What he said. On the OM603 you can get a smaller water pump pulley to spin the pump faster at idle. A similar pulley is available for the m103/m104. Between the small water pump pulley and electric puller fans behind the radiator, it completely fixed my overhearing issue especially at idle. A mechanical fan can only spin as fast as the engine. An electric puller fan can run max speed at idle. It never exceeds 90c now.


Prius electric fans retrofitted to the pull air through the w124 radiator. It ain't pretty but it works.

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CENSORED due to not family friendly words

Go with the 600 watt newer C/E/S class fan. I did this set up about 2 years ago and my car will sit at about 90*C, with the a/c on, not moving, with an ambient outside temp of about 117*F. You can ditch the 2 aux fans in the front also as they just impede air flow. Here is a link of the car idling with the a/c on in about 120*F weather: https://photos.google.com/share/AF1QipOGtBKmZsfng_qahECam5Ob8hq11c3QS-Fmx0O_00L0QurjMsMHxNGRCL_FjLfnKQ/photo/AF1QipNwhqn_TJuox57Zfcbe2gGQ1bu8iITOAEzIw1qe?key=RXZYZUNlTUlJd1o0dmFSV0YyM3JoRWJVOFFLOW53

Also here is the thread I created a while back while on the hunt for the perfect cooling system for the m103: Newer MB 600 watt electrical fan in a m103

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1990 190E 3.0L

Theres a reason MB ditched the clutch fan and went all electric. Theres a few probs. I had the issue of overheat with AC on. Litereally every thing new, OEM parts. All behr stuff. Figured out that with AC on my fan clutch was clutching agressively at idle which causes condenser to cool enough to never kick the high side switch on. So AC is happy while your engine is cooking basically. Probably my brand new OEM switch is just junk and not kicking on at the right temp. So I wired a relay to turn on the low speed aux fan circuit whenever the clutch is engaged. This helped a lot to keep the system from running away, especially after getting off freeway. Interestingly enough if your system has low refrigerant this switch will not kick on and your car will run hotter as well, so make sure you got a proper charge if you use the AC. I also removed the plastic cover from the front of the condenser and cut bottom half off. This blocks a massive amount of airflow from the bumper when the vehicle is in motion, I noticed lower freeway temps after this.

All this helped but I'm kind of crazy so I fabbed up a bracket to mount an all brass ford heater core in the wheel well with a spal 5.5 inch fan on it. Now literally nothing will make it go above 100 with AC on. Still wish it would just sit at 80C like a newer mercedes but I guess that's the power of a 900 watt fan and feedback loop speed controller. I thought about it but theres very little room on my 300CE for a fan behind the radiator and I'd need to upgrade the alternator as well.

I think if I could just get a smaller diameter fan pulley Id be able to move more heat than all the mods Ive done so far but I can't seem to find anything even close that would work. That's the real ticket IMO, just move more air at idle from the clutch fan. ACM clutches are also "aggressive".

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1981 300SD 512k OM603

If its the same quality as the BEHR found on the 95 E300, then its a poor excuse of a fan clutch, I actually refilled the fan clutch of my old E300D with a thicker oil and got great results, uptil the time I changed it for a sachs branded one.

The fan was extremely loud when locked on, I think the original fluid in the clutch is too thin and causes too much slip and leaks too easy.

The guy whose W124 E320 I helped with had a sachs/horton clutch installed by me on his car and it was perfect - I had to use compressed air to clean the condenser fins and also washed it off of some non-corrosive condenser coil cleaner to remove road grease from it. This work definitely improved airflow a great deal lot.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Have you had the cooling system pressure tested?


These are old cars. Water pumps have probably deteriorated on all three cars.
I've had the same problem on W124's I've owned and then made the misfortune to install a cheap PRC water pump. Replacing a water pump on the M103 is a job you only want top do once.


After two less than effective pumps I bit the bullet and installed an OEM Graf. Never had an issue after. Even 40+ degree (110F) days, the auxiliary fan hardly came in.

And I'll put my habd up as well and recommend the Sachs fan. Beware there are a lot of cheap fan knockoffs with the Behr name on them.

even the original slim type behr clutch is useless, to make it work you need to fill it with 12000 cst oil, otherwise it doesnt engage.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)