Mine runs ~82C all Winter and will creep up as temps increase. As long as it doesn't get too close to the red zone, >120C, the engine will be fine. Roughly 5-10% of the OM603.96 engines may experience head problems at some point in their lives. If the temps do climb close to the red zone, shut the engine down immediately! A common cause is a cracked radiator neck due to over torqueing of the spring clamp. There are very specifics specs for that clamp and fitting it properly requires the special MB tool.
'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold