I normally let it idle until everything is rolled up and put back in the truck....helps get in moister out of the blower and cool it down some....as for the water temp...you are not going to hurt anything not cooling the water down..the hottest part of the water in coming out of the E-2 exchanger and pretty much straight to the solution lines.....not much there to cool down....
I do as Jim does, throttle down flip the water pump off, then let it idle while I roll up the hoses. It just seems to me that it would be better to let it cool off a bit before a shut down, kinda like the diesel.
I've gotten into the habit of running the temp down with the wand valve open till it drops to well below 180 - normally takes 2 - 3 minutes. Am I wasting my valuable time?? Ivebeensold