W126 viscus fan, how to test?
 

I have a new sound now that its rather cold out. I suspect my viscus fan is bad. I am not sure if its adjustable, if it is then maybe an adjustment could help.

When I start the car, its near impossible to hold the fan. Even in temps around 40 degrees, it wants to go. Yet when I turn the car off (when warmed up) the fan will spin down for about 10 seconds. Cold or warm, I can move it by hand fairly easily. If I try to spin it, I get maybe a half rotation. It feels smooth when moving, but there is slight play when rocked front to back by hand.

With the cold weather I have a new sound. Which I think is the fan. When the car is started cold there is a sound like something is hitting the fan blades. Suck as a small stick or something. I have checked it many times and there is no visible contact. When I turn off the car I also hear this sound a couple times as the fan spins down. But this is all only when its cold, I don't notice it when warm.

Anyway, sorry for the novel. Any tips would be nice. But I suspect replacement will be required.

If you suspect the fan, perhaps your engine mounts have collapsed, letting the fan hit the shroud under certain conditions.

Re testing the fan: With the engine warmed up, rev the engine up past 1500-1800 rpm, and as the engine revs up, listen for the fan to couple. You should hear an increase in fan noise.

Jim

There shouldn't be any fore and aft play in a viscous fan clutch. It might be that the bearing in it is worn.
I've just fitted a new viscous clutch to a W124 'just in case' it cures an idle overheating issue: the new clutch is much stiffer than the old one, although that seemed reasonable after 200k miles.

New mounts. And I did check for hitting many times :( And I can only observe the sound at idle anyway so I doubt the mounts - which are only about a half-year old or so. And when I rev the engine the noise goes away. Its seems to be a cold/idle issue.

Mine is shot and it spins all the time. Also free spinning by hand both directions. No fore/aft play though. Maybe the noise is internal to the clutch?

I have two 15+ yr. old vehicles with viscous fan clutches - one in my sig.

My experience has been they're working when they lock up at shutdown when the engine is good and hot. It gets HOT where I live from late April to early Oct. Lots of opportunities to test a VC.

I believe the OP is in Wisconsin.

If I'm right - it will be a long time B4 a WI car equipped with a VC can be tested.

With winter here - I'm not too sure I'd worry about it that much.

You could hold the engine at 3000 RPM, eventually it will get hot enough to lock the clutch and you'll hear the fan speed up.

-J

Thats what I am thinking now.

I have a viscous fan clutch on my 280CE (W123). I'm pretty sure it's seized. You can turn it by hand when the engine's off but it's very stiff (stops moving as soon as you stop moving it, so doesn't rotate at all on its own).

Tried starting it cold then shutting down and it stops dead with the engine.

Makes a lot of noise when driving - as it's moving at engine speed. I'm thinking of just using an electric fan instead. I know an electric fan isn't original, but others seem to have had success - quieter running etc. And it'd be cheaper than a new viscous clutch.

Mike

I wonder if my electrics will kick in if the engine gets hot enough. Unless they are for AC only. But I could maybe wire in a circuit for them. I would rather run electric if I can. But I do love the sound of a viscus fan!

The electrics kick in at like 110*C

-J

If it has factory a/c, the electric cooling fans are probably pressure switched from the a/c system rather than by engine temperature.

The fans have 2 speeds. Low speed is kicked on by the AC pressure, high speed by coolant temp.

I have alot of slop in the shaft, I can wiggle the fan around and up and down, can the bearing itself be replaced? or do I HAVE TO buy a new clutch?

If I hold the pulley the fan clutch has some tension, it's not freewheeling or locked...but I do have a bad bearing I'm convinced.

In my experience, the fhe fan clutch should be pretty tight when stone cold, and immediately begin to loosen up when cranked. It should not make too much noise even when revved up 30 seconds or so after a cold start. When warm or hot, it should move quite freely, spin at least one full turn when spun by hand. Here in Texas I've never seen mine tighten up when turning off a hot engine and letting it heat soak. The ONLY time I hear it tighten up when driving is when the AC is NOT on and the engine sits at a red light for awhile, taking the temp above 100 but not to 110. Then it will rev audibly for a few seconds when starting off. When the AC is on, the low electric fan comes on via a pressure switch and keeps the temp lower, and stops the clutch fan from tightening up. With AC off the low fan is off always, so the motor heats up more standing still. Then the hi fan comes on at 110, this will declutch the clutch fan in a few seconds.
my fan has always had a little play in the clutch - still going after 20 years though.

The cold noise could be the smog pump; they only run for about 5 minutes after a cold start, and they make that exact noise. Easy to check, you can trace the wire back to the fender and unplug it for awhile. But the noise during shutdown couldn't be that. The shroud was a good guess, also maybe the little belt tensioner shock. Also, when the motor mounts sag a bit, the little motor shock absorbers next to the mounts will bottom out and click as the engine rocks. I had this for nearly a year before I found it.

Good luck,
DG