help! coolant probs

[rubin110]

hi guys,

i have a 2000 x5 4.4i and it had an upper radiator hose leak. fixed that and then it started leaking from a pinhole in the expansion tank, replaced that and now its leaking right out of the cap! its like the system cant handle the pressure. earlier today after driving for about 45 min, it sounded like the antifreeze was boiling and it was coming out of the cap. i spoke with my mechanic, he said i need to bleed the system. i am going to attempt to bleed the system once the truck cools off. i have read some posts about the thermostat. does it sound like i might have thermostat troubles? if so where is the therm and does anyone have instructions on how to replace it?

Thanks guys!!!!