I am going to contradict myself here, well actually I am going to challenge ones thinking here...
1. If a thermostat is functioning correctly, what does a product like waterwetter actually have to do with lowering the temperature, would not the thermostat simply close up slightly to get the temp back up again? think about this.......
2. Memory is fading but I seem to remember popping the hood NOT to cool the engine , but to cool down the turbo, ( 1984 vw turbo-diesel 310,000 )
3. I seem to remember that years ago, some turbos where colled with water?, and or not oil.
4. I also remember that some model turbos did not have enough oil passing through them, which made them run very hot, and when the motor was shut down, they actually burned off the oil, and then ruined the turbo. I dont think this was Mercedes-Benz, but some other manufacturer, and most likely a gas engine.
98 300 DT