Hey guys, my 02 KJ is having a heat problem. I start her up, let it warm up, and when I go to turn on the heat, the heat only stays hot for about thirty seconds. It really *****. Brought it to my mechanic and we checked the coolant levels, everything was normal. His guess was that there could be a clog or that I need a flush. I'm not to car savy, does this sound right? Or any ideas? Thanks for the help