[cardoc]

I know this seems menial but did you fill and vent with the cap off when you first replaced the coolant? I usually let the engine come up to temp so the thermostat can open to verify all of the fluid is circulating through the block. With the cap off you'll know when it opens and sucks down from what is in the radiator.

Plus, it lets the air out.

When you replaced the thermostat, was there coolant in the radiator?