OM642 350d Thermostat temperature

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Jan 16, 2017
A238 E350d 4Matic CABRIOLET 2018
Hi, I have been watching my engine temperature the last few days. I have a 2018 E Class Cabriolet 4-matic with the 350d OM642 engine. This has replaced my 2013 E Class Cabriolet which had the earlier EURO5 OM642 engine.

The temperature gauge in the dash gets up to 90 after about 5 miles (5 minutes) driving and sits there all day.
However, when I view the 'engine data' in Comand, when the dash first shows 90, it's actually only reached 55. It then takes an a further 15-20 minutes to get up to 80 and if I sit in traffic or boot it uphill, the temperature will reach 85.

I suspect the thermostat is faulty, which seems a bit rubbish on a car that is 4 years old and has only done 24k miles.
Am I correct, or is this normal when the outside temperature is 7-8C?

I would have a go at changing it myself, but it's buried under a load of plastic on the EURO6 OM642 engine, instead of in plain sight as with my old one.
I have an iCarSoft CR Pro and I tried using that to view the live data from the Engine ECU to verify that the Comand temperature display is accurate.. but I don't have the option to view data which is a shame (it worked on the old car OK)..
Are you sure that’s not oil temp you are viewing??

I’d get some way of viewing the actual value of the coolant temp and compare to the gauge.
Use the OBD/EOBD mode rather than the Mercedes mode on the icarsoft, very likely coolant temp will be available there.
Or grab an OBD2 to Bluetooth adapter and an app like torque ?
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The ECU will be getting the temperature from the same place and transmitting to the temp gauge and Comand. Why they are telling you different is the mystery.

On Torque you could monitor the coolant temp and oil temp and on some ATF side by side. It might tell you Comand is monitoring oil, or even ATF??
Yes, Command shows the oil temperature. Which makes perfect sense. I should be pleased that it never gets high.

I wonder what sort of an idiot I am. I'll get back in my box.
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