poor heat while at idle?

2009 PONTIAC TORRENT
160,000 MILES • 3.6L • 6 CYL • 4WD • AUTOMATIC
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KEN BRUCE
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  • 1 POST
Poor heat in cab when at idle. Keep revved to 2500rpm and improves significantly.
Feb 5, 2026 at 12:14 PM
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STRAILER
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 54,176 POSTS
I would wait until the engine is cold and then check the coolant level, it sounds like it is low. If the level is okay, I would remove the heater hoses and use a garden hose to flush the heater core out, this should fix the problem. Here is a video to watch which will help you fix it as well.

https://www.youtube.com/watch?v=SNRb6pSwYuU

Please upload a short video in your response of the problem, so I can see what's going on.
Feb 6, 2026 at 7:56 AM
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KEN BRUCE
  • MEMBER
  • 1 POST
I have flushed and reversed flushed the heater core, also with CLR and short bursts of air. Bled system and bled some more, and could get no more air. Replace coolant thermostat and installed new water pump. Still it loose 80% of heat immediately at idle.
Feb 12, 2026 at 9:23 AM
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STRAILER
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 54,176 POSTS
You might have low coolant flow to the core, when the engine is hot and the heater on can you feel both heater hoses to see if they are hot as well? Also, I would check the temperature blend door actuator to make sure it is working correctly. Check out the images (below). Let us know how it goes
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Feb 12, 2026 at 9:27 AM