How To Change Mercedes Benz Water Temperature Sensor
How to change Mercedes Benz Water Temperature Sensor and Water Temperature Sender Sensor.
Vehicle is a 1995 Mercedes Benz S420 W140, V8 4.2 liter engine. Problems are faulty water temperature senor and water temperature sender sensor.
Symptoms Of Failed Temperature Sensor Mercedes S420
Mercedes Benz S420 runs and drives fine when cold but loses engine power completely when engine reaches normal operating temperature (car becomes undrivable after 20 minutes or so). Symptoms might be mistaken for misfire or overheating but are caused by failure of water temperature sensor and temperature sender sensor.
Water temperature gauge on instrument cluster might not work at all or show a much lower coolant temperature than it should when engine is at normal operating temperature. No Check Engine light or other trouble lights illuminated.
Tools: Ratchet, extension, deep 19mm socket and 24mm socket.
How to change Mercedes Benz Water Temperature Sensor and Water Temperature Sender Sensor. Time to finish: 30 minutes at most, sensors are quite accessible and easily removed or installed. Both sensors are inexpensive, about $30 each. Sensors should be changed when engine is cold, there will be very little to no coolant leak when removing old sensors and installing new ones.
Make sure to check Mercedes Benz coolant sensors visually or by part number before ordering new parts as on later models of W140 sensors might be different from earlier models.
Start by removing front part of engine cover. Pull it upwards and it will come off.
How To Remove Temperature Sensor
Mercedes Benz Water Temperature Sensor and Water Temperature Sender Sensor are located on top of the engine up front, very easy to reach and change.
Green arrow shown water temperature sender and red arrow shows water temperature sensor (image above).
Remove water temperature sensors electrical connections, just pull on them upwards and will come off. Use 19mm socket to remove coolant temperature sender first and then proceed to remove coolant temperature sensor using 24mm socket.
How to Install Mercedes Benz Water Temperature Sensor and Water Temperature Sender Sensor:
Make sure old o-rings washers do not remain stuck on engine block, new sensors come with new o-ring washers. Apply grease on new sensor threads prior to installation. Install water temperature sensor first and then water temperature sender, ensure both sensors are tighten properly. Do not over tighten new sensors on installation, just tight enough.
Push both electrical connection on sensors and start the car. Start the car and leave it running until normal operating temperature is reached to ascertain there are no coolant leaks or other problems. Install engine cover and you are done.
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