I'm from Brown University and this is my second year on the team but my first year actually doing design work. I'm not a powertrain expert by any means, but I'm pretty sure that the engine power is divided among the exhaust, coolant/oil (someone else is doing oil on my team), and the drivetrain itself. Since horsepower is positively correlated with RPM, RPM should be the primary driver of heat to the radiator, but I'm having a hard time figuring out how that might be effected by other factors, unless running the engine at high rpm at idle means that power is going out the exhaust and water hose instead of the drivetrain. I can talk to our team's powertrain people about it.