Without knowing their design, it is hard to predict the junction temperature. My guess is that there might be a feedback loop in the design, whereby the flow rate of the coolant is increased (up to some maximum, of course) if the ambient temperature increases. 70C is a generally accepted "case temperature" of an electronic circuit board that processes power. In the water pump case, the circuit is likely to be a DC to AC converter (DC from battery and AC to drive the motor and to control its speed).
Last edited by queensfield; 08-18-2011 at 05:18 PM.
Reason: typed too fast