overheating
 

Just start the car after several month and the water flush out...Could be the water pump get stucked? The electric fan starts to blow when water gets out, so the thermostat is working...
Also the upper water hose seems to "breath"/pump, like some pressure builds up there...

Thanks!:surr:

Are we talking about the car in your avatar...an '8X 924?

We understand that English is not your primary language...but please try to describe your issue in greater detail. When does the coolant overflow...after driving for hours, or simply after idling in the driveway for 5 min?

Without more details, it sounds like the cooling system could be getting pressurized by combustion gases due to a failing head gasket.

My 87 924S stay parked for 4 years now... I only start the car for 10 minutes every two weeks, and drive it 30 meters...
When last time start the car, the coolant overflow from the coolant reservoir cap. No steam, no bubbles, no oil on water, no nothing.

In that case, suggest you replace the reservoir cap [with an OEM part].

I don't think the thermostat has anything to do with the fans coming on. you may have a bad thermostat, check the hoses to see if they heat up past the thermostat.