mines beginning to do this. Although it's not as hot as it used to be, it still comes out enough to keep me warm.

 

i have heard of clogged heater cores before. i knwo the cooling system is pretty slimy inside too. if i move the temp control to cold it get ALOT colder. when i have it on heat it just blows slightly warm air. it doens't help much it's been like 20-30 around here lately. i will know next week wne i pull the motor and flush everyhting out