E320 FAN comes on does not go off. Engine is about to overheat

Yes, it's not complicated for folks who have workshop manuals, fully capable diagnostic equipment, and have experience working on these vehicles. Clearly "changing the fan" was a guess that did not yield any positive results, but certainly cost some wasted money. Consider investing in professional testing that will get you the answers you need. There's nothing anyone online here can offer other than a multitude of guesses, which do nothing without hands on testing to see what is really happening. www.repairpal.com/repair-shops