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Discussion Starter · #1 ·
I have a 2007 G6 GT Convertible Coupe (3.9l V6), and the coolant (no matter how many times I refill it) is always low. I can’t find a leak, and now the heat doesn’t work unless the vehicle is moving. I’m not sure if it’s the thermostat, if there’s a leak I’m missing, or if there’s just a small air pocket somewhere in the coolant lines. All I know, is that the heat works when the car’s moving, and it doesn’t when it’s stopped. It’s bad enough that I’ve spent more on coolant than I have on gasoline, so I’m guessing there’s a leak. I just need a helping hand. Anything would be much appreciated.
 

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I've got a 3.9 LUCERNE that was always losing coolant, Found that the spring type lower radiator hose clamp at the radiator was broken and allowing slow leak when not being run. The fan shroud blocked being able to see the source of the leak, along with how it was mounted in the car. Low coolant before refilling the res. will give air pockets in the motor/coolant lines, and probably why you only get heat while moving. Check all hose clamps, no matter how hard it is to get to them. I fought to get the 2 pieces of broken spring clamp off for a couple hours on my Lucerne and then used a screw type hose clamp. NO MORE LEAK and constant heat when wanted.
Good luck!
 

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Discussion Starter · #3 ·
I've got a 3.9 LUCERNE that was always losing coolant, Found that the spring type lower radiator hose clamp at the radiator was broken and allowing slow leak when not being run. The fan shroud blocked being able to see the source of the leak, along with how it was mounted in the car. Low coolant before refilling the res. will give air pockets in the motor/coolant lines, and probably why you only get heat while moving. Check all hose clamps, no matter how hard it is to get to them. I fought to get the 2 pieces of broken spring clamp off for a couple hours on my Lucerne and then used a screw type hose clamp. NO MORE LEAK and constant heat when wanted.
Good luck!
I will definitely give that a shot. If it doesn’t work, I’ll be sure to let you know. Thank you so much.
 

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One of the most common G6 coolant leaks is a cracked "T" piece on the hoses below the coolant reservoir. In some instances, you may see fluid near the transmission selector. Another issue on mine was the plastic riser on the front left of the engine (it has a metal tube coming out of it). I tried replacing mine but there was still some steam coming off when the engine was hot. I ended up adding some gasket seal on the bottom where it bolts to the engine block and this did the trick for me. Using a flashlight at night when the engine is hot made it easier to spot these leaks

For the heat / moving side of the question, are you sure the HVAC fan is running? If not, you would only get airflow when the car is in motion. Just a thought. Hope you find and fix it.
 

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Discussion Starter · #5 ·
One of the most common G6 coolant leaks is a cracked "T" piece on the hoses below the coolant reservoir. In some instances, you may see fluid near the transmission selector. Another issue on mine was the plastic riser on the front left of the engine (it has a metal tube coming out of it). I tried replacing mine but there was still some steam coming off when the engine was hot. I ended up adding some gasket seal on the bottom where it bolts to the engine block and this did the trick for me. Using a flashlight at night when the engine is hot made it easier to spot these leaks

For the heat / moving side of the question, are you sure the HVAC fan is running? If not, you would only get airflow when the car is in motion. Just a thought. Hope you find and fix it.
My HVAC fan is working; it just blows cold air when I’m idle at a red light/stop sign, etc., and it switches from hot to cold almost immediately. I added more coolant to the reservoir (the only thing I hate about this car is the fact that there’s no radiator cap), waited for it to drain into the rest of the system, and then filled it up the rest of the way to the fill line. It works fine for now; going to check it again in the morning before starting my vehicle. I have a sheet of cardboard lying underneath the engine compartment, so if it’s leaking, I can attempt to get a general location of the leak before starting the vehicle.
On a side note, my reservoir fills back up when I remove the cap, so I’m guessing there’s some sort of fluid lock (similar to a vacuum) inside the coolant lines. It’s just strange to me. May not be anything to worry about though; just figured I’d mention it since I noticed it a bit earlier on in the day. I do appreciate all the encouraging words and well wishes. The same goes to you all.
 

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2007 G6 GT conv
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Hi...Hope you have success...My issue end up being the gasket between the input manifold and the heads. very difficult to track down. It took two times to my mechanic shop but they nailed it and the was 5-6 years ago. With the second gasket they even put an additive in the radiator fluid to eliminate the chemical reaction on the gasket and material which had eaten away the gasket, hence the leak. That was the second gasket when they figured that part out. The first replacement gasket did not last a year.
 

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I have a 2007 G6 GT Convertible Coupe (3.9l V6), and the coolant (no matter how many times I refill it) is always low. I can’t find a leak, and now the heat doesn’t work unless the vehicle is moving. I’m not sure if it’s the thermostat, if there’s a leak I’m missing, or if there’s just a small air pocket somewhere in the coolant lines. All I know, is that the heat works when the car’s moving, and it doesn’t when it’s stopped. It’s bad enough that I’ve spent more on coolant than I have on gasoline, so I’m guessing there’s a leak. I just need a helping hand. Anything would be much appreciated.
Because the engine is a V configuration and is taller than the front of the car, the water level in the engine is higher than the radiator. It is also higher in some places than the water tank at the rear of the engine compartment. Most of the V6 engines have an air bleed at the top most water tube on the engine. This Air Bleed MUST be vented after the engine warms up after filling the system with coolant. It is also possible that the radiator cap or water reservoir cap is tired and not sealing. As the engine cools off it is supposed to suction water out of the water reservoir and put it back in the system, if there is an air leak at a cap it will suction air back into the system rather than water.

So there are 2 must do's when working with the water systems – always ensure the caps are sealing, and Always – Always after opening the system or adding coolant - Vent the system after warm up!!! I learned this by warping the head and blowing the head gasket !
 
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