Should i put an clutch fan on?

[Bman]

Okay so my truck currently has a direct drive fan, no clutch

And i found a clutch fan today digging around in my dads barn. seems to be in good working order.

Should i put in on my truck?

Is there really any advantages to having a clutch fan?

 

[firebane]

Yes put it on. Truck will be happier and run better.

 

[chengny]

A fan clutch serves two purposes:

1. An increase in engine efficiency - which results in a slight increase in fuel economy.

2. More stable control of engine coolant temperature

The design of the viscous coupling in the clutch is such that it will only drive the fan when required. If the air flow out of the radiator is cool, the clutch allows some "slip" and the fan blades are not driven at the same speed as the drive flange. As the temperature of the air leaving the radiator increases, the clutch "tightens up" and begins to drive the blades at a speed closer to the speed of the drive flange.

An increase in economy is achieved simply by not having to drive the fan at full speed under all conditions.

Another advantage is; because the fan speed is reduced when not required, there is less of a temperature drop of the coolant across the radiator. So - on a cold day - instead of ice cold coolant entering the engine, the coolant is at a more moderate temperature. This helps the thermostat more easily maintain the engine's design operating conditions and prevents large swings in temperature as well as reducing thermal stress.


One thing about this type fan clutch that should be mentioned - they should always be stored in an upright position (i.e. just as they would be if installed on the engine). If allowed to lay on their sides for any length of time, it is possible that some of the silicone charge can be lost. After that they will no longer function as designed. In the worst case, instead of allowing the fan blades to slip as the temperature rises, they will remain hard coupled and always drive the blades at full speed.

 

[firebane]

Let me be the first to say... I HAD a fixed fan and could not get my truck to proper operating temperatures. I now have to switch out to a clutch fan.

 

[MadOgre]

That is the same reason why my vintage fan sits on top of my tool box and not on the front of my engine

 

[bucket]

I like the factory flex fans from the 70's because they are quiet and there's not much to fail... so long as there's no cracked blades.

One thing about this type fan clutch that should be mentioned - they should always be stored in an upright position (i.e. just as they would be if installed on the engine). If allowed to lay on their sides for any length of time, it is possible that some of the silicone charge can be lost. After that they will no longer function as designed. In the worst case, instead of allowing the fan blades to slip as the temperature rises, they will remain hard coupled and always drive the blades at full speed.

This would explain my complaint with a lot of parts store fan clutches. They are stored in a box laying flat and make all sorts of windy noises when you drive after the install.

 

[chengny]

A few years ago, I had a lot of trouble getting my head around how these fan clutches work. Somebody gave me this:


Thermal Fan Clutch

Varies the fan speed with temperature of the air behind the radiator.

Engaged (high speed) operation provides maximum cooling.

Disengaged (low speed) operation provides fuel savings and noise reduction.

Greater life expectancy than a non-thermal clutch.

Briefly engaged at cold start-up.

Engages at about 170° radiator air temperature, (about 30° lower than coolant temperature).


The air temperature coming through the radiator is sensed by the bi-metal thermal spring on the front of the thermal fan clutch. It expands and contracts with the change in air temperature operating a valve inside of the clutch. When cold, the silicone drive fluid is pumped from the working area to the reservoir. When hot, the valve opens allowing fluid from the reservoir to be transferred to the working area thereby increasing the fan speed. The clutch disengages as the air temperature decreases, closing the valve and allowing the silicone fluid to be pumped back into the reservoir.

A thermal fan clutch is engaged on a cold startup because the fluid drains into the working area when the engine is shut off. The fan clutch will slow down shortly after startup as a result of a pumping action produced by a difference in speed between the shaft and the body of the clutch.

Most models are designed to duplicate original equipment performance. Some Chevrolet/GMC truck models are specifically designed to engage at lower temperatures than the original equipment parts that they replace.

You must be registered for see images attach

 

[Bman]

It was laying face down till I found it. How do I know if its okay? And so it allows slip when cool/ at running temp, but if it warms it will lock up more and spin faster?

 

[chengny]

Best tested under actual operating conditions. I have a couple of tricks to bench test - but I wouldn't feel comfortable suggesting that someone else use them. Best to install the clutch and use this procedure to verify proper operation. NOTE - the last test is very dangerous. If you do it, for God Sake's be frickin' careful!:


Testing a fan clutch

If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch:

1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good
indication. If it does not increase speed/noise, clutch is bad and needs to be replaced.
(Remember, this must be tested after the car has been off for and extended period, over
night etc.)

If it passed the first test continue as below.

2. Leave engine running and note if the fan starts to slow down after 2-5 minutes. Speed/noise should diminish. Even while raising the RPM, the fan should not make as much noise as when first starting. If it does slow, this is the second good indication. If
speed/noise does not decrease, clutch may be “frozen” and should be replaced.


3. Leave the engine idle and watch the temperature indicator. When normal operating
temperature has been reached, some increase in fan speed/noise should be noted, in
particular when the RPM is increased. If temperature is fairly stable and the fan
noise/speed increases or cycles, third good indication. If temperature indication continues
to increase, with no increase in fan noise/speed, clutch is defective and should be
replaced.


4. After the engine is at normal operating temperature or above, is the only time that the
“rolled up newspaper” test that many people talk about should be performed!

Take some newspaper and roll it up into a long narrow tube. Be careful, keep hands and fingers away from the fan while performing this test!

With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub.

Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.

Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.


Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”.

 

[DoubleDingo]

I knew a guy in high school, a real moron at best, the way he tested fan clutches was with a rag in his hand, and then he grabbed the fan while the engine was running. Do not do that.

 

[Bman]

Well ive run into an issue. The fan i have is built for short bolts and nuts, my straight blade fan is put on with long bolts only.

any ideas on how to convert this setup?

 

[MadOgre]

You mean studs ? One end is fine thread the other regular threads ?

 

[MadOgre]

Just get some bolts long enough or short enough that have the proper threads and bolt it to the water pump.

Your local fastener shop will be able to set you up or maybe even your hardware store.

They should be fine threads the bolts that you get to bolt into the water pump.

 

[MadOgre]

Spacers could work too

 

[MikeB]

Thought I'd share the info below from Hayden. As you can see, a fan clutch never totally engages or disengages. Also, the fan pitch must be matched to the fan clutch. I suspect using a large pitch fan on a standard clutch would overheat the clutch.

Standard Duty Thermal
Turns fan 60-70% of shaft speed when engaged
Disengage to 20-30% of the shaft speed
Used with lighter pitch fans. (1-1/2” of pitch)
Flat plate impeller design with up to 11.4 Sq. In. of working surface
Identified by a smooth steel faceplate & thermal spring assembly on the front side

Heavy-Duty Thermal
Turns the fan 70-90% of the shaft speed when engaged for increased cooling
Turns the fan 25-35% of the shaft speed when disengaged
Used with deeper pitch fans. (2-1/2” of pitch)
Land and groove design with up to 27 Sq. In. of working surface
Identified by finned aluminum faceplate and thermal spring on the front

Severe Duty Thermal
Turns the fan 80-90% of the shaft speed when engaged
Turns the fan 20-30% of the shaft speed when disengaged
Used with deeper pitch fans. (2-1/2” of pitch)
Land and groove design with up to 72 Sq. In. of working area
Larger working surface provides cooler running and longer life expectancy
Thicker body and deep finned faceplate dissipate more heat
Can be used in place of many heavy-duty clutches

Then there's this style, which I see no reason for using:

Non-Thermal Fan Clutch
Low cost alternative for some standard thermal clutches.
Always engaged, less fuel savings than a thermal clutch.
Spins at about 30-60% of the water pump speed.
Shorter life expectancy.
Cannot replace a heavy-duty clutch.
Identified by the smooth, steel faceplate, (without a thermal spring assembly), on the front.