[200hp/tonne]

Originally Posted by celek

Sure when you are working with a BMW pump that costs a fortune specifically engineered into the car, they can do it. My particular case I can not drop below 9v or the pump will not turn the water I already had the schematic drawn up with a FET to change voltage based off the ECT input value. Problem is the table of data tolerance would be so tight with the coolant temp sensor operating range of (</= 1.0v) - (>/=2.0v) = 9v-12v output.

Basically scaling a 1 vt temp range change for a 3v difference in range output

Could be done maybe this is how BMW is doing it.

BMW is most probably doing straight up pwm control based on xyz strategy in the engine ECU which could be based on just coolant temp or engine speed/load or both. You could just use one of the cheapest arduino controllers to read coolant temps and engine speed-load (directly or can bus) and hook up some sort of bridge circuit with FETs to pwm control the pump (as opposed to voltage control). This would give you freedom from the low voltage variation on the sensor and give u freedom to choose any control strategy. Sorry if i was too pedantic.