Heater Doesn't Heat! Help!
 

So my heater just started to not work ... could this be an open thermostat or the heater core? I checked the coolant levels and they are fine. Is there a way to figure out what it is without replacing the heater core right away, because honestly, I'm not sure how to do that?

Thanks!

When you say it doesn't work do you mean it doesn't blow or it doesn't get hot? Also was it like working yesterday but not today or what exactly happened? Little more details could help. But for now I would say it could be a stuck open thermostat or a clogged heater core which you could try flushing yourself at home.

My apologies for the hasty post. It blows air, but LESS forcefully than it did a year ago. The temp of the air is also much lower than it was. The temp doesn't climb to much more than what it is outside. It may have been a gradual process, but I've only really noticed it in recent weeks.

So in essence, it is working less all around.

I would try flushing the heater core with a garden hose before anything. Just pull the hoses off the firewall and alternately let the full blast of the garden hose clean out the heater core. Just go back and forth to each of the holes on the firewall until clean water comes out.

The hoses inside the car or in the engine bay?

Engine bay. You will see the 2 heater hoses going into the firewall. Pull the clamps and hoses off and just put the garden hose against it to get a good seal and just let er rip. The order I personally go in is to pull the heater hoses, put garden hose on full blast, kink garden hose so I can line up the hose with the firewall, and just kink and un-kink as needed to go back and forth between heater core.

They wouldn't be the two small hoses coming off the water pump would they?

i couldn't honestly answer that until I went and checked my brother's LS1 TA out back. I have an LT1 and the pumps are different. I know for a fact though if you look at the firewall you will see 2 heater hoses going to it. Just pull them off there or follow them back to the pump and see which lines they are.

There's a diverter blade that directs flow around or through the heater core. It sounds like it's not directing the air properly.

Yes those two hoses would be it. Oh and FYI as soon as you take off those hoses coolant will start pouring out of there for a bit.

use a couple of vise grips to pinch off the hoses(heater core) side so you dont loose coolant out of you block,you still will loose whatever is in the heater core but that is not a big deal just check the overflow when your vehicle has reached its operating temp.

Is your car reaching operating temp? If not, I would address that first, but if so, I would move past the thermostat.

As far as the heater core; in the past, we checked for a plugged or poor flowing heater core by feeling the temp of the two heater hoses as the engine reaches operating temp. With the heater temp turned all the way up, and the blower on low, feel to see if both hoses are similar in temp. If one is cold, you are not getting proper flow. If this is the case, I would drain the whole system and "backflush" the heater core as previously mentioned. One trick we used to use was to put a small amount of Lime Away in the radiator and drive the car for a little while (a day or two) before performing the drain and flush. This can loosen up corrosion and calcium deposits. (I would not drive it this way to long, I don't know what effects this might have on other components.)

As long as you are performing the drain and flush, take advantage of this time to replace the thermostat.