Is it overheating, or normal operating temperature and just dumping coolant on shutdown? Most importantly, how far are you filling the radiator? DO NOT top it off. A radiator with just a coolant overflow hose, and not a coolant recovery system, only gets filled to the top of the core, or about 1"-1 1/2" below the filler at the most. Overfilling the radiator is just guaranteeing that it will puke coolant every time you shut down.
