Should my engine fan be "roaring" on acceleration?
 

I know that with the clutch fan, that a "roaring" sound is normal, but I do not think mine is working enough. I am wondering - when I first leave in my car and get on the mail road and accelerate, the fan will roar, like it is really pulling in air, but then when I get to about 40 MPH, it slows down. I NEVER hear it again throughout the day, even when the engine temperature surpasses 100*C. Shouldn't I be hearing this fan more often, especially when the engine temperature goes past 100*C? BTW - my car is a 1985 W126. Since it is working initially, does that mean it is OK? I am just wondering, because I have had cars in the past that roars most all of the time.

Thanks.

VernDammit fan clutch!
 

See Above

The fan clutch is supposed engage when hot and dissengage when cooled.

Stop your car when good and warm, with the engine off reach in and see if you can easily spin the fan. If so, I suspect the fan clutch.

Haasman

checking fan clutch
 

i learned this from a friend who has an engine building shop. the first time you do it it's a bit nervewracking. firmly hold a fanblade in each hand and have an assistant start the engine. at cold idle you should feel 5-10 pounds of inertial force attempting to spin the fan if the fan clutch is good. if it has failed you will feel little or no resistance and will be able to spin the fan backwards. have assistant stop the engine before releasing fan. i can't wait to see the replies on this.

it's happened to me before.... fan clutch.

Makes sense, just don't let it get away from you!:eek:

I'd rather be the one starting the car!:D

Yea, me too. How dear to you is your wife?

yikes!.... this is one i would only want to watch someone else try.

tom w

Thanks for the replies. I will check that soon, but I do not think that *I* will be holding that fan blade. :D I will probably let the shop check it.

I am battling another problem now with the car stalling out. :mad:

How many fingers does this guy have? And what does he do if the clutch has failed in a locked position and the fan spins with the starter cranking and then spins up to a nice full speed when idling?

you can reach in stop the plastic fans with the engine running at idle. I can't remember why I tried it the first time but I have done it a bunch of times since then and only have 8 fingers left to go.

Depends on the state of the clutch fan and type. If it is a viscous clutch fan that the clutch engages as heat rises then yes a normal operating one is able to be stopped by hand. And most fail in the free wheeling state. But what if is fails and locks on full? Then you be losing a finger or two. What if the engine has a locking magnetic clutch on it? That baby fails locked on and you will be missing some parts later. It is not a bright idea to grab a fan of any kind when the engine is running. And I have never actually witnessed a tech dumb enough to grab a moving fan. I am sure they do but it is not the most inteligent thing to do.

Viscuous drive clutch fans will spin at close to the speed of the pulley when the fan is cool (engine hasn't run for a while) at idle. I believe this is due to the media (some silicone like compound) being cool and there is some settling of the media if the vehicle sits even overnight. When they warm up and say you are driving at 60mph and if working properly the fan will basically freewheel as a function of the air velocity coming through the radiator. If the air were blocked from coming through the radiator (while at 60mph) the fan will spin slower than the idle speed of the pulley (with engine disengaged from driveshaft).
Thermal clutch fans are much superior to straight viscuous drive, so if your's go bad I think it well worth it to get a thermal clutch fan, their rpm is a function of the temp of the radiator right in front of the fan, rather than mostly just lagging engine speed.

the fan on my mercedes would take a hand off, i stuck a screw driver in it once and it did not stop the thing and then when i got in an accident the fan chewed up the radiator..:mad:

The 107 manual claims that it operates at approximately 1/2 speed. I've been toying with buying or making an infrared RPM meter to verify this.

With all the trouble (and expense) these clutches cause, you wonder why no one has made a hub for a flex fan blade to bolt on to (well, it's definitely going to be noisier, and chopping a finger off if you stick it in the moving blade is just about guaranteed). Maybe liability?