I have a BX that is two years old with 150 hours on it. According to the manual the coolant should be changed every two years. The manual said open either the radiator drain plug or the engine block. It said nothing about opening both. I opened the engine block because the radiator drain plus was difficult to access and I figured the block was lower. Unfortunately, only about 1.5 quarts (or half) of the coolant came out, maybe about another half of quart from the overflow tank that I removed with a syphon. So do I need to drain the radiator too? If so it seems easier just to remove the hose. I actually added 1.5 quarts of new coolant since I needed to move the machine for the night. Do you think this job is good enough to call it done for the next year or should I redrain the entire system?