I have a 02 grizzly 660 I replaced the water pump with a new 1 and when I try to fill the radiator with coolant it immediately starts leaking out of the over flow tube on the water pump not the weep hole. If I plug the overflow line there it starts to come out by the thermostat overflow. It does this with the bike on or off cold or hot. The top end was recently rebuilt also. Any suggestions? Thanks in advance.