Hi Arthur,

By switching the heating up to high and turning the interior fans full blast, this reduces the engine temperature - drastically - down towards normal operating temp (87c).

I've tried two other thermostats - one brand new (off market Wahler) The other OEM so new it still shines. On freeway the temperature is too low - way under 80 degrees C. On idling will gradually creep up to 115+. I assumed (assumption being the mother of all screwups) that a new thermostat would solve this problem.

Maybe I need to get an original Behr thermostat.

The radiator is a new Behr unit. System has been bled. P.O. put green elcrappo fluid in. Had to change it too the new MB blue stuff. Another assumption suspected that P.O. had caused a problem with his cheap coolant.