No heat from my '04!

Driving to work this morning, I noticed that my Impala was not pumping out any heat. Of course it had to be only like 13 degrees. Anyhow, engine temp was normal. What/how should I check 1st? I am needing to take this car on a long drive tomorrow. Just my luck. I do not think it is heater core as I do not smell any hint of coolant inside the car. Any quick help with some diagnostics would be great!

2004 LS 3.8

Your heater core could be blocked, or done. I'd definetly try flushing it out before replacing it.

It could also be the vent or valve which changes the air from hot to cold.Did you turn it down and then back up .I think they are controlled by vacuum.(just a possibility)

Hey Fellas,

Thanks for the responses! I did have to take it in to the dealer to get it checked out as I was short on time with having to go out of town. Sure enough, after the dealer had the car for 5 hours, they figured out that there was either an air bubble stuck in the heater core or sediment build up. Either case, after a good back flushing the heater was once again kicking out a hot 140 degrees.

air bubble stuck in the heater core or sediment build up
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what could cause this? seems not usual

If I had to guess, it was one of two things;
When I checked the overflow tank, it wasn't empty but it was low. I think that the system was sucking air. I also noticed that the overflow's cap was off possible sucking in dust through the system.
I guess I will have to keep an eye on the level of the overflow though I though there would be a light on the message center telling me that I had low coolant.
Thanks for the responses!