[fiveohpatrol]

pumping water "too fast" will not overheat an engine. If that were true, then it would be going just as fast through the engine, and not getting as much "heating time"

The most effective means of heat transfer is convection, where there is a fluid or gas moving over a surface, and the faster it goes, the BETTER the heat transfer. Since the fluid in this case would be moving faster, it would effectively be removing more heat.