Heater blows warm air (not hot) after running for 1 hr
 

I have a weired issue on my 2008 Elantra. The heater starts blowing luke warm/cold air after running for about 1 hour or so and stays like that. Wondering what might be the problem?

How many miles? Its unusual to have a problem like that on such a new vehicle. It could be that something is telling the "gate" to close off the flow of hot coolant to the heater core after a period of time. On higher mileage vehicles, the likely suspects are a plugged heater core, or a thermostat that is beginning to stick open. Of course, it could be that too.. the T-stat would be easiest thing to replace first.

first question: does the engine heat up fully? i'm guessing t-stat sticking open too.

is it making a clicking sound?