Leaking Rear Window Seal/Seam

[Big Bird]

Spent some time washing the Mustang yesterday afternoon and was met with a small puddle in the trunk while drying everything off. After some further inspection, it seems that water is making it's way through the rear window seal, through the metal seam underneath, and into the trunk. It was not a massive amount of water, but there was evidence (dried water drops) that shows that this has most likely been an issue since the car left the factory.

I'm not losing too much sleep over it, as the car is rarely left outside and Arizona tends to be fairly dry, but it does need to be addressed at some point. I'll most likely have my local Ford dealership take a look at this whenever I get around to bringing the car in for the BCM corrosion recall (25C43/25V546).

Has anyone else encountered this same leak on their S650 and/or S550 Mustang?

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[Will2]

Where is the water entry point, rear quarter window like my pic here?

Rear quarter window trim peeling? | Mustang7G - 2024+ S650 Mustang Forum (Dark Horse, GT, EcoBoost, GT500, GT350, Mach 1)

I will check my trunk.

 

[Big Bird]

Where is the water entry point, rear quarter window like my pic here?

Rear quarter window trim peeling? | Mustang7G - 2024+ S650 Mustang Forum (Dark Horse, GT, EcoBoost, GT500, GT350, Mach 1)

I will check my trunk.

Water entry point seems to be somewhere in the weather seal strip that runs along the bottom of the rear window (most likely towards the passenger side). Unrelated to the trim on either of the rear quarter windows.

 

[AZ_Ryan]

Spent some time washing the Mustang yesterday afternoon and was met with a small puddle in the trunk while drying everything off. After some further inspection, it seems that water is making it's way through the rear window seal, through the metal seam underneath, and into the trunk. It was not a massive amount of water, but there was evidence (dried water drops) that shows that this has most likely been an issue since the car left the factory.

I'm not losing too much sleep over it, as the car is rarely left outside and Arizona tends to be fairly dry, but it does need to be addressed at some point. I'll most likely have my local Ford dealership take a look at this whenever I get around to bringing the car in for the BCM corrosion recall (25C43/25V546).

Has anyone else encountered this same leak on their S650 and/or S550 Mustang?

Oh man. I haven't had a leak in the trunk like that. It seems like Ford really screwed up making these thing water tight.

 

[Big Bird]

Just picked my Mustang back up from the local Ford dealership and they seem to think that they were able to locate/resolve the source of the leak:

verify concern inspect for water leak mt remove rear scuff plate and interior trunk panels upon inspection found RR tail light harness boot not fully seated to body reinstall boot plug reinstall lamp perform water test no leaks reinstall plate and interior panels ck pass

I have my doubts that reseating this rubber tail light harness plug will actually fix the issue here, but won't be able to confirm until the next time I wash it. I'm still fairly certain that this leak is being caused by a poor seal at the bottom of the rear window, but would love to be wrong about that.

 

[AZ_Ryan]

I've been meaning to post on this.

I washed my car over the weekend. And when I opened to trunk to dry around the lights, I noticed that collected water from under the spoiler ran down the side on the decklid and drained in the exact same spot you showed.

It was not a leak. But just the natural path that the water took when I opened the trunk.

Any chance this is what happened on yours, and you just thought it was a leak?

 

[Big Bird]

I've been meaning to post on this.

I washed my car over the weekend. And when I opened to trunk to dry around the lights, I noticed that collected water from under the spoiler ran down the side on the decklid and drained in the exact same spot you showed.

It was not a leak. But just the natural path that the water took when I opened the trunk.

Any chance this is what happened on yours, and you just thought it was a leak?

I am familiar with the spoiler drippage that you are referring to, but I think this is different. The dried water trails in the trunk lead me to believe that water is intruding through the seam that is highlighted in my original photos. That being said, I would certainly prefer your theory.

Upon some further Internet forum sleuthing, I was able to find a handful of other examples of this specific leak occurring on some S550s as well (trims from EcoBoosts up to GT500s). Unfortunately, it seems that the resolution for those was to potentially have the rear window removed, resealed, and then reinstalled.

 

[sdsteele2]

I had a similar if not the exact same leak on my 2020 S550.
There is a seam where several panels join along the C pillar and under the edge of the glass. There was a burr on the edge that was preventing a full seal and allowing water to leak past. The dealer tried a few fixes but in the end the only way was to remove the glass and smooth out the seam.
My only complaint was the dealer had to farm out the glass work. The glass shop was terrible. The glass was misaligned, the rubber strip along the bottom was messed up, the rear trim was not installed correctly, and they got urethane sealer on the trunk and bumper. Fortunately the dealer took care of it and I had a loaner while they sorted it out.

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