Date registered: Dec 2005
Vehicle: W211 E320 Bluetec R129 SL500 - $1300 car ........ Ford F350 6l
Location: CA Bay Area
Mentioned: 9 Post(s)
Quoted: 1057 Post(s)
Diesels have lower settings than gassers. My newer diesel has thermostat opening at 75C and even driving on flat 80mph with 102F outside it stays below 80C.
Observe how the temperature change. From cold engine the temperature should pretty fast raise to thermostat opening point (again 75C on my diesel). Than it might slowly raise to full opening of the thermostat what is in 80-83C. Extreme loads might exceed the system cooling capacity and raise the temperature above 85, but if the engine stays at those temperatures all the time, something is not working the way it should.