I always though the way a fan clutch works (thermo-controlled) is when it senses a predetermined temp it locks up when the engine reaches the lower rpms and disengages when the engine speed increases as to keep a certain amount of air flow at all times.

My fan clutch will lock up and stay locked up at all rpms when it detects a certain temp.....usually a little while after I've started driving it.

It's a fairly new part too....this isn't suppose to work like this is it?

I always thought they stayed locked until the temp went below the predetermined setting. JMO

If I am not mistaken I think that with heat the clutch gets tighter as temp decreases it loosens up.

The purpose of the viscous fan is to allow the temperature to regulate the speed needed to cool the radiator down. Some mechanics ?? will force the fan by using a broom handle against the fan pully...Lots of stupids.By the way-there are fiberglass fan blades that can break off and cause death. Never stand in front of the direction of the rotating.

I believe in a fan clutch setup. For a performance application I use viscous fan clutches only. In a truck or trailering application I prefer a thermostatic fan clutch. Here's why: in a performance application higher rpms means speed and acceleration, and the cars road speed remains low for just a brief moment. In a trailering application you can have a vehicle in a low gear going up a grade with little road speed, but high rpms. In a trailering application there may not be enough road speed airflow through the radiator for best cooling - so you want the fan to remain engaged and pulling air through the radiator if the underhood temperature is high.

Many thermostatic fan clutches will remain locked when cold for a couple of miles, then they usually disengage unless they are really still needed. If your thermo-clutch remains locked no matter how long you drive it then either: a) your underhood temperatures are excessive (as in you have a cooling problem), or b) the thermo-clutch is defective.

Thomas

Stay away from fiberglass fans. WHATEVER YOU DO DONT USE THEM. I had one break and go through my radiator shroud. I was very lucky. It didn't hit me or take out the hood.

First off what are these vicious clutches you speak of? I've never heard of such a thing.

The clutch for my fan is disengaged when I start the engine. It spins freely at this point. It's not until after I've driven the car for some time that the clutch locks up and stays locked up. I don't believe it ever unlocks until the temp goes down a little.

It remains locked up at all engine speeds...evident by the whooshing sound it causes the fan to make in the higher rpms. My engine sees anywhere from 2000-6000 rpms.

According to my water temp gauge it never goes above 195, though most of the time it stays at 180. I do have a set of uncoated headers on the engine.

So should I stay with this thermo style clutch? Or go with another type? This is a performance engine.

:) Anyone know?

Perhaps my clutch is not working right???????

The two types in question are thermostatic and centrifugal fan clutches. Thermostatic are temperature engaged and disengaged. Centrifugals are speed dependant.

Which would be good for an engine that sees 2000-4000 on an average road trip? Yeah I have some pretty low gears and a semi-high stall converter.

A thermostatic fan clutch usually always has some kind of bi-metal spring (the thermostat) on the front face of the clutch. A viscous clutch centrifugally disengages - usually always limiting the fan speed to less than 4,000 rpm even when the engine speed is well beyond that.

A bad thermostat on a thermostatic fan clutch will keep the fan engaged even when the underhood temperature remains low. If the "whooshing" sound never ends, then the clutch is locked.

Many years ago (~25?) I learned to respect the space directly to the sides of an engine fan - a local kid was killed when a fiberglass blade broke loose as his brother was revving the engine. I might be wrong, but after that I decided that the non-fan clutch fixed plastic/fiberglass "flex" fan blades were a ticking time bomb.

On the highway you have no need for a fan - the road speed alone gives all the radiator airflow needed. Low road speed operation is a different story.

Thomas

That's what I'm thinking....when moving down the road there's more air being forced thru the radiator so there's no need for the fan to be locked up...plus it just robs power from the engine for acceleration.

However when stopped now there's no air moving thru the radiator so now the fan should lock up as to start bringing in more air and not cause the engine to overheat.

The above mentioned were my understanding on how fan clutches performed.

Fortunatley my fan is a metal fan I got from a late 70's Malibu.

Would the viscous clutch be better for a high performance application?

i recently saw a shoot out where the stock clutch fans far outperformed most all aftermarket varieties, cooling and hp loss, you should also know that a clutch fan is still apt to turn even when when not engaged, at idle and/or at road speed

For the non BELIEVERS All Big Block--70s FORD-GM--Mopar YES ALL High horse big cube engines had clutch fans. WHY To start with a 16-22 HP. gain over a fixed fan. They barely see 3000 grand. Look real good at a 70 BB. Fan shroud. The left side is open for highway cooling, While the clutch fan is floating around from the air being forced in the rad. at 50-60 MPH. A Chevelle must for proper cooling.!!! ALL the rubber items under the hood that Chevrolet put in place MUST be there. WHY? The cooling design for a 70 BB--Ambent air enters through the grill and is forced to exit near the Left rear and the right rear exhaust manifolds. This is the designed exit, If you interfear with this airflow design in any way, Such as removing so called splash guards, Any factory rubber products. YOU will create swirling and underhood turblance. This will cause air NOT to flow through the rad--increasing water temp.--increasing engine temp.--increasing underhood temp--Boiling of fuel AKA vapor lock. How do I know this? I had a major issue with temperature And my brother a retired Ford guy hooked me up with a Chevy Guy a retired Thermo. Eng. from Detroit. R&D man for Chevy. If you say this is B.S. I have a question Why are part numbers stamped on fan blades, such as 3947772.? This is to long, time to go. Bob ACES 2825

Quoted fron the Hayden website FAQ section:
"Most fan clutches are designed to engage around 170 deg air temperature (180/190 deg engine coolant temp) and disengage after the temp drops 20 deg. When engaged, a Standard Duty fan clutch will spin about 75% of shaft speed and a Heavy Duty fan clutch will spin about 90% of shaft speed. When disengaged it will spin about 33% of shaft speed."

Yep I know the fan will always spin as long as the engine is going, just it spins sometimes faster than others.