C350 CDI om642 correct engine temperature?

[borntobemild]

Hi there, Got my E350 cdi W212 a few weeks ago and temperature was not reaching 'normal'. Told garage to change the thermostat and it now runs up to 90 and sits there all day whether in traffic or on a motorway. Believe the guys and gals on the forum and not MB specialist as the people on here have thousands of hours more experience collectively than any mechanic can.