even the FSM says if in doubt replace with new.

you need a shroud as said,, do you have the wide rubber underhood strip that fastens to the hood to seal off the radiator?, on mine I covered the core support instead, it is to keep hot air from going from the engine compartment to the front of the radiator.

No I tried searching for the hood strip, anyone got a part number for it?

You realize that universal means fits nothing?

Till you get a shroud you will continue to fight this.

My suggestion is trash the universal radiator and put a stock replacement radiator with a stock shroud back in it.

The primary aftermarket manufacturer states the following about that their fluid drive (viscous) clutch units:
1. Turn slower relative to engine speed than thermal drives
2. Not to use use as replacements for Heavy duty.

Looking at '69 Dodge Service manual, all A/C equiped V-8s got a thermal clutch. Only the non a/c 340 (a-body) and the 440 manual and 426 (b-body) got "torque" only fan clutches. So by inference, its probable that the factory thermal clutch provided higher fan speed at low rpm (when hot).

From the same manual, in B bodies with 383 or 440 got fans a bit larger when equiped with a/c and thermal clutches;
18.5" dia, 7 blades, 2.5" pitch.

It would seem reasonable to expect the thermal drive unit to handle an 18.5" fan as given in the FSM. To be a little more certain, see if you can figure the application of the p/n through by looking in some late 60s/early 70s parts books.

For a fan shroud, which will help radiator efficiency at low speed, probably have to make one or modify a generic one.
Here's nice thread on making a composite one (fiberglass).
http://www.ifsja.org/forums/vb/showthread.php?t=159476
US Composites mentioned in that thread is a reliable company to buy materials from - I use them for most of my epoxy materials.

And here's a nice thread on making a metal one.
http://www.ifsja.org/forums/vb/showthread.php?t=182997

yea, I also own a full size jeep.

In our parts loft I found a new thermal clutch and 5 blade. I put the 7 blade fan on it and low speed cooling has improved vs the 5 blade fixed

A factory clutch fan will have more drag when the car is hot when you spin it. No real test but I have spun many over the years and if you get the eng at about 100 to 120 degrees and spin the fan it should spin pretty freely. Then get the eng to 180 or up to 200 and it should have alot of drag on it when you spin it by hand. But you have to run the eng a little even to test it cold because the fluid will be thicker when the eng is cold (before started) since the fluid is cold at room temp the fan will feel to have some drag when you spin it before starting the eng in the morning. When I would start them in the shop I could here the fan spin on a cold eng for a minute or two until the fluid viscosity thins out to normal. Then in a minute of so I could hear the fan slow down and stop spinning much. If I let the car run up to about 180 to 190 then I would hear the fan kick back in and draw air. Also in the summer in my 1983 Ramcharger with a 318 when driving a 130 miles on vacation if I came to a redlite and sat a few minutes when I got to 60 mph it sounded like I was still in second gear because at the redlite with no air going through the rad the thermal unit in the fan engaged the clutch fan and once I got up to speed the fan was engaged and sounded so loud it made you think the eng was reving alot. But after about 30 seconds to a minute the air now going through the rad would disengage the clutch fan and you could hear it as it sounds like the eng slowed down at 60 mph. All the factory fans I worked with used a thermal switch and were temp activated. I think many or most aftermarket clutch fans are not temp activated and only work by rpm. Ron

If the fan clutch is working, you can hear the roar of moving air, especially in a closed area like a parking garage. But you may need to be out of the car with an assistant operating the accelerator to hear it properly. If the clutch isn't working, all you hear is the noise of the engine, not any sound of moving air.

66 Satellite with 413. 26" radiator, hemi-6pac fan. Heavy duty fan clutch from NAPA for rv's etc. Can't make it get hot even in parades at 90 + temps.

You can test a thermal unit to see if it still works. You have to lift the outer end of the thermal coil out of the slot and rotate it to the side of the clip. Sorry, I can't remember which way. Then run the engine for a minute or so and shut it off. The fan should turn by hand with stiff resistance if it is working. If no resistance after moving the coil to either side of the clip, the unit is a goner. I started my engineering career with the supplier of fan drives for Chrysler, and helped develop these products.

also ran across this thread...

https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/showflat/Number/7303922/site_id/1

with the fan on the car the test I was always told was to just watch for the fan to immediately stop with the engine if it was up to temp. I was trying to test a used unit before bothering to put it on the car. This new one passed that test. It's hard to hear it inside the car over the 3" exhaust, but it's doing something (more) than the fixed 5 bladed did for cooling and a lot more than the electrics+shrouds I did have on it.

Interestingly, I tried the factory thermo clutch vs flex fan on my Fury 15yrs ago and the flex fan was noticeably better in rush hour keeping things cool. The clutch had probably gone bad.