2001 disco II, was driving the the other night when the heater started to blow cold air..soon thereafter the temp gauge started to rise steadily..found coolant reservoir low..filled it, fan seems to be operating smoothly..what could be causing the heater to blow cold air?

 

your heat is provided by the warm engine coolant running through a "radiator" ( HEATER CORE) in the dash , the fan blowing cold air means that there is too low a coolant level for the coolant to flow through it. Most likely you have a coolant leak somewhere and that needs to be found before you ruin the engine by overheating it. check out the D2 coolant bleeding procedure in the how to section of this forum..........do that first to get things right....and then start looking for the leak.