I hear there are four pumps, three electrical one mechanical, is any of the coolant on the inverter pump side connected in any way to the mechanical coolant pump side, or are they independent systems?
Totally separated. Radiator is the same but two sides of it are not connected at all. Inverter side just has one electrical pump. Engine side has mechanical pump for cooling the engine (and transfer the coolant when engine is running). Engine side also has heater electrical water pump it pumps coolant through heater core when heat is needed and engine is not running. And last the engine side (if you have North American Prius) has coolant thermos water pump. It pumps coolant to and from thermos (with coolant diverter valve) to store some engine heat after shutting down the Prius and before starting the engine at next startup of the Prius.
So the mechanical pump coolant flows through the radiator but the inverter pump fluid does not pass through the same radiator?
Radiator is a double radiator. One side of it (top side) is for for engine cooling and another side (bottom side) is for inverter cooling. Engine side is a lot bigger than inverter side. Two sides are not connected they are just build into the one radiator.
