Suddenly no heat - thermostat?

[grandmarq]

Just had the oil changed - and realized no heat the next day (yesterday). Car is running a little weird...sounds a bit like a diesel truck if I step into it a bit.

I replaced the thermostat, but the heat has not restored...
When idling, the gauge eventually rises...approaching the red line...but doesn't quite get there. Of course, I turn it off before.

The thermostat instruction stresses correct replacement, bur it's so straight forward, I can't imagine I put it in wrong. I did have to add fluid to the reservoir after putting it in...and I have the front end up higher to burp the system...

heater still doesn't blow hot...I suspect the diesel truck sound will ensue if I try to drive away....any ideas??