1992 Mercedes Benz 300d overheating

when you replace the radiator was the front of it very dirty? with debree? diesels will always cool off at an idle. I think the problem here is due to the extensive work on the cooling system. You air in the system, you are going to have to find a steep driveway or hill to put the car on open up the radiator cap, with the heater on, and see if you can get some air out.