2005 Chevy cobalt collapsed upper radiator coolant hose

I have a 05 Cobalt with 40,000 miles. One nite after i got back from a business trip i was driveing home and my check engine light come on. So i went to advance auto they hooked it up to there scaner and came back with p0128. AKA coolent temp low the thermostat was stuck open. So i took the car to the dealer see if i can get it replace under extended warranty. well they would not because they said its a wearable part. They said to fix it  it would coast me $450. well i dont have $450 so i took to a friend that works for gm and i told him ill give him 200 to fix this. (he has worked on my cars befor and has done great work).
 
So after he get all the work done and the car was runing at 189 to 192F. then  I seen that the upper radiator coolant hose was collapsed. I freaked out i never seen that befor. he told me it was nothing. I dont think its nothing after i played with the hose and forced it to open it seem like it was staying open. then he added more water in the  over flow and it sucked it down and stayed open. well we drove home every thing was alright the car was runing great. well later I went over to my friends house and when I was about to leave i thot i should check the hose and coolent lev in the over fllow. well the coolent lev was fine but the hose was collapsed agian but the temp of the car was at 189 to 194F. the hose is collapsed when the car is off and when the car is on.  
 
Please help me out why is my coolent hose collapsed?? Please email me at rlucci06@hotmail.com if you have any idea it would be greatly appreciated. Thanks Riley

if u have air pockets in ur coolant system that can cause ur hose to collapse. or if u have a bad radiator hose.