Mercedes Overheating Mercedes Benz 1991 350 SDL Overheating?

Mercedes Benz 1991 350 SDL Overheating? - mercedes overheating

We have a workshop and had several Mercedes 350SDL problems with overheating. Others have the radiator, which was replaced for a good while, but then began to overheat. He replaced the thermostat, clean the fins of the radiator and radiator and water pump. The problem persists.

Please give us the solution.