Well my heat in my jeep will not get hot it will get barely warm. I have replaced the t-stat. And with winter approaching I would like to know how to fix the issue.

 

Have a buddy work the heater lever, while watching the heat bypass valve under the hood. (Opening or closing) I'm guessing it isn't closing. Shut manually, see if heat comes out. The valves are known to fail. Or possible clog in heater core? JMO!