When I first bought mine (83 300D), it had green coolant and slooooowly crept up to ~70C (stuck thermostat).


I replaced the thermostat with an 85C unit and switched to G05 (no citrus flush, just a hose). Mine now sits around 88-94C fully warmed up. Never breaks 99C, even when going up big steep hills @75mph for ~5min.


Probably shouldve gone with an 80C thermostat... and my secondary fan doesnt work, and my fan clutch is likely getting long in the tooth, and the radiator likely has sediment/build up... and yeah, its warmer than I'd like, but I'm not worried by those temps either.


(and these temps are from the instrument gauge, which could be inaccurate ... good idea to verify the temps... I just need to follow my own advice.)


I'd say if it ever breaks 100C, keep an eye on it. If you get consistent temps at ~100C, prepare to work on it. If it breaks 110C, pull it over or get home ASAP. Approaching 120C? You should already be pulled over and ready to turn it off.