One problem related to cooling fan has been reported for the 2006 Mercedes Benz E350. The most recently reported issues are listed below.
I arrived home after driving 2 miles from work and when I stopped I saw smoke coming from the engine. I turned off the car and opened the hood. The smoke would almost stop and then become thick again, in cycles of about 1 minute. The smoke was coming from the cooling fan. After several cycles it burst into flames. Fortunately we were ready with a fire extinguisher and put the fire out right away. The fuse, which I believe should have popped and stopped the cycling of the fan, never did blow. I bought my car used but it only has 50,000 miles on it. All information in the carfax indicates it was maintained. I didn't take pictures of the fire.