I have a 2018 E300 and since last winter I found that the engine temperature is not stable, it will drop down, warm back to normal and drop down again which leads higher fuel consumption and unstable warm air during winter.

I changed thermostats but nothing happened. The other guy who had exact same issue with me he finally updated his ECU or computer systems and the problem solved, I wonder if anyone have any idea on how much the dealer charges for this kind service?

 

very interesting topic.

Beware that the Display Instrument Panel shows computed temps, not actual sensor ie. doctored by ECU.

With a new thermostat your engine coolant is being well circulated.

Repair charges should be less than $350 with troubleshooting fee and actual programming steps plus carwash.

Let us know if the latest ECU firmware shows smooth temps. Coolant temp may be affected by pistons storing heat instead of being oil sprayed at normal driving RPM - See this thread for favorable oiling solutions...
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