Forget the above! They try, but there are some basic issues here that you should consider!

#1. Your car is almost 19 years old. If the radiator has not been replaced since 1987, I strongly recommend that you confirm that it circulates coolant as it was new, or replace it!

#2. Thermostats require periodic replacement. 5 to 8 years may be considered an active life span for effectively regulating engine temperatures.

#3. Fan clutch........or actually they are silicon filled and respond to predetermine temps that actuate the fan for pulling air through the radiator. They dont last forever and when worn do not pull air through the radiator as the designers planned. I just replaced mine!

#4. Auxiliary electric radiator fan. Actuated from a thermo switch, @ 105c, can fail to work if either the thermo switch is faulty, or the elect fan is faulty.

Figure that any of these parts become suspect automatically after 150K, or sooner.

By the sounds of you description, you are playing Russian roulette with you OM603 as these engine are particularly susceptible to overheat situations that usually result in $3K to $4k for repairs, as a result from overheating the engine that WILL catastrophically crack the aluminum head.

One exception, if unless the head has been replaced with the MB redesigned OM603 aluminum heads ...#17 thru #22, you need to seriously make sure your cooling system is 100%..............these OM603's in particular, the same as you have described here.............get with it, or it will let you down......Many many posts, threads here on this topic...............read.........BB