i see people are mentioning "coolant" on these follw-up answers. you can not use coolant I.E. antifreeze. this will raise your boiling point, giving you a hotter running engine, before the coolant circulates. be sure to use water only so the fluid will circulate at the proper temperatures, that is why it is called a thermosphin cooling system. using just water can cause corrision in the engine thus clogging the radiator. i use water with about 6oz water soluable oil to prevent corrision. i have never run a water pump.