My heat takes forever to get warm. My jeep gets up to temp, according to gauge, in normal time but with it at temp when I turn on heat it blows ice cold. What I have noticed is that when I turn the heat on the jeep seems to dang near over heat so ill shut heat off, then it drops to operating temp and if I turn the heat back on after about 3 mins it starts blowing warm and stays at operating temp. I'm wondering if there is some blockage in my heater core or something. Other than if I try and turn the heat on like mentioned my jeep neve overheats, knock on wood. If I was living back down south wouldn't be that big an issue but these South Dakota mornings are kicking my butt.

 

Are both of the heater core hoses getting hot?

 

Try flushing the heater core by following an online tutorial, and also bypassing the heater control valve if that's something you want to do.

from another thread, about bypassing the valve:
" Go to autozone and buy 3 feet each of 5/8" and 3/4" Goodyear hose, and run them to the heater core lines. 3 feet is actually too long but it gives you enough slack to run down the valve cover and take a couple of sharp turns.

The blend door setup has it so that air blows behind and through the heater core when Heat is selected, and blows in front of the heater core when Cold is selected. So you won't always have hot air but it will be warmer and the A/C will have to work harder"

My valve is bypassed, and it works just fine for me, but I also don't have A/C. Consider also maybe troubleshooting that valve. It doesn't make sense that turning the heat on would start causing your engine to overheat, so maybe consider looking for another issue that's causing this initial overheat.

The easiest way to solve this problem is going to be getting your hands in there and testing what works and what doesn't to make a diagnosis. It sounds like your core is not leaking, which is good news, that is a pain to replace...