Date registered: Dec 2010
Vehicle: 1973 450 SL
Mentioned: 15 Post(s)
Quoted: 378 Post(s)
The service manual recommends a mild detergent (degreaser) flush followed by a citric acid (again mild solution) flush.
I drained my cooling system first; radiator and block drains. My block drains were clogged with sludge. Then I ran water through it with the engine (water pump) running and only the radiator plug removed. I used a 'T' fitting at the heater inlet hose. I did this until I saw clear water coming out of the radiator. Next, I did the degreaser solution - this step is to prep for the citric acid. Finally, I ran the citric acid flush. I could not believe how much silty green gunk came out.
In the end, I chose the MB blue coolant mixed with distilled water.