I am trying to track down a running hot problem and I am replacing the fan clutch.

A guy at Sun Valley Dismantlers was telling me that the fan clutches are mostly for the stop and go driving and that over 2500 rpms the fan spins freely, not stuck to the crankshaft. The clutch disengages.

Is this correct?

I have pretty much replaced or ruled everything else out.

I have had a couple mechanics check the fan clutch and tell me it is working, but the tests people have told me to do to check it seem so subjective.

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1965 220SEb Manual

I think the disengagement above 2500 rpm was a feature on the V8 fan clutches. They are also significantly more expensive than those for the 6 cyls.

The 6 cyl fan clutches do have a pin with a bi-metallic spring that pushes on the pin and changes the viscous coupling as a function of temperature such that when it is hot, the mechanical coupling is tighter and the fan turns closer to the speed of the pulley side of the clutch.

These things are not the easiest things to diagnose.

One method I've heard of is that when the car is idling, it should be somewhat hard to stop the fan. One has to be careful on this test. You wrap a shop rag around your hand and push flat-palmed against the BACKSIDE of the fan to get an idea of how hard it is to stop the turning of the fan.

A pretty inexact test, but it can give you an idea of whether there is a problem.

If the cooling problem is at freeway speeds, then I would suspect the radiator or thermostat rather than the fan.

If your car started running hot fairly suddenly, and still runs fine (ignition not way off - which can also cause hot running), I would suspect a hanging thermostat. Other option could be busted waterpump (pully or impeller slipping over shaft). Also, don't forget to check waterpump belt tension. Belt may be slipping causing pump not to work properly. Check that first.

Other weird thing that I am not sure can happen on MB is that the fan is mounted the wrong way around (seen it on some British cars where owners/mechanics reversed fan blades or switched polarity causing electric fans to push air through grille away from car...)

Bert

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'70 111 280SE/c 3.5 (4 spd manual) - sold
'63 MGB
'73 MGBGT V8

I don't think you could get it backwards.

I thought all fan clutches disengaged at higher rpm.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have a similar problem and just purchased a new fan clutch myself. I believe there are two kinds with the same number, I'm not sure if they function the same. One of them is the expensive Behr brand, presumably original Mercedes part, and the cheapest place I found was ******** for $180 or so. Others charge more than $200 for them. These fans have a rectangular strip along the back side and thin closely spaced long fins.

The other type is the kind many people are offering new on ebay, these are a "whatever" brand and have a spiral spring in the center of them and some have widely spaced fins, others not. They all go under the same part number, but reputable mercedes parts dealers all show the more expensive Behr fan for the same applications. I'm not sure if these cheaper (~$30 at ********) fans will work the same way or not. There is a used Behr version on ebay right now with the fan still attached for around $10 I believe, who knows if it works though.

With all this disclaimer out of the way, the fan I was shipped has a definite resistance uninstalled, I can feel the clutch pull through the liquid inside. My problem was different in that my car runs cool and happy under most conditions except EXTREME traffic jams going through the big dig on hot humid days, in which the temp creeps up and I hear no fan engaging whatsoever. In addition, when I have stopped and checked the fan, it feels the same as when the car is cold (only slight resistance) It appears that the clutch installed in my car is original and is the same as the Behr unit I received. The one in the car definitely slips at high revs, my car lives at high revvs and I hear no fan roaring at all. I'm pretty sensitive to these sounds as I had a locked up fan clutch on an Olds wagon once which barely revved over 3k most of the time with the slushbox. I plan on installing the new unit sometime in the next few days. I will report back with the results.

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1967 230S automatic
Boston, MA

this might help
http://mbca.cartama.net/showthread.php?t=25224&highlight=fan

You may want to think about an electric fan for the really hot days. Mount up a toggle switch.

I got the new Behr fan clutch installed last night. The original one was identical except that it was caked in dirt and oil all over the radiator-facing side. I think that this sludgy dirt was preventing the bimetallic strip from moving and thus the hi-temp engagement of the fan. I'm guessing that the gunk came out of the clutch itself, although it still feels just like the replacement when turned. Perhaps if it was cleaned it would work properly.

The original fan itself is a nicely made six blade unit and is also Behr brand, the part number is embossed on it and begins with "108". In fact, I was impressed with the whole assembly, the one let-down being those four 10mm bolts. I managed not to round any of them but even the Sears 6 pt closed end wrenches I used moved more than I would've liked and the wrench *just barely* cleared the sides of the fan clutch and I had to wrangle it into place. The bolts are really more of a 9.5 or 9.8mm I'd say.

Regardless, the whole job took only 30 mins max. It would've been even easier if it wasn't for those awkward bolts.

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1967 230S automatic
Boston, MA

You have several options. For my V8, I bought one off ebay for 116 USD. I also bought one for 68 USD off ebay for my L6 benz. They both work nicely.

In fact, I used to have a steady overheating problem in my V8. It was solved by replacing the overflow tank cap, some leaking coolant hoses, and putting a new fan clutch in.

To figure out what kind of overheating problems you're having you have to understand how it approaches high temp. Does it slowly creep up? Does it instantly reach high temps and then decline just as fast with moderate throttle depression?

The first indicates a poor heat transfer situation which is typically linked to poor air flow/coolant flow. So the suggestion above that you have a week water pump could be right. However, I'd change the fan clutch first before removing the hoses and accessories. That'd involve changing a couple of expensive funny shaped gaskets.

The second symptom indicates a coolant leak. Air/coolant systems require consistent pressure at the cap. The pressure translates into higher exchange capacity at the radiator. If the system vents at a particular point (i.e: leaks), then the super heated vapor is let down before it can reach the radiator and it becomes a saturated liquid/vapor mixture. In short, you lose heat exchange capacity so pressure test your system. I used to not invest in putting ultra pure water into my radiator system, but after working with ultra pure and not-so-pure water I've learned that there is a significant difference in its heat capacity when doped with whatever amount of pure antifreeze.

-Troy

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- - - '77 federal 280e - 222k miles
- - - '85 380se - 129k miles
- - - '07 Chevy truck
- - - '79 Datsun 280zx with '82 turbo motor
- - - Currently looking for a clean 190e with less than 160k miles.

IIRC those 10 mm bolts are so close to the hub that you really need to take a little material off the part of the wrench that goes around the outside of the bolt head to clear it.

I have a lot of wrenches with material ground off here and there tailored for specific jobs.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have replaced the thermostat, water pump, tested the temp gauge, replaced and rodded the radiator, replaced the cap, and my timing is right.

The only thing left is the fan clutch as far as I can tell. It is starting to heat up again now that the weather is warming up. We haven't been above 80 degrees yet here in Fort Collins, CO.

I haven't done a proper test yet this year, but I was climbing a hill last week and the gauge started climbing as well. I drove out on the highway and the temp crept up slowly to near 200 degrees. When I slowed down the temp came down pretty quick too. So far it doesn't seem to be overheating in stop and go, but I don't think it is hot enough outside yet.

Any consensus yet on whether the clutch disengages at high RPMs?

This is my '68 230s automatic.

Eddie

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1965 220SEb Manual

I've been around town lately getting insight on a slight cooling problem I had in my 280e and the consenus amongst the garage technicians I've spoken to is that the fan clutch is a thermostatic device and regardless of engine speed, the fan clutch is supposed to clutch at certain temperatures for the sake of cooling and not at others. Just like your thermostat, a filament heats up and expands causing the shaft to ever so slightly move in the lateral direction into the fluid medium. Thus results friction against the fluid trapped inbetween the clutch and the shaft. If you think about it too much, you can convince yourself that its supposed to slip more at high speed because of fluid boundary layers in narrow spaces, but that's a lesson in fluid dynamics we don't need in order to solve your problem.

I'd definitely say if you started climbing a hill (putting strain on the drivetrain) and the temp jumped, then you've got a cooling load/heat removal issue which means the fan's not working since you've already replaced the pump.

Given everything you've already done, I'd say it must be the fan clutch. Get it up to temp and see how much resistance it holds. Obviously, shut off the engine at temp and feel the resistance in the clutch. If its a new clutch, it could very well be defective. I had one before finally getting a good one for my 280e.

Also, pressure test your system. A coolant leak can cause the strangest heating/cooling phenomena. See my above post for an explanation on why.

-Troy

__________________
- - - '77 federal 280e - 222k miles
- - - '85 380se - 129k miles
- - - '07 Chevy truck
- - - '79 Datsun 280zx with '82 turbo motor
- - - Currently looking for a clean 190e with less than 160k miles.

Yup, open end or grind a box end. Tedious job....

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

I agree w/the others that this problem is the fan clutch. From the W123 cars and on, a magnetic clutch is used and tested by turning the fan - w/the engine off - and noting some resistence. From the W115 cars on back a temperature-viscous clutch is used. It can be checked by running the engine from 4000 to 4500 RPM; a distinct change of fan sound should be heard when reaching this RPM. Attempting to stick something in the fan blades w/the engine running is insane. Don't do it!

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Don't Chrome them; polish them

I live in Tucson. The saying here is, "It ain't exactly as hot as Hell here in the summer but you can SEE it from here"! That being said, the only fan I use here on all my cars is an electric aftermarket fan. Throw those damn clutch fans away! If you have a V-8 you can be forgiven for using a "flex" fan along with an electric but any clutch fan over three years old is suspect at best.

Mill Supply has a nice selection of fans and adjustable thermostatic actuators. They deal mostly with step vans but they also have a nice selection of restoration items for older cars.