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Poor Heat - 2007 Grand Prix GT

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On my 2007 GP in the past I've done the following:

 

 - New T-Stat.  195*F which is stock.

 - Bled cooling system with one of these:  https://www.amazon.com/EPAuto-Radiator-Coolant-Filling-Funnel/dp/B01I40ZQWE/ref=sr_1_2?ie=UTF8&qid=1508244770&sr=8-2&keywords=radiator+funnel+bleed

 - Checked/re-checked coolant levels.

 

My issue is this:  the car gets up to temperature just fine.  Once the T-Stat opens and I'm traveling at highway speeds (55mph or so) the temp on the gauge and inside the vehicle drops.  It isn't cold per say but it's chilly enough that my windshield won't get fully cleaned off.  My past W's were always HOT in the winter and this is lukewarm at best.  During the summer the temps get to the middle mark and stay there even in extreme heat it rarely moves above the middle.  Now I'm lucky to be on the first hash.  (there are 4 bigs lines on the 04+ so I use the middle one as 'where it should be')

 

This car doesn't have the metal cap so I'm thinking maybe replace that next. 

 

The only things done to the car are intake and I've removed the engine cover.

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I bled it twice last winter to be sure.  Never did replace the coolant.  Color was good at that time I was closer to 53k miles. 

 

I have a feeling the backflush is what it needs.  Tstat was a good one but I'd do it anyway.  Might just do a full flush, backfill and see what it does.

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Same issue here, Mine was fine until I flushed everything twice, I have a feeling I got a bad thermostat I didn't notice the heat thing until last night, but mine acts like it has some air until I rev it a bit which seems to open it until next cycle

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On my 2007 GP in the past I've done the following:

 

 - New T-Stat.  195*F which is stock.

 - Bled cooling system with one of these:  https://www.amazon.com/EPAuto-Radiator-Coolant-Filling-Funnel/dp/B01I40ZQWE/ref=sr_1_2?ie=UTF8&qid=1508244770&sr=8-2&keywords=radiator+funnel+bleed

 - Checked/re-checked coolant levels.

 

My issue is this:  the car gets up to temperature just fine.  Once the T-Stat opens and I'm traveling at highway speeds (55mph or so) the temp on the gauge and inside the vehicle drops.  It isn't cold per say but it's chilly enough that my windshield won't get fully cleaned off.  My past W's were always HOT in the winter and this is lukewarm at best.  During the summer the temps get to the middle mark and stay there even in extreme heat it rarely moves above the middle.  Now I'm lucky to be on the first hash.  (there are 4 bigs lines on the 04+ so I use the middle one as 'where it should be')

Backflush doesn't fix an engine that isn't warm enough.  Backflush may improve coolant flow through the heater core or the radiator.

 

Your engine isn't staying warm.  Faulty thermostat.  Are the cooling fans running?

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Drops almost 1/4.  Gauge is at half when the car is "hot".  When the t-stat opens (i'm assuming) it drops to nearly 1/4.  Thinking I should flush the system and do another new t-stat. 

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Can't say it warms after sitting but it will warm up if I hammer on it.

 

Gonna do another t Stat and bleed the system down again. Havent had much time to check it out but it hasn't been cold either.

 

 

Sent from my Pixel XL using Tapatalk

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Air in the system maybe? Had the same issues when I replaced my radiator last year. Finally I bled the air out with the bleeder screws and that solved my issues. Good luck man!

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It helped marginally, but at this point I'm thinking my heater core is blocked up. I flushed everything up good in the spring, but I didn't do the heater core on its own so that's probably the issue now

Could maybe your blend door be stuck, or not working. Maybe the heater control valve?

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Could maybe your blend door be stuck, or not working. Maybe the heater control valve?

You reminded me of an issue I had on my '95 Cutlass that could apply here...I had a failed actuator that operated those doors on my old Cutlass, though mine failed open, which meant I had heat 100% of the time.

 

Mine had the electronic climate control, so it had actuators, rather than using cables or vacuum to operate the doors.  I honestly don't know what method is used on the 2007's...but if I were a betting man, I wouldn't be surprised if it uses actuators, too.

 

I about died when I saw what new ones cost---nearly $250.00.  After some patient searching, I found out that certain full sized GM pickup trucks used a different part number, but it was compatible.  Found one in a junkyard, on a truck that someone had already removed the dash--cost me $5.00, and about 5 minutes of work removing it---and nearly 2 hours to properly install it on my Cutlass.

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