Mitsubishi Repair: 95 Galant heater blows luke-warm air, chrysler plymouth, radiator cap

Question
I was a mechanic for Chrysler/Plymouth for several years (but that was 25 years ago). Now I own a '95 Galant and winter is coming,,,but the heater blows only luke-warm air. I've replaced the thermostat and flushed the system. Feeling the heater hoses as they go into the firewall, one hose is very hot while the other is cool to the touch. Does this car have a heater-valve that could be blocked? Or is the waterpump failing and not pushing the coolant volume enough. OR could there be 2 thermostats on this vehicle (I think it's the 2.0 motor). Thanks  

Answer
Ken:Surely you have a repair manual for your car. It will give you all kinds of ideas to check. But I would check the drivebelt tension and waterpump.But your heater core could be weak or going. How about the fan that blows the air through the heater, is it maybe not blowing enough air. Look I try to find the easy and less costly things to check first. Then go to the more costly things. How good is your radiator cap, there has to be good pressure in the system for the water to move with the waterpump. Are you sure the heater switch is working as it should, going from low all the way to high? Or could it be stuck at a cooler air flow temp? When you start the car can you hear what sounds like water boiling in the heater area? If so then it is most likely your heat core. Hope this helps and good luck!