Can't see how you can run them dry. They rely on the water for lubrication and cooling and in turn the engine relys on the water for its cooling. So if they run dry the engines going to overheat. Whats the point of running them dry!!
I have used them in the past no probs and it is nice to have that extra insurance in case of a blockage in the water inlet I got mine from AMC DIESEL near Preston Tel 01772 613003