Mercedes: 1991 300E 2.6L overheating, antifreeze mixture, radiator shop

Question
History:  1991 300E, was given the car and now repairing it for my stepdaughter.  233K miles on it, some paperwork on history, but nothing on the engine overheating issue.  No water in oil, and head gasket appears to be fine.  
Finally got the car running after replacing the timing chain (long story) but noticed that it would overheat.  Flushed radiator and looks good.  Removed thermostat and ran it also, replaced thermostat.  Noticed that the Aux fans where not working and replaced them with a new temp control switch.  System works perfect.  BUT this is what happens.  The car will still start to overheat when at a idle, but holding the gas so the tack is showing 2.5K to 3 and it will then drop to below 80.  The water pump shows no visible signs of water leakage.  Was wondering if it is possible that the fins could have somehow been damaged and not pumping the water like it should.  Before I drop another buck on it, is there anyway possible to T/S the water pump.

Answer
Kevin,
When at idle,and the temp climbs to above 80 are the are the fans operating cool the radiator. If they are and you only get a drop by reving up the engine, I would suspect that the flutes in the radiator are restricted. With age salts can accumulate in the radiator and restrict the cooling surface. When you rev the engine that forces more coolant through the radiator. Also, it is important to have the proper antifreeze mixture in the water. And the pressure cap at the radiator need to be new. I would suggest you have a radiator shop look at the radiator.
Robert