05 buick lacross with no heat changed the themostat?

The thermostat problem is spotted by an overheated or under heated engine.
The reason you are getting no heat is the valve to the heater core is bad, or the core itself or one of the hoses is bad. I have an 05 lacrosse with the same problem. I can hear the water circulating in the core which seems to fluctuate in volume and is related to the heat output. I tried to increase and decrease the temp to see if that would unstick it. I am pretty sure I have a blockage in the core itself. If need be I will go to the junkyard and rip one out for 20 bucks and replace it.

If you are going to buy any parts online I setup a page that links to auto stores. It's the same stores, but by clicking thru my portal you get cash back, I make a small percentage, and you pay the same price or less than if you went to the site itself. I still haven't figured this one out, but it works. http://tinyurl.com/ya23vt6