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2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
12-28-2011, 02:20 PM
Post: #1
2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.

Problem: Very little heat inside the vehicle, brought it to a GM dealer and had the coollant system and heater core flushed out. Dealer mentioned that there was debris in the heater core that required additional flushing of the core before it was cleared. Dealer replaced the thermostat which was faulty and replaced coolant. After this there was a slight increase in heat but not like before. Fan control switch inside the car only cuts in from the 12 o'clock position to full speed, not sure if this is the cause. I checked and the heater hoses on the firewall are both hot after the car warms up. Can hear the motor for the temperature control working when moving from cold temperature setting to hot temperature setting. I did notice that on cold days if the fan control in the vehicle is off then the thermostat gauge moves to the midway point on the gauge dial but when the fan is turned to the full speed then the needle of the gauge drops back to the 1/4 dial setting.

Any idea of a cause of this problem? Could it be caused by the blend door issue or is it the heater core. Any advice on a possible cause of the low heat problem. I did not want to replace the heater core unless this is definitely the cause of the problem.
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12-28-2011, 02:34 PM
Post: #2
RE: 2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
Sounds like you may have more than a single problem and at only 4 years old I find it hard to believe the core was clogged up.

What I would do is double check that the system is COMPLETELY full and go from there. The fact that the temp gauge doesn't go up all the way might be an indication of either the wrong t-stat or one that is faulty.... or the cold amibent temp you speak of is in the single digits, which may not allow the engine to reach full temp.

On the blend door issue, if it's working and you are getting coolant flow with some heat in the cabin then you should feel a difference between the in / out hoses temp wise. OTOH, if the system is not totally full then there could be intermittent air trapped in the core, which will lower the heat output.

One other thing I have seen on some GM products is a bad water valve. When they fall apart internally they restrict the flow. I do not know off hand if this car has one. The easiest way to find out is to ask at the parts counter. If it has one then they will show a listing for it and likely a picture of where it's located.

Let us know how you make out.
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12-29-2011, 10:28 AM (This post was last modified: 12-29-2011 10:34 AM by agwilli.)
Post: #3
RE: 2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
The engine (3.8 L, V6 with A/C) as 150000 kilometres in it and is running excellent. When I got the car back from the dealer I checked the coolant level when the vehicle was running figuring that the fluid level maybe low or air locked but the coolant level was good. I will recheck this again today.

Yesterday while driving home the temperature gauge only reached the midway point between the 1/4 mark and 1/2 mark on the gauge. I also moved the temperature control inside the car from cold to hot and then back several times, and I could definitely feel a difference in the cold and warm air flow. As you say, it is possible that it's still an issue with the thermostat which would not allow the engine to reach full temperature.

You figure maybe there is still air trapped in the coolant system and heater core - is there any way to bled the air form the collant system? I know the dealer mentioned that had trouble bleeding the system which they noted on there work order, so this still could be an issue.

I'll also check to see if the car has a water valve.

Regards
By the way, I checked with the dealer and the 3.8 L, V6 engine does not have a water valve, They mentioned that older engines did have a vacuum controlled water valve but the 2007 Grand Prix does not.
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12-30-2011, 01:15 AM
Post: #4
RE: 2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
Bleeding the air from the system can be a real pain. The first thing to do is look for a bleeder valve on the engine usually on or near the thermostat housing. Some also just have a small, pipe thread plug. If neither of those are available the next trick is to get the front of the car up in the air. Pull the front end up a steep incline, up on ramps, or jack it up. Whatever method you use, do it safely. Block the wheels to prevent rolling or use jack stands to prevent it from falling. Once up in the air; with the engine cool, remove the radiator cap, start the engine, & allow it to warm up. As it warms the coolant will keep "Burping" air bubbles. As the air is purged you will need to keep topping up the coolant. You should also put a "catch" container under the vehicle as some coolant will overflow.

Hope that helps. Please keep us posted.

Thanks for using the forum,
Garner

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01-10-2012, 01:14 PM
Post: #5
RE: 2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
Update, container of radiator flush did the trick and cleaned out the heater core. Car again has full heat inside just like when it was new. Thanks for the assistance.
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01-10-2012, 09:57 PM (This post was last modified: 01-10-2012 09:59 PM by Rupe.)
Post: #6
RE: 2007 Pontiac Grand Prix, 3.8 L V6 with AC - low heat inside vehicle.
Thanks for the up date and glad it was a simple fix.

Most of the time we presume the simple things have been done already.
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