Richard just added an [electric water pump] and [electric fan] to his engine, and would like some finer control over the system.
This particular engine runs a 17 Amp fan, and a 7.5 Amp water pump. PWM speed control of these components looks ideal.
Do you have 2 free FET outputs (almost certainly) that you can parallel to drive that safely? (the econoseal pin is also for 10A only at higher temps of its range)
Maybe it should increase pump flow rate based on engine coolant temp measured at the heads, and increase fan speed based on coolant temp drop across the radiator. There may have to be some fuzzy logic or something to adapt to the different thermal transfer rates of various radiators and engines, and the flow rates of various pumps.
The coolant systems have such a high thermal mass, and low precision requirements (who cares if temp changes +-1 C?), that any refined control has only marginal benefits. The simple radiator bypass valve and fan on/off is quite efficient and works well but if you enjoy playing with it...
I'd definitely put energy into BoostController instead, where there is a lot of places for improvement (handling, TPS dependence, rampup and peak, changing settings easily etc...) .