Have you tried "burping" the cooling system to get the air out?

When is the car overheating?

If it is OK at highway speeds, then the radiator is probably OK. If not, then you should get it rodded out as Gympie suggests.

If the problem is at idle, then the water pump or fan are suspect.

There is a monster post on the main forum that concerns a 420SEL that was overheating that discusses every conceivable cooling problem. You might do a search there.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe