I've got one idea. A couple years ago, I had a similar problem, and went to the dealership 3 times for it, until finally figured out a solution with the mechanic.
This may or may not be your problem. But just in case, CLEAN that radiator! In my 700 the fins just weren't clean enough. So, I've started using Eagle One Mag Cleaner for alloy wheels. Spray directly into the fins, and let it sit a few minutes. I was very surprised to see the amount of dirt that came out when I flushed it out.
don't get it on painted areas or plastic! it's some rough stuff. Maybe this will help.