How exactly fan clutch is supposed to operate?

superfragl

superfragl

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Hi folks,
I am not sure if I am getting it right. As I understand, a thermal clutch (the one with the spring) is supposed to lock or at least the friction should increase as the radiator temperatures increase. I purchased new HD clutch (from Autozone) and tested it with a heat gun. I heated it up to 180* but it only got looser. Is this normal??
The reason for replacing it was - my 440 would get a bit on the hotter side sitting in the traffic on a 96 degree day. The temp would get up to 195 - 200* but will drop as soon as I start driving. So I installed this HD clutch and a 160 thermostat (I had 180 previously) and there is no change.. Still gets up to 195 in traffic.
The weird thing is now even if I am cruising at 40 mph (1800 RPM) the temp would slowly increase and get up to 195* on a hot day, or up to 185* on a 76* day (that`s with 160 thermostat). By saying slowly I mean 20 min period.
I understand that the fan should not come into play at cruising speeds, therefore I will be checking the t-stat, but still curious about fan clutch operation.
PS. I noticed that every time I shut the engine off I hear air bubbles moving - does that mean I have to bleed the system again?
 
The automatic fan clutch has two modes of operation, the engaged mode and the disengaged mode. The disengaged mode ( engine cold or high speed driving conditions ) occurs when the silicone fluid is contained in the reservoir area of the fan clutch. As the temperature of the engine rises so does the temperature of the bimetallic coil. This bimetallic coil is connected to the arm shaft in such a way that as the temperature rises the shaft moves the arm exposing an opening in the pump plate. This opening allows the silicone fluid to flow from the reservoir into the working chamber of the automatic fan clutch.

The silicone fluid is kept circulating through the fan clutch by wipers located on the pump plate. A hole is located in front of each wiper, the speed differential between the clutch plate and the pump plate develops high pressure areas in front of the wipers, thus the fluid is forced back into the reservoir. But as the temperature rises the arm uncovers more of the large opening and allows more silicone fluid to re-enter the working chamber.

The automatic fan clutch becomes fully engaged when the silicone fluid, circulating between the working chamber and the reservoir, reaches a sufficient level in the working chamber to completely fill the grooves in the clutch body and the clutch plate. The resistance of the silicone fluid to the shearing action caused by the speed differential between the grooves transmits torque to the clutch body. The reverse situation occurs when the temperature drops. The arm slowly closes off the return hole thus blocking the fluid flow from the reservoir into the working chamber.

The continuous action of the wipers removes the silicone fluid from the grooves in the working chamber and reduces the shearing action. Less torque is transmitted to the clutch body and the speed of the fan decreases. The temperature at which the automatic fan clutch engages and disengages is controlled by the setting of the bimetallic coil. This setting is tailored to satisfy the cooling requirements of each make and model.
 
as far as the speed of the engine goes, the faster you drive the fluid drains away from the the working chamber thus allowing the fan to free wheel when it is not required while driving at highway speeds.
Once you are at or a near idle state the clutch starts the process of filling the working chamber again. causing the fan to engage.

The biggest failure point is that the fluid leaks out and the reservoir goes empty so the clutch can't engage

My 2008 F150 in colder weather will engage the clutch because the silicone fluid is thicker at first until it warms up to be able to free wheel until the engine needs cooling.
 
Last edited:
id go back to a 180 tstat IMO also. if its tooo cool a tstat, the water does not sit long enough in the rad to cool down any.

try not to die -

- saylor
 
superfragl said:
Hi folks,
I am not sure if I am getting it right. As I understand, a thermal clutch (the one with the spring) is supposed to lock or at least the friction should increase as the radiator temperatures increase. I purchased new HD clutch (from Autozone) and tested it with a heat gun. I heated it up to 180* but it only got looser. Is this normal??
The reason for replacing it was - my 440 would get a bit on the hotter side sitting in the traffic on a 96 degree day. The temp would get up to 195 - 200* but will drop as soon as I start driving. So I installed this HD clutch and a 160 thermostat (I had 180 previously) and there is no change.. Still gets up to 195 in traffic.
The weird thing is now even if I am cruising at 40 mph (1800 RPM) the temp would slowly increase and get up to 195* on a hot day, or up to 185* on a 76* day (that`s with 160 thermostat). By saying slowly I mean 20 min period.
I understand that the fan should not come into play at cruising speeds, therefore I will be checking the t-stat, but still curious about fan clutch operation.
PS. I noticed that every time I shut the engine off I hear air bubbles moving - does that mean I have to bleed the system again?
Click to expand...
It's my opinion that those temps are not that bad. If it was shooting to 225+ I'd be concerned.
 
saylor said:
id go back to a 180 tstat IMO also. if its tooo cool a tstat, the water does not sit long enough in the rad to cool down any.

try not to die -

- saylor
Click to expand...
X2. If the T Stat is too low a temp, it may remain open to long and not cycle correctly.

Never knew that about the clutch fan, just thought it disengaged at highway speed to save on unnecessary engine drag.

Superfragl, are you also using an overflow bottle and fan shroud? These should help your temp problem as well.
 
No overflow bottle, but I do have a shroud. 26" aluminum radiator (two rows of 1" tubes). The clutch is about 1" away from radiator. I thought maybe the engine is running lean and therefore gets hot - pulled a plug and look nice - light tan color.

Snotty said:
It's my opinion that those temps are not that bad. If it was shooting to 225+ I'd be concerned.
Click to expand...
I agree - not bad, I have never seen temps higher than 200. My concern was that temps are higher than t-stat rating.
 
superfragl said:
No overflow bottle, but I do have a shroud. 26" aluminum radiator (two rows of 1" tubes). The clutch is about 1" away from radiator. I thought maybe the engine is running lean and therefore gets hot - pulled a plug and look nice - light tan color.


I agree - not bad, I have never seen temps higher than 200. My concern was that temps are higher than t-stat rating.
Click to expand...
T-state rating only tells you when it will be fully open, not the ultimate running temp. That will be the same whether it's a 160 or 180.
 
The only thing I still don`t get is when the bimetallic spring kicks in and how to test it? So far - heating it up to 180 degrees made the clutch looser, But I am not sure if the clutch is supposed to be spinning in order to operate properly...
 
superfragl said:
The only thing I still don`t get is when the bimetallic spring kicks in and how to test it? So far - heating it up to 180 degrees made the clutch looser, But I am not sure if the clutch is supposed to be spinning in order to operate properly...
Click to expand...

The clutch fan should be free wheeling regardless on the temperature until it starts to hit about 210'ish then it will "lock up" or get stiffer to turn by hand but they will always be able to be spun by hand..
I've seen some in the past that totally locked up which required replacement

Here are a few videos on how the Mopar style works too.



Some people try to refill them but usually there is a reason why it is out of fluid.. it has a leak! means the seals are pooched.

sometimes the spring rusts up so it can't open or close the valve. you can sometimes free it up with a penetrating fluid.

In most cases and for the price it is time to replace with B/N
 
superfragl said:
Hi folks,
The reason for replacing it was - my 440 would get a bit on the hotter side sitting in the traffic on a 96 degree day. The temp would get up to 195 - 200* but will drop as soon as I start driving. So I installed this HD clutch and a 160 thermostat (I had 180 previously) and there is no change.. Still gets up to 195 in traffic.
The weird thing is now even if I am cruising at 40 mph (1800 RPM) the temp would slowly increase and get up to 195* on a hot day, or up to 185* on a 76* day (that`s with 160 thermostat). By saying slowly I mean 20 min period.
Click to expand...

Go back to a 180 or 195 F thermostat. Mopar dropped the 160 circa 1965 in favor of the 180 to get more fuel to burn in the cylinder. Be glad your motor runs at the same temp as mine, around 195-200 on a very hot day. This way, you're burning just about every hydrocarbon you're supposed to burn on the power cycle. Clean emissions, efficient running all result. You can get a higher pressure cap, keep your coolant at the prescribed 50% ethylene glycol level and your coolant won't boil until it reaches well over 212 F. I think 250 F is the boiling point w a 16 psi system, if you're worried.
 
I actually just uninstalled my clutch fan, Pretty sure it stopped working as it was intended to years ago. I just installed a somewhat cheap fixed fan that appears to blow way more air anyway. And It's plymouth blue.

Anyhow the Clutch fan seems to be more of a headache than anything else. That's just my experience anyway. Also taking the fan off to replace the water pump can get a little tricky.
 
TheFearlessFury said:
Also taking the fan off to replace the water pump can get a little tricky.
Click to expand...
Putting it back on is easier if you stick a wire tie through the pump, pulley, spacer (if needed) and clutch before you start bolting things together.

 
Big_John said:
Putting it back on is easier if you stick a wire tie through the pump, pulley, spacer (if needed) and clutch before you start bolting things together.

Click to expand...
I can see that, Good thing I only needed to take it off once lol
 
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