What kind of water pump was installed? Just because it's new doesn't rule it out. I put in a new Bosch water pump last spring that went to crap in December. The plastic impeller cracked and it was loose on the shaft. It would do ok around town but would begin to overheat within a few miles of highway driving.
Not sure if thats your case though with the cool hose on the bottom, but definitly something to keep in mind if it has a Bosch waterpump.