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Hey guys,
First of all, I wouldn't undertake something like this if you are not comfortable programming a micro computer of some sort, like an Motorola HC11.
Your effots could be put in a better place, like switching over to a manual rack and pinion steering, or plug in battery w/ alternator field kill switch.
I know a bit about electric water pumps. They make sense, mostly on the HEV's I work on for my job. They can run at optimum speeds, instead of just engine speed. Typically coolant pumps on gasoline ICEs actually rely on cavation to limit pump flow!! in order to control e-pumps well, you need to know where you water temp sensor is, and the transfer function for the sensor. You set some minimum flow, say about 0.1 gpm. This will help the engine warm up much faster. There needs to be a target engine coolant temp, say 190F, but below the threshold for radiator fan operation. Use these as your bounds and tune a PID to run a small brushed motor controller that has a 0-5V input.
So here is the non-propriety data: The real benefit to using a E-pump is the elimination of the belt all together. Most modern HEV's already have e-power steering and e-Air Cond. In an HEV, the alternator is redundant, and not present, that leaves the water pump on the belt. The belt, all by itself uses 2-3 HP with no load on it, but that load is pretty constant and doesn't change. Switching to an e-pump allows you to shed that load.
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