2006 Pontiac Grand Prix Base 6 Cyl 3.8L
Body & Interior
What causes air to blow lukewarm sometimes warm air,but not hot?
No hot air! Has new water pump,thermostat(assuming it was flushed &has new coolant/done a year ago). Temp.gauge needle in car gets to 1/4 point most times. 2day almost 1/2 way,got heat 4bout 10min., then bac 2 lukewarm/ gauge stayed @almost 1/2 way point.
For me, this is what corrected the issue. I was having the exact same issues you are describing. I felt the hoses going to the heater core as suggested on several sites describing this problem. The idea was to feel the heater core hoses if one of them is cooler than the other, then the core has a blockage. They were both hot so I started replacing parts. I replaced blower motor, thermostat and blend door actuator but none of this worked. So, I decided to clear out the heater core anyway. I disconnected both hoses and shot compressed air into the inlet and outlet. I then flushed both the inlet and outlet with water. (Make sure hoses are pointed securely away from you) I repeated this process 3 times. I then reconnected the heater core hoses, took off the radiator cap to clear air bubbles and started the car. After about 5 minutes, the air in the car was hot. After about 20 minutes I put the radiator cap back on and closed the hood. Apparently the heater core was blocked even though both hoses were hot. The heater has worked great now for 3 days and it doesn't take long for it to warm up. Additionally, the temperature gauge fluctuations have stopped. Hope this helps. Good Luck!!