PeachParts Mercedes-Benz Forum - View Single Post

duxthe1 · #1 07-06-2020, 11:00 PM

I completely ditched the fan clutch and aux fans out front in my CE. I modified a 600W 203ch fan for a 124 shroud and built a controller for it. This allowed using a later style refrigerant temperature sensor instead of a pressure switch. I found out a couple of things along the way.

When dialing in the code for my fan module I found that I could run the fan full speed and still overheat sitting in traffic. Airflow was not the limiting factor. I found that if I held the accelerator to give a 750-800 RPM idle speed I could watch the temp gauge fall back to thermostat set point. At the ~600 RPM hot idle speed, there was insufficient coolant being circulated to handle a high heat load. I've been tuning the CIS module in my coupe and have electronically raised the idle speed. With these mods I never overheat. Absolute worst case scenario I see 93C, and am probably one of the coolest running 124s around. It took extraordinary measures to achieve this.

Without going down the rabbit hole to join me, there are a few things that can help. Gotta have a good fan clutch. Also need good airflow through the radiator. These cars are old enough that its a sure bet there is plenty of trash in bottom of the aux fan shroud blocking a fair percentage of it. Accumulation of dirt and crud in the condenser and radiator fins is costing heat transfer too. These cars need a full a/c charge.
I've seen cars that would cool but didn't have enough pressure to trigger the fans, resulting in overheating. Check the rotation direction of the aux fans. For the longest time replacement fans have had the wiring reversed in the connector. Many half assed techs have missed that detail. Lastly learn to accept that the system was marginal to begin with, and age doesn't make them better.