Poor heater in 1998 dodge 1500 ext cab 4X4, blows Luke warm air.

If someone has removed the thermostat the engine will run much colder providing less heat to the heater core. See if the gauge on the dash shows normal temperature. If it is low, check it. Is the heater fan blowing at full speed? There is a device on the heater core under the hood on the passenger side that controls the fan speed. I have seen them burn out. They are easy to replace and not expensive. Is the ducting under the dash complete and connected? I once knew a guy that put a new radio in his dodge and ripped out the ductwork to make it fit. LOL Come wintertime he had no heat either. Also MICE may have set up a home in your ductwork blocking the airflow. You may have a partial coolant blockage in your heater core. Rust, gunk, etc. Remove both heater hoses from the heater core under the hood and try to run water through it from your garden hose. That might flush it out but don't be too aggressive or you could blow out the heater core. It is designed to handle 15 to 20 psi and your garden hose could have 40 - 50 psi. Be careful. They also have radiator "flush" kits that might un-block a partially plugged core. The water pump could be failing, not providing enough coolant flow. Look at it and see if there is coolant leaking around the pulley or the "seep" hole on top. Replace if there is. Hope this helps. Good Luck

Also could be a missing or cracked vacuum hose that controls the amount of coolant flowing to the heater core. I had a broken heater valve one time and just blocked off the vacuum hose and turned the valve to "on" for the winter..... It is very obviously connected between the engine and the heater core on one of the hoses.

i own one,../ a 1999 dodge 2500 , cumin's diesel.. here is the deal..: the heater cores are higher then the engine , the in and out lines to the heater core.. run up hill..!! so if the heater core drains , it gets a " Air pocket" stuck in the heater core that's a booger to get out..!!! my story ..: i changed out a thermostat that was sticking , and all of a sudden my heater only blew look warm air,..??? all you need to do is,..just BLEED the Air out..:) , / a high angle/ with the heater open engine running $ warmed up,.. mite do it.., i finly put in a " T" the out line ( of the heater core) and a bleeder valve in the "T".. above the heater core line.., bleeder above the heater core,.. then bleed it , if this save you from pulling a dash and heater core,,? ..say thanks.. ..:)