water problems after fitting fmic
 

i have a 2002 sti, just fitted a front mount but u have to change coolent tank for the 1 suplied,(never touched any rad or water pipes just 1 that slot strait in to coolent tank) once fitted i started the car and it started throwing water back into the coolent tank i wasnt sure this was right or not, i took it for a test run and it blew the cap of the coolent tank were it was over flowing and wen cheacked the header it was empty, i dont no why its doin this as it was fine b4 i changed tanks,it never lost water in any way b4, both tanks were spot on wen cheacked it dont over heat or anything, any 1 got any ideas or have had the same issue???? cheers