The temp gauge goes to the HOT side after a short ride even though the flex fan is turning. When you feel the top hose it's cool at times when it shoud be HOT which says the thermostat isn't opening up soon enough. I just bought a T stat, but what would cause the top hose to collapse on itself shortly after the engine is shut off.

 

Hi,
You said you just bought a Thermostat,does this mean its installed,and the hose still collapses? or are you just inquiring as to what could cause the problem before replacing it?
This may sound like a dumb question,but my first suggestion would be indeed thermostat....