I was thinking about this the other day. Did the neck break off of the radiator? That is the most common failure. I was thinking that it may have an obstruction in the system somewhere. The other thing is possibly a bad thermostat out of the box? Can your technician help out somemore or is he out of solutions?

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM