bubbling out of the resevoir sounds like a broken over-flow tank cap. Mine was replaced 3 times in 6 years. These damned plastic caps get hot and crack (sometimes underneath where it is hard to see from above). Well, my 2 cents worth. The whole system is under pressure and that's normal (don't know about the fan running after...seems mine didn't) so if the pressure is released by a leak in the system (like a cracked cap or bad seal) then of course it is going to sizzle out. Is your engine temp up more than normal?