If you are blowing that much coolant out of the radiator, you probably have a blown head gasket. If you haven't recently serviced the top-end (meaning you may have installed the gasket incorrectly) it is probably time since you will be in there anyway.
Check your silencer packing and see if it is wet. You can remove just the silencer and feel if it seems like it weighs 10 pounds. If so, its probably full of coolant that is pushed out of the exhaust from the damaged head gasket.