HI, I have been driving 2011 ML63 for 6 years now and the temperature was always, essentially, constant 95 celsius. Never when up by 2 or down by 2. Over the past 6 months I noticed the temperature would slowly decrease so that driving in Miami in 90 degree (fahrenheit) the coolant temp would be 92 celcius for example. Turns out the thermostat was failing in the open position. I just had a new one put in and now when I drive the temp gauge is all over the place. It can now range from 85-120 celsius.

Today for example I was at a traffic light and the coolant temp hit 120 and then started to slowly decrease to 95. Another time I entered the freeway and the coolant temp dropped to 85.

The shop says this is normal for the M156, I checked the manual and that is correct. I, however, have never seen my gauge move like this while driving the car.

Can some other owners let me know your experiences, I pamper this car, its my daily driver and don't want to damage the engine obviously.

In the end I suppose I am looking for some reassurance and wonder why the gauge never acted in this manner for previous 6 years of ownership.

thanks in advance
ML63 driver

 

Something isn't right, My coolant temps would be stuck on 91-92 no matter what way i drive

 

My 2010 sits pretty consistently at 199-200F or around 92C also. Oil temp is more variable.

 

The shop did not evacuate all the air out the system properly.

They used the old fashioned way of turning on the car and heat and letting the air bubbles come out. This does not work on the ML for some reason.

Once that air pockets were removed properly it works like it should and coolant temp is constant 98 now.