4.4i heater issues

[x5Alpine]

my 2003 x5 4.4i has had an issue where when I turn the heater on it'll blow hot air from both driver's and passenger's vents but after around 5 minutes the passenger's side starts blowing cold air. Tonight I replaced the water valve with a brand new OEM part but the issue still persists. Any ideas would be appreciated.

Thanks!

[AussieXer]

I’d check the coolant level carefully and get it at least on the correct range. Mine has a funny float that sticks up above the mouth of the filling tube. Check the level again after a run to operating temperature. May have to make sure the system has no air in it (bleed it). Thermostat is another possibility. Not a difficult replacement. Dual zone temperature control so may be a good idea to feel the hose into the heater solenoid and both the outlet hoses.

[andrewwynn]

My NT510 will show the state of each and every part of the heater system so temp of each heater core and each flap motor as well as the Realtime state of the heater valves. I recommend a good scanner so you can track down problems like that.