If it's blowing on start up, I would think the breaker is just too fast. 10 amp on a coolant pump is huge, most pumps are in the 3-6 amp range. I would look in to a slower breaker, or a manual motor starter type. Is it a contactor mounted type or separate ? Have you checked to make sure all three legs are tight with no loose connections? What does the pump tag say for amps ?
http://www.grainger.com/Grainger/SCH...Y89?Pid=search
We typically use this type after the contactor, they are made for longer startup loads.