Thermal or Viscous? Clutch fan.

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Bronze Barracuda

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Hello. Could anyone help me identify if this fan is a thermal or a viscous clutch fan? Also how would I test it?
Thanks.

PXL_20211215_013254326.jpg
 
The fact that it has one of those thermostatic spring coils on the front makes me think it's thermal...
 
The fact that it has one of those thermostatic spring coils on the front makes me think it's thermal...
Yeah that's what I was thinking after I posted it. I just picked it up an hour ago, took a picture without my glasses on. Only when I viewed the post did I notice that. Still I suppose it could activate by centrifugal force? IDK. Trying to figure out how to test it, don't want to buy a new clutch if this one is good, or if they're serviceable.
 
It's a viscous clutch fan with thermal control. So yes, it's both.
 
It's a viscous clutch fan with thermal control. So yes, it's both.
Oh it must've transitioned from thermal to viscous. Seems about right for this day and age!
But seriously, that's how they work eh? Good to know. Would you know if there is a way I could test it, for proper function?
 
I can't think of a good bench test.
On the car, with cold fluid it should be hard to turn.
As it warms up it will get easier to turn.
When it gets Hot, it will again get hard, probably very hard to turn.
 
I can't think of a good bench test.
On the car, with cold fluid it should be hard to turn.
As it warms up it will get easier to turn.
When it gets Hot, it will again get hard, probably very hard to turn.
Maybe a heat gun pointed at the thermal spring?
 
Maybe a heat gun pointed at the thermal spring?
I don't see it, the housing and the fluid need to go thru the temp change. You can use the IR to pin-point when it happens but that is all. And I don't see a good reason to know that; as long as it does in fact go thru the changes.
 
Is it leaking oil? If not, it's probably good.
Clean it up.
I cleaned it up a bit. Hard to tell if it was leaking or not. It was covered in old dust. I cleaned up the thermo spring, and put a heat gun to it and the spring worked also was able to move the valve that the spring is attached too.
 
I got rid of a fixed fan, got an old Mopar fan clutch from a friend. Cleaned it up, installed it and it started leaking from the rear. Replaced it with a Hayden # 2947. The Hayden is 1/4" longer. Needed a radiator anyway, so went back to a cast iron pump that is 3/4" shorter than the aluminum pump.
 
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Oh it must've transitioned from thermal to viscous. Seems about right for this day and age!
But seriously, that's how they work eh? Good to know. Would you know if there is a way I could test it, for proper function?
No, no transition involved. It is what it was made as. All of those type clutches are viscous. Some have thermal assist and some do not. Most of the heavy duty units have the thermal spring. As the radiator heats up, the hot air caused the thermal spring to coil and turn the control valve inside the clutch and cause the clutch lock up even more. They can lock completely up if enough heat is generated. "Viscous" only refers to the viscous fluid (usually a silicone compound) inside the clutch. So both styles are viscous, but one has the addition of a thermal spring that aids in additional lockup as heat increases. The fan in the picture above is a viscous clutch fan with thermal control. There are standard viscous clutch fans that do not have the thermal control, but both are viscous clutch fans.
 
I cleaned it up a bit. Hard to tell if it was leaking or not. It was covered in old dust. I cleaned up the thermo spring, and put a heat gun to it and the spring worked also was able to move the valve that the spring is attached too.
Turn the fan at room temperature and get a feel for how much resistance there is. Now gently heat it with a heat gun and see if that resistance gets greater. As heat is applied, the fan should get harder and harder to turn separate from the clutch.
 
Turn the fan at room temperature and get a feel for how much resistance there is. Now gently heat it with a heat gun and see if that resistance gets greater. As heat is applied, the fan should get harder and harder to turn separate from the clutch.
Yes, good idea. I'll give it a try on the weekend.
 
I got rid of a fixed fan, got an old Mopar fan clutch from a friend. Cleaned it up, installed it and it started leaking from the rear. Replaced it with a Hayden # 2947. The Hayden is 1/4" longer. Needed a radiator anyway, so went back to a cast iron pump that is 3/4" shorter than the aluminum pump.
I thought the 2947 Hayden was the shorter style??
 
They probably are shorter, but the Mopar clutch was 2 1/2". The #2947 is 2 3/4". Do not know if there is something shorter on the market. Thing is, 1/4" here and there with radiator differences make a difference.
 
BTW, viscous fan clutches should be stored in the same position that they are intended to operate.
 
Can not answer to that comment, but I would bet that they don't ship from the factory like that. No placarding on box to that effect. Having said that, if you lay a refrigerator on its side, you are supposed to wait 24 hrs before plugging in to power?
 
Can not answer to that comment, but I would bet that they don't ship from the factory like that. No placarding on box to that effect. Having said that, if you lay a refrigerator on its side, you are supposed to wait 24 hrs before plugging in to power?
I have seen it on the box.
 
I guess thats old school technology. I just did some reading and the newer clutches (seals) dont care. :thumbsup:
 
Wheeler Dealers showed how to test a viscous clutch. Ed China (original tech) grabbed the fan blade with a thick leather glove while the engine was idling. I think he said if the viscous clutch was good he wouldn't be able to hold on. Perhaps the metric is to count fingers before and after. Less fingers after means "good clutch"? A thermal type should have more drag as the air from the radiator gets warmer. Even with the thermal sensor, the fluid (silicone?) might get more viscous as it gets hotter. Perhaps a better method is to turn off the engine while hot and see how easy you can spin the fan. If hard to turn, the clutch is likely fine. If it freewheels, definitely bad. Perhaps some mechanics watch the fan blade vs engine damper as they turn off the engine to judge.

Some people on my M-B diesel forum have fussed with the clutch-fans. BTW, those fans (1982-85 300D or SD, probably other years and engines) will bolt to a Mopar water pump (same hole diameter and 4 mounting holes). It is much thinner, so I thought of using on my 1964 225 engine, but still not enough room before the radiator core. The nylon fan blade is nice. Another thin clutch-fan is on older Jaguars (I recall some here have used). Anyway, those have a flat thermal spring which acts on a little valve underneath, which you see when you pop the flat spring off. Some guys found the proper silicone fluid to refill the reservoir w/ syringe since it can leak out (perhaps stored flat like someone here said). I haven't read of a Mopar owner doing similar, probably since new clutches are easy and cheap. Likely there is a way since "if built by man, a man can fix it" ("just a question of price").
 
... if you lay a refrigerator on its side, you are supposed to wait 24 hrs before plugging in to power?
The thermal absorption type (ammonia solution) used in RV's are very finicky. If the RV isn't parked close to level, the fluids in the absorption system can get in the wrong place so it no longer cools. I had one that didn't work (Dometic), so left it upside down for 6 months and other ideas that supposedly could restore it, but no luck. Since a new cooling assembly cost $700 or a Chinese fridge $500, I kicked it to the curb (rebuilder took it via "free stuff" cl ad). I put in a small 120 VAC "dorm fridge" which fit perfect ($180) and added 1000 W inverter ($120) to run off 12 VDC trailer battery or vehicle when no shore power, which is how RV's come today. Then fixed all camper trailer problems by selling it since wifey refused to use it and needed the parking space for my too-many cars. Haven't given up on the old Mopars, though wifey doesn't appreciate either. Offload wifey? No, since she hasn't yet fussed about my fishing (a country song).
 
Is there a fan clutch shorter than a 2947? I thought that was the thinnest. I don’t know how you would get the bolts in if it was shorter. I had a heck of a time getting my 2947 installed because how short it is.
 
The factory drive on my '72 Dart was 2 1/2", it had studs in it. Classic Industries has an OEM for about $170. Do not know if it is 2 1/2". I had to replace it, leaking oil. Hayden #2947, yes, you have to learn how to get it on, tricky!
 
The factory drive on my '72 Dart was 2 1/2", it had studs in it. Classic Industries has an OEM for about $170. Do not know if it is 2 1/2". I had to replace it, leaking oil. Hayden #2947, yes, you have to learn how to get it on, tricky!

Interesting, do you have a part number for your 72 clutch?
 
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