Chevrolet Repair: Chevrolet heater issues, inlet hose, cab pickup

Question
Hello,
My son has a 1999 Chevrolet 1500 regular cab pickup with the 5.3L V-8 engine and automatic transmission. Last week he said the heater wasn't getting as warm as it used to. The truck has 150,000 miles so I figured probably the thermostat was getting weak. Last weekend we replaced the stat and added new antifreeze (dex-cool). We still have the same problem, I was especially careful to be sure all the air was bled out of the cooling system. The engine gets up to operating temp in a reasonable amount of time and stays there. The in cab controls seem to be functioning properly as well (switching between hot/cold, vent/defrost, etc.).
Any advise would be greatly appreciated, thank you.

Answer
Hey,

 Make sure the heater core is getting sufficient flow and that the inlet hose is a little warmer than the outlet.  If the inlet is warm and the outlet is cold you have a restriction to flow or no flow whatsoever.  The blend doors fail all the time on these trucks and are located in the HVAC box.


Wayne


If dex cool is changed before its 5 year interval it will not plug up a heater core.  Gelling only happens when you mix coolants or neglect the coolants age and ph

w