i have a 2002 mitsubishi montero ltd that im having trouble getting heat to work. ive changed the thermostat 3 times with different temp ratings,changed the radiator cap, put cardboard in front,flushed the system 3 times my self and had a mechanic do it 3 times also,ive tried different anti freze 3 times,
now im thinking im down to changing the heater core itself but i have issues with even thinking that this is the problem ,first it doesnt leak in the cab or outside either, second im never low on coolent,third is i can get mediocre heat out of the 2 passenger vents when i press the recirclilating button but i get far cooler air out of the drivers vents, if i switch it to defrost or floor all i get is cool air coming out and since im in minnesota thats not good at all,if it is the core i have no problem having it changed but its a lot of work so if its not then id rather not

 

I just bought a montero with that same problem. I was told there was a valve or something behind the dash that opens it up for more heat, I haven't confirmed this as I will tackle it when I put in my TV/DVD thats when I'll take apart my dash to find that spot. But thats what I have been told is not letting the hotter air out. but when I put it to recirculate the inside air it does get hot.

 

I had just bought a used 2002 Sport also and I am having the same problem. I am getting very hot heat out of the driver side vent and it gets cooler to the right. I had a head that needed attention. Before that work was performed I did not have a problem with my heater. It has not worked since. I had it flushed 3 times and I still have the same problem. Mechanic said it is a clog and with time it will work itself out. Not sure I believe him. It has been 2 months.

 

Did you ever find a solution? Was it the heater core or maybe the relay for the door? I'm having the same issue.