My 1997 E420 has been running hot when I am stopped in traffic. By running hot I mean that the temperature steadily increases until I start moving and the RPMs increase. If I sit in traffic long enough it will exceed 120 degrees celsius. I recently replaced my auxiliary fans and everything seemed fine for a few days. Now my auxiliary fans are working, yet the temperature gauge starts climbing while idling and my auxiliary fans are kicking on sooner than they should and seem to be louder than before. I checked my thermostat and it appears to be working fine. I even removed the valve to make sure and the car runs fine when on the open road, but it still heats up when idling. I pulled the radiator hose while running the engine, at idle, the flow appeared very weak. As soon as I increased the RPMs the flow became much greater. My belief is that the water pump is worn, but it isn’t leaking. I ordered a new water pump and thermostat and plan on changing both. Just curious as to whether or not I am on the right track. Thanks.

 

i would make sure you got no air in the radiator, also clean the fins on the rad.
with some compressed air or water hose. that was my problem with my other car.

 

Replace the radiator cap as well. Could be weak. Back wash the radiator fins as mentioned above

 

how about the thermostat, if they stuck partially open it would create the same sympthoms.

 

Yeah, all of the above.

I can think of a number of things that will make it run hot. You'll have to eliminate the possibilties one a time.

Check the air intake hoses and rotomolds for cracks/leaks.

Blue