When completely stuck in dead-stopped traffic (often 10-15 minutes to go a mile on Chicago expressways) in the summer, the hear used to go beyond normal. I never got to the red zone, but did have to shut it down and pull over for 1/2 hour a couple of times.
With water-wetter it never goes above normal. Even idling around Chicago Motor Speedway at last July's Sheetrock 400 parade lap (100 degrees, mega humidity, sitting at idle most of the time) the needle never moved. .....and no, the temp gauge isn't broken!
I had heard that WW can cause damage to some polymers (like plastic impellers and gaskets) but have had no problems at all. The rumors of damage may be urban legend, who knows....