well im putting my money on the cavitating water pump and collapsing bottom radiator hose seeing as a suby race team had that problem. instead of just replacing the hose though, i would like to replace the water pump as well just in case that has also gone bad. and because my thermostat is drilled I would like to replace that as well. Also, an external oil cooler can't hurt. For the way I beat on the car on the track, it is definitely a safety precaution.