hpeer wrote in news:494ed38b$0$5541
:

I do (at least at times) get water flow through the system with the
engine off. This MUST be due to a siphon effect. I can't swear that it
happens when I am having the overheating problem.



There you go. You don't want ANY water system aboard depending on
something running on a siphon to make it go. That's just an accident
waiting to happen.