dieselnut

I was replacing fuel filter on my 2012 ML350 BlueTec, when I noticed that thermostat is missing temperature sensor on top (its black plastic electrical connector is seen on top of 365 picture, attached). Strange, but I also found loose, but capped electrical connector with wire harness length matching sensor location. Part number for thermostat is 6422001615 On part diagram I don't see separate part number for the sensor, not sure if sensor is shown on the drawing either. Car works fine, displays coolant temperature on dash, no OBD2 warnings or console messages, no SEL. I wonder if someone knows whether this sensor can be purchased separately. Is there a part# for it? Should it be installed on 2012 ml350 bluetec model? Last pic shows that it was installed on 2011 model. Air inlet and charge pipe look like on prev. gen of OM642 installed on W164). But part# is, I think, the same for W164 and W166.
Thank you for your expertise in this matter

jrsmith_68

That is not a sensor. What looks like a sensor on the other thermostat you see is actually a heater, some thermostats are electrically controlled, meaning the ECM can open the thermostat sooner. I would guess that the function was designed out for cost savings and the harness has not caught up.

dieselnut

jrsmith_68, Thank you for taking time to reply. Interesting that I cannot find this part without position regulator.

samaritrey

That is strange but I don't think the car monitors it as my car had the connector break off and I never had a CEL. I did JBweld it back on but mostly did that to keep the connector somewhere safe.
Do you have any records of any thermostat work ever being done?

dieselnut

@samaritrey, No I bought this car from a car auction with no service book or records. It's still on warranty. Judging by time stamps on consumable parts (filters), previous owner, religiously followed maintenance intervals at MB dealer (OEM brake pads). Also looking at engine compartment I didn't find any evidence that any major repair work was done on the engine.