Hello and welcome.
Are the bubbles and no heat the reason you replaced t-stat, or is this just happening afterwards?
The reason i asked is that this engine is common for headgasket problems causing air pockets in the cooling system- so no heat. The rear headgasket is most prone to this. You should not have to replace a t-stat every year. I would suggest pressure testing system, or looking at passenger side of rear head for signs of leaking. Inspecting spark plug would also show a problem with a headgasket.
Other than that, best way to get air out after a cooling system repair is to have engine off, loosen the bleeder and let air purge until only coolant coming out. The bleeder is on top of a pipe, above the water pump area at passeenger side of front valve cover.
Then close bleeder. Let run until hot, shut it off, lossen bleader again to let out any remaining air. May take a few times.
If it persists, i would definately look into a headgasket problem. Especially if it is boiling over.
Yes, sounds like air in the system.
Would look into headgasket problem.
Air pockets in the system around the temp sensor will not show proper coolant temp. Sensor cant read air, only fluid.
As described above, use that bleeder screw.
Then cap it off and take it on a short drive. Do a few hard accelerations, and the this will usually get it out. You will notice all of a sudden blows nice and hot.