Flushing the cooling system (Mercedes-Benz E-Class W123)

Over time, the radiator and engine water passages become narrowed or even completely clogged with scale or deposits, which reduces the efficiency of the cooling system. In this case, the coolant becomes dark and rusty, and the entire system needs to be flushed. In case of severe clogging, backwashing may be required.

1. Disconnect the upper hose from the radiator, then insert a water hose and flush the radiator with a circulating stream until the water coming out of the drain hole is clean and clear. For better flushing, disconnect the lower hose from the radiator.

2. If the system is heavily clogged, it should be flushed with a counter-current. To do this, remove the radiator, turn it over and insert a hose into its outlet. Flush until the water flowing out of the filler hole is clear.

3. The engine should also be flushed. To do this, remove the thermostat. Insert a hose into the water passage leading from the thermostat housing to the cylinder head and continue flushing until the water flowing out of the cylinder block drain plug and from the lower hose is clear. Also disconnect and flush the hoses leading to the carburetor or intake manifold (depending on the design).

4. Chemical cleaners should only be used as a last resort. Regular replacement of the coolant prevents contamination of the system.

[Article borrowed from the web portal: mercedesman]