Out of no where my 944 is spitting its coolant back out of the expansion tank through the overflow hose. I can't figure out why, I'm thinking it could be the tank's cap (which has never given me any problems) or the thermostat (which has never given me problems either). The odd part is I can't figure out the timing in which the tank wants to overflow; never after long drives, but shorter drives. I'm thinking that once I turn the car off the cap isn't releasing the pressure, so when I start driving it's adding pressure to whatever pressure was added prior. Any ideas?