I have the 4.0 liter I6 engine. My thermostat is working correctly, the hoses going in and out of the heater core are both hot after the engine gets up to temperature, but i only get moderatly warm air when I turn the temperature control all the way hot and fan to 4. This is in 70 degree weather. When it gets cold it still blows moderately warm air but nowhere near hot enough to heat the car.
As far as I can see it is one of three things.
1.) Actuator isn't letting enough coolant into heater core.
2.) Heater core is plugged.
3.) Blend door or motor is malfunctioning.

I want to say it isn't 1 or 2 because both hoses get hot. So that leaves me with a blend door issue which i will be looking at soon. Does anyone else have ideas on what could be wrong? How exactly does the actuator work on this model? Thanks.

 

First off, you have an I-6, not a "V" motor, and you are on the right track, as it could be any of the things you listed. As for the blend door actuator, I'm not familiar with HO XJs, so I can't help too much there. Best of luck!!