ps2cho,
I too have a couple of 124's, one being a E420. I noticed a difference in radiator size from my 320CE, it being smaller. But then I noticed that the radiator frame of both cars was the same, telling me I can install the larger radiator in the CE. My E420 never gets overheated.
An old mechanic told me years ago that one should never run their engine below 200F. He said that the oil runs hotter and if there is any condensation in the crankcase it would turn to sulfuric acid at lower temps. True?, don't know but it makes sense.
Anziani