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Discussion Starter #1 (Edited)
09.09.2020 Update: Incorporated helpful follow-up comments from @jimmyfloyd which GREATLY simplify the process. Thanks!

Originally I posted this as a question in the maintenance forum. I've since replaced the cooler lines successfully and will describe the procedure here.

Background: Found transmission fluid leaking onto the ground directly underneath of the radiator. Removing the lower engine splash shield that is attached to the bumper revealed that the transmission cooler lines were rusted through and the fluid was pooling on top of the splash shield before leaking to the ground. This G6 had 71K miles on it during the time of the leak.

Here's what the rusted lines looked like:

s_IMG_5462.jpg

Depending on how well you know your way around the g6, the job could take anywhere between 2-4 hours. My familiarity with the car prior to this job only included oil changes, brake pad/rotor replacement, tranny filter/pan gasket replacement, and spark plugs so it took me about 4 hours.

Replacement part was ACDelco 15212982

1. Remove the lower engine splash shield under the radiator. It's held on by 4 plastic clips and 5 screws.

2. Remove the nut securing the cooler line bracket to the transmission. Pull the bracket/lines out of the transmission and have a catch-pan ready as some fluid to come out.

3. Detach the white retainer clip holding both lines to the radiator support.

4. To access the nut connecting the lower cooler line to the radiator, remove the radiator support bracket that is directly below it. The support bracket is attached to the frame with two bolts. After removing them you can twist the bracket out of place. This can be a bit of a pain because there's a plastic panel immediately to the right of the bracket that restricts its movement. Removing a few plastic clips should help and allow you to pry the paneling back while you twist the bracket out of place. Once you've gained access to the nut, remove it while having your catch-pan ready pry off the black plastic retainer. Next remove the metal retaining clip and pull the line out from the nut. Save the metal clips for reuse with new lines.

5. Next you'll need to reach the nut securing the upper line to the radiator. If you remove the outlet duct you can easily reach it from the top, but to remove the nut you'll need either a crowfoot wrench or something similar that will allow you to unscrew it from the awkward angle. Since I only had regular open wrenches available, I removed the right headlight assembly to gain easy access to it. As @jimmyfloyd pointed out, you DO NOT need to unscrew the radiator nuts securing the cooling lines but according to him it still sounds like removing the passenger side headlight assembly made it easier to access the upper nut. Remove the upper line using the same method as with the lower line.

6. Pull the old lines completely out from under the car. Next I removed the two radiator connector nuts from the old lines to reuse with the new lines. First remove the black plastic retainers by easliy prying them off. They will expose the metal retaining clips that secure the nuts to the lines. These can be removed with tweezers or a pick. Once both retainer clips are off, twist the connector nuts off of the lines.

7. Install the connector nuts onto the new lines and secure them with the existing metal retainer clips. Finally, slide the black plastic retainers over the nuts (new cooler lines should include new plastic retainers).

8. Fit the new lines into position from under the car. I installed the transmission-side bracket first, then attached the white clip to the radiator support, followed by the lower radiator nut, and finally the upper nut. Be aware that when you go to screw the lower nut back into the radiator, the fitting that it threads into will give way when you press on it and coolant will drain out until you manage to fully screw the nut back in, so have the catch-pan handy.

Insert the new lines into the radiator nuts and secure using previously removed metal retaining clips. Slide new black plastic retainers (included with new lines) over the nuts.

9. Re-install all other parts you removed (e.g. radiator support bracket, splash shield, etc).

10. Remove the 11mm transmission plug to get ready to check fluid level when topping off ATF (Dexron VI). Remember to top-off while the car is running.

Reference photos below.

Cheers!

s1_IMG_5456.jpg s2_IMG_5459.jpg s3_IMG_5463.jpg s4_IMG_5466.jpg s5_IMG_5467.jpg s6_IMG_5471.jpg
s7_IMG_5474.jpg
 

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Do NOT follow this How To exactly. You may possibly end up with issues trying to get things back together.

In Steps #4 and #5, do NOT remove the nuts as stated. This is important. Leave the nuts in the radiator and remove the clips that are mentioned in step #6. This is how it is meant to be removed and why the nuts are not included.

I did follow this How To to the letter, and when I went to put the nuts back in, I found that the Trans Cooler is actually free moving in the radiator, and is meant to be held on with those nuts. Mine moved back into the radiator and I had to fight for 20 minutes to finally get one of the nuts started and tightened enough to get the other started. The liquid that is mentioned in #8 is actually Coolant that flows past the Transcooler.

Aside from this, the rest of the How To worked well for me. Removing the headlight made it easier.
 

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Hello did you figure out why it was leaking?? Because I'm having the same exact problem to the T I had my radiator replaced and that's when my problem started the shop said the fittings were defective had those replaced and still same issue that's why I ask please let me know how you fixed it also thanks ahead of time
Allen
 

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I don't recall. I worked on the car over 3 years ago, and no longer have it. I don't even know if I removed it to replace something that was leaking or just to flush it.
 

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Discussion Starter #5
Hello did you figure out why it was leaking?? Because I'm having the same exact problem to the T I had my radiator replaced and that's when my problem started the shop said the fittings were defective had those replaced and still same issue that's why I ask please let me know how you fixed it also thanks ahead of time
Allen
The transmission lines rusted through and started leaking.
 

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The transmission lines rusted through and started leaking.
I didn't get to it today but I do have one last question you can hopefully answer which is the fittings on the trans cooler end if you recall there being orings or if it's just the flare fittings???? Thanks again
 
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