I have a 92 300E and 93 400E that both seem to run a little on the warm side, especially at idle. They both have radiators that are less than a year old. Neck snapped off on the 300e and the fan clutch went on the 400e and threw the fan into the radiator (you should have heard how that sounded!!)
I haven't had any overheating problems yet but I do keep a concerned eye on them. The 300E did fine at idle in the heat today and it is 100+ here. The thermostat reading usually never goes above 100 on the console. I guess it is up to you but just keep an eye on it.
1991 190E (decommissioned)