Mercedes Engine Overheating Protection R129, R107, W124, W140, W201 Coolant Temperature Sensor Trick

How to replace your Benz coolant temperature sensor responsible for ensuring your car never overheats to the point that it can cause serious damage to your engine and head gasket. Video also covers a very common hack to trick your car into turning on the aux fans at a lower temperature. In doing, it keeps the engine temperature within a smaller range of acceptable temperatures.

The video was shot in March and the temperature was barely above freezing, so I could not get a chance to test the sensor and its modification. I will periodically post updates here. My car did not need the resistor hack, but I did it so I could share this knowledge and how-to via YouTube with the R129 global community. As always, I'm happy to share as much as I can with you.

Update: May 20 - Finally, very warm weather. The outside temperature was 30 Celsius (86 Fahrenheit) and the high speed aux fans kicked in a bit over 95C (reading from the instrument cluster). That's success.

Video applicable to most R129 SL, including the 500SL, 300SL, 320, most W124, W140, W201 and for many other 1980s and 1990s Mercedes-Benz, including those with KE-Jetronic.

ECT sensor (auxiliary fans) - air conditioning and extreme overheating protection (B10/8).
ECT part number: 008 542 4517 (Always check with your parts supplier for exact part for your make and model). Test your old sensor before buying.
Torque Specs: 25 NM
Sensor used in video: NTK (Made in Italy). Mercedes still makes it. Hella is also an excellent choice.

Resistor: 1000 Ohm, 1%, 1/4 Watt (Turns fans on at at about 90C)
Resistor: 1200 Ohm 1%, 1/4 Watt (Turns fans on at about 95C)
Note: Blue resistors usually heat resistant and better suited for engine bays, than other colors.
Note: Resistors can be soldered into place, once the desired resistor is found

Location of parts shown in the video will vary by model and year of car, but they are there.

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Car Shown: 1992 Mercedes-Benz 300SL (M104.980)

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Disclaimer - The content of this video is available for informational and educational purposes only. It is not intended to be a substitute for professional advice. I do my best to provide accurate and complete information, however, I assume no liability for any property or personal damage that may arise from any of the information contained in this video. Due to factors beyond the control of Handy Val, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Handy Val always recommends safe practices.