I installed a new BEHR fan clutch in my 87 300D last April. Since that time I have questioned weather or not it was working properly. Today I watched the fan for the time it would to stop turning upon shutting off the engine. It spun freely for about 15 seconds before it came to a stop. If I give it a spin by hand, it spins with no resistance, even while the engine is fully up to temp.

Does this sound like a bad fan clutch?

How common is it to get a bad replacement fan clutch?

I ordered a new fan clutch from the supplier I bought the first fan clutch from with the understanding that they would credit me for the defective fan clutch, if it is defective?

Anybody got some input?

Is it a Behr thermo clutch?
The thing should never spin without some resistance, especially hot as the resistance should increase with temperature.
It sounds like the fluid has been lost. Is there a lot of dust sticking to some arease where fluid would acumulate around the center of the clutch?
I had a new clutch on a 123 chassis fail within a year of purchase.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

BB, the fan clutch won't couple until the air temperature at the sensing coil is at 100°C. or above. At normal temps, the fan never does anything.

It seems like an expensive gadget for 99% of all the time that the engine operates.

You would need to let it idle with the a/c on, on a very hot day, and, hopefully, the temp. will climb up to 100°C. Then shut it off and see if the fan has coupled.

I don't believe I've ever felt any resistance from my fan clutch, and the engine almost never reaches, let alone exceeds 100C. Just monitor your temps and make sure your aux. fan works correctly as a back up. Life's too short to worry.

Supposedly you're supposed to store the clutch such that the spin axis is horizontal. The manual says to keep the axis horizontal even when the clutch is off the car to change a belt. Maybe your clutch spent time with the axis vertical.

Sixto
95 S420
87 300SDL

Thank's guys, this is all pretty interesting! Hard to tell how the supplier stores his clutch fans. Now that I have the engine cooled down, not run in 3 hours, the clutch fan has resistance. But when hot, it has no resistance!

With the A/C on, at idle, I'll try to get it up to 105c, or when the aux fan comes on and then see if the fan clutch builds resistance so it can turn the fan. If so, I'll cancel my new replacement order!

Today I installed the new replacement BEHR fan clutch. No difference in function between the last April's new replacement BEHR fan clutch and this one.

Either I have received yet another defective fan clutch, or temperatures are not getting high enough to engage. Brian Carlton says over 100c and it should begin to engage, or be engaged.

With the A/C on, in drive, I've been able to get it hot enough in order for the aux fan to kick in, 105c, then disconnected the power supply to the aux fan in order to raise the temp even higher, still no action from the fan clutch. In fact, at this elevated temperature, engine running, I can actually stop the fan and clutch with my fingers and hold the fan still.

What is wrong here?

I've spent now $345 for two seemingly defective fan clutches! I'd love for someone to tell me there is for sure something wrong with both fan clutches, but I'm not fully sure!

One possiblility is that nothing is wrong... Perhaps the M-B design is to very loosely couple the fan.

My SDL fan seems quite lazy, and it too freewheels when the engine is shut off, but it does spin. A spinning fan will pull air thru the condensor and radiator.

I have found that without A/C, not much airflow is needed. At highway speeds, I bet the fan could be thrown away, and in stop/go the engine-mounted fan is supplemented at 105C by the auxiliary fan.

With A/C, the aux fan is pretty much a mandatory item except at speeds over 30-40mph.

Best Regards,
Jim

This is quite interesting.

My only thoughts are as follows:

The fan clutch will couple when the temp of the thermostatic spring in the clutch reaches about 100°C.

So, with the vehicle's temperature gauge at 105°C, you would think that the temp in proximity to the spring would be nearly 100°C. and the clutch would couple.

I'll get Dave to comment on the clutch. He's had them definitely working in the past. I'm fairly sure mine does not work, but, I'm not worried about it.

Over the years and many cars, it was quite often during the summer months to hear the fan start to pull air, especially in stop and go traffic on a hot sunny day.

Both of these new fan clutches have a bit of resistance to them when cold, but become easy to turn, after shutting off the warmed up engine. You'd think it would be the other way around!

Wonder what Doctor Bert, or GSXR, might have to add to this saga?

Exactly, all clutched fans I've had are locked when cold then unlock when warm up to near operating temps...

That's why I believe neither work on my cars.

Makes sense as the oil in there thins out as temps increase (it's too thick when cold) and relies on that piece of metal at a certain temp to lock it up... at least how I view it.

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1) The OM603 FSM has data on how the original clutch should engage... usually when coolant temp is above approx 90-95C. HOWEVER, the replacement clutch (with plastic fan) is from an OM606 and the FSM is silent on engagement temp. I believe it is a higher temp, in search of better MPG and emissions. On my cars, it may not lock up until the dash gauge is in the 100-105C range (or maybe higher).

2) Remember that the clutch is triggered by the temp of the AIR FLOW directly on the face of the clutch. If that area of the radiator (or condenser) has airflow blocked, or if the radiator has a 'cool spot' right there, even a perfect fan clutch WILL NEVER ENGAGE. Many a clutch has been replaced when the real problem was either a bad radiator (not uncommon on the 603 for some reason) or dirty rad/condesner fins.

3) From what is described, I'd bet a 3.5L con rod ( ) that the new clutches are working perfectly, but that it is never 'seeing' hot enough air to engage the clutch. When it's locked and you shut off the motor, the fan stops immediately or within approx 1 revolution, at least both my cars did this when locked. I usually needed the ambient temps to be 95-100F and the dash gauge to be at 100-105C to get it to lock.

4) The vertical storage thing is, IMO, a crock of stuff. New ones are shipped in any direction. I believe this only applies to used clutches.

5) Anyone who thinks the fan doesn't do squat at freeway speeds should remove the fan in the summer and go for a drive at 55-75mph and report back. You may be surprised at the results. (Tip: Bring the fan with you, and the special tools, so you can re-install it on the side of the road.)

6) If the fins are all clean and airflow is normal, I'll almost guarantee the radiator is the problem. An IR thermometer is helpful here, or you can try to feel (carefully!) if the area in front of the fan is blazing hot like it should be with the engine at 100°C+.

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It seems that MB have gone out of their way to run the 603 hot. I suspect that the design engineers had no idea of the cyl. head cracking issue when they came up with the viscous fan design. And in fact, the head may have no problem at all with temps over 100 C due to the fan not running. It would be interesting if someone would actually conduct experiments to see if the head will crack at high temps. It would be necessary to use a number of heads to get usable results $$$. But that's another issue. Anyway, for us folks living in high heat areas, It makes sense to run the fan before its design temps. My fan would stop within aprox. 2 turns (but still not couple tight when hot) and it would spin free when cold. It would never make any discernable noise over the clatter. So i put in the viscous fluid from Toyota in hopes that it would basically couple all the time. Will soon find out after I get it all back together.

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1981 240D
1987 300D Turbo
1973 220
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