Best way to test engine fan clutch
 

Hello! Since I've never heard the engine fan spool up, even with the coolant going up to 100°, I think that my fan clutch's dead. However, on spinning the fan clutch with the engine shut down, it feels like there's resistance, so I'm not sure that it is in fact dead.

Is there a sure-fire way to test the clutch? Also, how loud is the fan on these cars when it is engaged? The fan on my truck will drown out the engine when it's spinning at speed, and I've always assumed that it would be the same on the car...

Thanks in advance!

Best test is to get the engine up to the temp where you know it should be on (idle on a hot day until the aux fan comes one without the AC running), then shut off the engine while watching the fan (easier with a helper).

The fan blades must stop within one revolution. Any more and the clutch is shot. I have a spare for the 300TE, since the temp goes up to 100 or so in traffic -- but haven't managed to get it on yet. Probably will do it in a week or two, also the belt since it's been on there for three years at least now.

There should be enough increase in air volume to notice, but I don't know how much. I guess I could test the 300D sometime. However, the Volvo shoulds like a jet engine, no mistaking THAT for anything else!

Peter

My truck's the exact same way, as was my old van. Very cool sound IMHO :D

What temp is the clutch supposed to engage at? Should the engine be at the temperatue that the fan's supposed to engage at, or at "standard" operating temperature? I don't know if it makes a difference regarding the test, but my aux fan doesn't work either...yet.

I'll give the test a try...thanks!

Warden,

I think I read in a MB manual that you should compare a suspected bad viscous clutch to a good one.

P E H

Fan usually engages at an engine temp of less than 100C, maybe 95C. The aux fan should kick in at 100C.

Certainly, you should hear it roar when it engages, louder at speed than at idle, but the airflow must increase substantailly.

I suspect the visco clutch is bad on the 280 SE -- not a good thing, as a new one is $300 plus these days...

Peter

Peter

visco clutch
 

I asked the same question at the local MB works 2 weeks ago. The old mechanic's reply was as follows : when the engine temp is over 90 (even better over 100), when you put your hand between the fan and the engine and rev up (watch your hand), you must feel a 'solid' draft of air. He said they didn't test the clutch in any other manner, only replaced them.

The Warden,

According to the manual on CD for the W124 series if you have a viscous clutch, it engages when the air temperature coming over the hub after it goes through the radiator reaches about 70*C. The clutch is activated by a bi-metallic spring that changes shape and lets the viscous clutch fluid out of a reservoir. The manual suggests this happens at a water temperature of approximately 100*C, or should.

The recommended test is to listen with the engine running at a higher speed, like 2500 to 3000 rpm. The fan makes a load of noise at that speed. Also, at higher rpm the fan does not increase speed directly with engine speed, and that is supposed to be apparent too. Part of the clutch design is to limit the torque it transmits to the fan, and so, below some maximum rpm, near 3000, the fan speed is directly related to the engine speed, while above that the torque demand to increase speed exceeds the clutch capability. As the engine revs higher the clutch slips and the fan reaches a maximum speed.

The electo-magnetic clutch units are easier to test. A switch senses coolant temperature and changes state, triggering the clutch to close. This can be tested at the switch and at the clutch.

By the way the engine cross section of the 240D engine (in the engine manual) does not show any kind of clutch. It seems like it is a solid connection from the four bolts to the water pump shaft hub, while a 300D TurboDiesel seems to have a viscous clutch in my manuals. No mention of them though in the text. If it has no clutch, then there is another thing in favor of the simpler is more reliable discussion that favors the 240D over a 300D TurboDiesel.

Of the two clutch concepts, I wonder which one is the more reliable? Good luck, Jim

I suspect the visco clutch is better as it will always give some air motion, even if bad. The electric clutch lets the fan freewheel if it fails, unless it locks up.

The W115 220D and 240D don't have a clutch, don't know about the W123.

Peter