01, the capability of a water pump is determined by something called "Head". It can pump water a long ways and uphill a little bit or it can pump a little ways and uphill a lot more. In a typical system, water does not go very far and it goes uphill the height of the radiator. Looking at Jim's diagram, water must be pumped twice the height of the radiator and farther as well, doubling the head requirement. Having said that and knowing a little about GM mechanical pumps, increasing the head requirement from 2 to 4 when the rating is 12 doesn't make much difference. The thermostat will more determine the amount of water flowing. As I have said earlier, removing the thermostat lets water flow too fast for cooling. Also everyone pay close attention to what Jim is saying about the radiator caps. There are vented and non-vented and they look just alike but the correct one must be used.