What is normal running temperature? (300gd 1993 OM603)

My memory of a W463 dash board is foggy so I cannot visualise its layout. Never-the-less, the normal temparature is some 92° to 95° centigrade. Going by one description which I am not sure applies to you layout the temperature needle sits at the top loop of digit 8 of 80°. This translates to a closer reading of 90° in temperature. 

Your temperature reading should not rise more than 100° in temperature. On very hot days the needle will rise at idle but as you revv higher the viscous fan if working will kick in and you will hear a loud growling noise. If that is absent then the viscous coupling has failed - these are a common failure. Other possible causes for higher than normal reading is clogged radiator and worse case scenario - Head gasket breach.

Emergency measures to reduce heat is turn the interior temperature control to Hot and turn on heater fan full on. This will be uncomfortable but provides additional interal cooling area for the dissipation of excess heat from the engine. There is also a mechanical lock to permanentanly keep the fan engaged. Behind the viscous coupling you will notice that there are a series of lugs, bend on of these against the fan. You will need a longish screw driver to skillfully bend one of these tags. 

Water or oil temperature? Both will be higher in this weather which is 10C above normal for the time of year but easily coped with by the Mercs cooling system, the temp guage never shifts on mine once its up to 80C though mine is petrol