96 Cavalier 2.2 thermostat question

Me and my buddy replaced the head gasket on his 96 Cavalier, along with all new other gaskets and a ew thermostat. Now here's the problem. The car starts, idles fine, no leaks. We bled the cooling system a few times. Took it out for a spin for half an hour or so, came back to the garage to check on things and the lower radiator hose is COLD (where the thermostat sits). The temperature gauge reads normal (the needle is right in the middle of C and H). The car blows heat very well from all vents. But why is the lower radiator hose cold? That means that the thermostat isn't opening and it should be, correct? The upper hose is nice and hot. The new thermostat is a 180F Duralast from Autozone so i know it's not exactly the best one out there. Any ideas or suggestions? The car drives great, no leaks, temperature is perfect and it blows hot air...

This always happens with Duralast and pretty much any other thermostat that's not OEM specific, happened with my 96 2.2 and alot of others, it's just the thermo, no biggie. It kinda was for me tho, when it did on mine it threw the Check Engine on and I couldn't get my car inspected with that on so I could sell it, kinda sucked but it eventually went away.