2500hd thermostat

[motorsports12]

I had a radiator leak and while I had it tore down I figured go ahead and change the thermostat ... A bolt broke so I ended up tearing it all the way down removing the water pump ... water pump, new hoses, new thermostat, new radiator ... after getting it all back together and filling with new antifreeze I fired it up let it idle ... heat on high ... reved it to 2500 rmps a couple of times ... let it idle... the gauge went to 210 but it always ran at 210 (thermostat is a 187) ... heres my issue ... upper radiator hose gets real hot but the bottom hose never did while it was running ... Im getting great heat out of the vents ... I shut it off and ate dinner went back out no change upper hose hot bottom still cool ... go through the whole thing again ... heat on, rev to 2500 rpm a couple of times, good heat through the vents, gauge is at 210 ... the hose are still the same ... it like the thermostat isnt opening ... then I clean up all my tools and the garage (bout an hour and a half) and check the hoses and now the bottom hose is the same temperature as the top hose ... did the thermostat open? did I get all the air out of the system? is the thermostat bad? I really dont want to tear it all down again ... any help would be appreciated

[motorsports12]

2012 GMC 2500HD WT with the 6.0 flex engine

[Stealthee]

Sounds like you had an air pocket. Sometimes they are just stubborn.