I am relatively new here and not yet totally familiar with F4's. But an engine is an engine and they all operate under the same conditions. From reading the thread it would appear that the F4 has a bit of a problem with running hot though I can't confirm this as I haven't ridden my bike yet. Pa. Cold. I'm old. The thread on a modified water pump impeller is interesting and appears to lower the coolant temp somewhat by speeding up the coolant flow. However there is a limit as to how fast the coolant can flow as it needs a certain amount of "dwell" time in the radiator to extract the max amount of heat. I am thinking that the overheating is more due to insufficient radiator area than flow speed. I also wonder about the thermostat's opening temp. Does anyone know what it is? It is my feeling that a solution would be to increase rad area. The only way I can see to do this would to be to install a thicker rad or add an additional smaller rad in front of the existing one. Which would involve mounting and plumbing issues that are easily overcome. I also wonder if a lower opening temp thermostat wouldn't help as well. Any comments or feelings on this?