Correct 👍🏼 I'm aware that it should have already been changed lol

 

A stuck open thermostat! Cold air will blow from the vents!

 

What am I missing? How can it blow cold air if the coolant is at 180*?

 

The may not necessarily mean "cold" they might mean "not hot" if that makes sense. On my LT when the temp just barely turns over to 180 it isn't quite as hot as it is when the temp gets to 190. At 180 the thermostat is designed to start to gradually open, thus the heat may be different through the vents until the engine and coolant system reach true operating temp. Just my 2 cents LOL. Also, even for an LT I think running down the road after a good ways at only 180 is too low. On nice stretches of highway my temp sometimes can get down to 183 but thats about it. I dont thing the computer will trip a code until the temp drops to 176 or below for a certain period of time.

 

Thermostat is open the coolant won't get hot as it constantly circulates, it's not in the block long enough to rise to temperature. Now this should trip a code, P0128, but I have seen HHR's with this issue and not set the code.
I've changed the thermostat and flushed and filled the Dexcool and then there was heat.
I don't know the physics of it I just know the results of it!

 

You can use some air to check for obstructed heater core while the t-stat is out.

 

Ok so here is the latest.....left home, hopped on the freeway. The heater was already warm at 180. It was warm until half way to work and it just flat lined and was like warm. At that time, it was sitting anywhere between 190 to 200 still blowing luck warm. I'm assuming the thermostat is stuck open.

 

And or there is air in the heater core, but because of age , replace the thermostat and the Dexcool.
Park the SS nose up a sloop like a driveway or jack up the right front corner to allow the air to escape, put the heater in full heat while your refilling the rad.

 

Well, when you're at 180 or above, it's supposed to be open. Being 'stuck open' should only be a problem for getting to operating temp(and would set the P0128 code). Once you reach operating temp, it's supposed to be open. That's why I don't think it's the cause of your heater not working properly.

I would be looking for a clogged heater core(like donbrew suggested) or a blend door problem(like firemangeorge suggested).

But sure, you're probably due to replace the thermostat and the DexCool, and like donbrew said, blow out the heater core while you have the thermostat out.

 

IF it turns into a blend door actuator issue, here is a link to the procedure. Thanks to former mod ChevyMgr.
Post #11 in this link: https://www.chevyhhr.net/forums/prob...m-33767/page2/