ps2cho, if you want, I still have my Spal electric puller you can try out and see if it works for you still pretty new, only had it for a year. If it works for you then you can buy it from me. Although, I did remove it because I didn't think it was keeping my temps low enough. I am using the viscous fan, which has done better.

Also, why is the Sachs clutch better or updated? There are only 2 things that I can think of what would make the Sachs better or updated, and that is either sooner flexing of the bimetallic strip....which would not mean anything unless the thermostat had opened up allowing the coolant into the radiator, or the viscosity of the silicone fluid has a higher weight. The latter would seem more likely as I have drained out a clutch and filled it with 30k silicone and when the clutch was locked, it was spinning at 100% of speed vs 80% with no slippage.

Not sure entirely but several people on the “other” forums have said the cut in temp is lower for the Sachs unit. I have also read the Behr clutches are quite flakey. For my situation and high ambient temps the lower therm and Sachs clutch is what ultimately worked.

Ok, so then the bimetallic strip flexes sooner allowing the clutch to lock up sooner. I wonder what the cut in temp is because if it is still before thermostat releases coolant to the radiator, I don't see how it would make much of a difference. On the other hand, running a 79C thermostat would most likely yield great results with the Sachs clutch.

The fan clutch for M103 doesn't engage until 95 C and even then it's not doing much when car is standing still in traffic.

Although I've never tried it, the fan clutch for 400E/E420 engages at a lower temp (around 82 C). If it fits the M103 motor it may be worth a try.

The easiest fix is to solder a 1K ohm resistor onto the coolant temp sensor. This way the signal to the auxilliary fan(s) is sent at around 90 C and not at 105 C.

Got a little news, guys... I can't swear to it until after I run it into town tomorrow evening, but a test run this evening with the thermostat from the 104 out of my 93 300E parts car seems to show a drastic improvement. I drove several miles at 60mph and then stopped. Temp yesterday shot above 100C in seconds. Barely touched 100 this time, and then after idling for a timed 4mins with the AC running at 72F setting when I immediately pulled off the highway to simulate a long traffic light. Less than a mile of 35-40mph brought the temp back to around 90C.

It has never come back down that quickly or crept up so slowly since the serious heat set in here in Alabama. I have been forced to shut off the AC at any traffic light to keep it under 110C and it was rare it dropped below 95C when I started movung again.

I didn't think to measure and compare the fine details of the two thermostats, but they were slightly different. The one I took out has "BTT/BTO Made in Germany" around the top of the body. The bypass plunger has "2.466 87 L6" stamped on the bottom. The plunger that closes the bypass port is 1.694" in diam and measures 1.125" from the bottom of the flange to the sealing surface of the plunger. The bypass port is 1.300" below the flange, so the plunger only moves 1.175" to close the bypass. The spring on the bypass plunger is VERY stiff. I think the thermostat is opening until the plunger seats on the bypass and then can't compress that spring enough to open further, restricting flow from the engine into the radiator.

The thermostat from the 93 had a noticeably smaller diameter plunger and it seemed shorter, so perhaps lets the thermostat open further when hot.

It will be wonderful if the solution is this simple. Will report back soon.

Typo above, the bypass plunger only moves .175", not 1.175".

Please do! I just looked on my maintenance doc and I am currently running a Behr 87C from 2014, so its 4 years old and has 50k on it. I am tempted to go buy a new thermostat, but I may hold out until you report back before purchasing to see if a later thermostat works better.

We can eliminate the fan clutch because if the cluthc was the issue, as soon as it engages and "roars", temps would drop fast, but on my 300TE it does not. It just stops it rising further, but never cools it down enough.

I never had good luck with the current generation of Behr clutches, not just MB limited. They are junk for BMWs too. Sachs set me back nearly $200 for the M103, but guess what? Works as designed. :)

Yup, I put the clutch from the 93 on my car, too. The fan cannot be stopped with a rag at idle when the engine is hot. The electric fans are operating correctly, too. It's something to do with the coolant not circulating and the thermostat is the only obvious obstruction in the system for the pump to overcome. If the thermostat isn't opening far enough, it would act exactly the way we are seeing.

Which Behr clutch have you guys used? There is a Chinese made one and a German made one. The German one is much better quality though idk if it locks up as well as the Sachs.

Just a curiosity, what kind of fuel mileage are you guys getting? I'm absolutely dead on 20mpg in the wagon no matter what.

I get 20.5-21.2mpg everywhere, city or freeway, every time. Maybe 21.8mpg in the winter w/o A/C on. Have for over a decade now. The one time it dipped to 15-16mpg was when my coil failed, so I knew something was wrong right away.

I have Genuine MB fan clutch thats only about a year old. Does not stop with newspaper. When my original clutch died, I replaced both Fan Clutch, bearing bracket and tensionr with Genuine MB pieces.
I also wonder if the 79C thermostat option would work better for us in HOT climates, because it will open earlier, and open wider the hotter it gets. It should theoretically do the same as you are trying to replicate with the other thermostat.

AFIK the m103 m104 om603 and om606 (all the 6 cyls) have the thinnest viscous fans of any W124s. Even the 5 cyl om602 runs a beefier viscous fan than the 6. I don't think a V8 fan will fit any 6.

I agree. I had the w124 fan on my 201, which has the 9 wide blades vs the 11 thin blades. However, in this case, it's not the fan that is triggering the cut in time at 95C it's the metal strip. So all that needs to be done is a simple swap of the bimetallic strip to have the viscous fan cut on at 82C vs 95C. But again, having the fan cut on at 82C means nothing unless the thermostat is also opening up sooner than the 87C. Otherwise he will just create extra drag on the engine for nothing. Even with the lower temp thermostat, if he is on the highway, the air moving through the radiator at speed would keep his temps low without modding the viscous fan, which I think was his original concern - doing highway speeds and having the temp creep up.

The wagon body makes a lot more aerodynamic drag than the sedan.what might be sufficient for a sedan might not on a wagon. I agree that at speed the viscous fan is irrelevant.