Water leaking into Trunk

[David86]

Hello forum members,


First of all, sorry for my poor English. I’m from Germany and I’ll try my best to explain the issue.


I own a 2024 Mustang with the Performance Package, and I’m experiencing water leaking into the trunk through the bodywork. Whenever it rains, water comes in at exactly the same spot.


My Mustang has already been at Ford twice, five days each time, to fix the problem. Unfortunately, it still leaks whenever it rains. They have already removed the entire rear end to find the issue and replaced all the seals, but without success.


The only things that have not yet been tried are removing and inspecting the rear window, as well as the third brake light.


Has anyone experienced similar issues with their vehicle and/or had the problem successfully fixed by Ford? Both times, Ford was absolutely certain the issue had been resolved — unfortunately, without success.


Thank you in advance for your help.

Sponsored

 

[SSuperDave]

I have not seen that complaint yet, and there are no relevant TSB's or special service messages. Normally, when they are plainly as visible as that, they are easier to find.

 

[Skye]

https://www.mustang6g.com/forums/th...ater-leaking-into-rear-quarter-panels.143545/

https://www.mustang6g.com/forums/threads/water-intrusion-from-rain.181066/

https://www.mustang6g.com/forums/threads/cracking-at-top-of-a-pillar-2017-gt-convertible.171259/

Vielleicht eine Nahtstelle an der Karosserie im Bereich des Fensters? Das kommt zwar selten vor, aber kleine Risse können zu Undichtigkeiten führen. Oder eine Stelle, die kaum oder gar nicht abgedichtet ist, benötigt etwas Abdichtung.

Maybe a unibody seam associated with the window? It is not common, but small cracks can develop into leaks. Or, an area with little to no sealer needs some.

 

[SSuperDave]

Sehr gut!

 

[Charger68]

Tell the dealership someone there needs to get into the trunk. Close the lid, run water over certain body areas one at a time to find the source of the leak. I learned that from a former Honda and other makes mechanic.

 

[SSuperDave]

We also sprinkle baby powder on it to see where the trail begins. At the dealership level, squeaks, rattles, wind noise and water leaks are the worst thing to deal with.

 

[David86]

Thank you very much for all your help. I received a new appointment for next week today.


The service manager assured me that, as the next step, they will remove the rear window and inspect the third brake light. He basically wants to rule out everything else, since during the last appointment the rear bumper was removed and the entire trunk was disassembled into its individual components.


They also tried to locate the leak using a smoke (vapor) generator, but unfortunately they were unable to detect any leaks during their tests—even after spraying the car with water for 30 minutes. Strangely, the issue only seems to occur when the car has been parked in the rain for several hours.

 

[Wiley Marmot]

Herzlich willkommen und es tut uns leid, von Ihren anhaltenden Problemen mit dem Kofferraum zu hören!

From the pics you posted; it looks like you've isolated the entry point of the leakage. Would you be willing to consider spraying that area with a water proofing material (rubber or silicone based?) of some sort as a blanket type seal?

PS: Keine Sorge! Dein Englisch ist viel besser als mein Deutsch!

 

[David86]

I’ve already considered the idea of sealing the entry point. However, that wouldn’t actually fix the underlying problem. Water could still collect or even pool somewhere inside the body of the car.


Since I drive the Mustang daily all year round, and we use quite a lot of salt on the roads here in winter due to ice and snow, that salt water could potentially get into areas of the vehicle that aren’t protected against rust.


When I bought the car, I had it fully undersealed because, unfortunately, in Germany there’s a common belief about American cars that they aren’t properly galvanized from the factory, let alone well painted. Sadly, I’ve already had to realize that the factory paint from Flat Rock is really a joke—Ford could definitely learn a thing or two from other manufacturers in that regard.


At the end of the day, it’s important to me that a new vehicle is in good condition. I think it’s only fair that Ford fixes this issue without any hassle.

 

[David86]

Hello dear forum members,


I’d like to come back once again to the issue with the water leak in my car.


In general, I expect all my cars—whether VW or Porsche—to be able to stand outside in rain and snow. A Ford should also be built to handle that.


It all started in autumn going into winter 2025, when I noticed while loading and unloading that the carpet in the trunk felt slightly damp. At first I dismissed it as possible condensation and didn’t think much more about it. I also put a temporary rubber mat in the trunk.


Then in January, after a winter night with snow and rain, came the surprise: a small puddle in the trunk, with water droplets forming on the upper side of the body.


I called my Ford dealer and made an appointment. During the appointment they tried to locate the leak from the outside, and two external weld seams that meet near the trunk were repaired with (presumably body sealant) and repainted.


I was able to pick the car up again after three working days.


A few days later, after nighttime rain, I opened the trunk and there was another puddle—this time even frozen.


So I called Ford again and made another appointment. In the meantime I had also tried to research the issue in forums, including here, to see whether similar problems were known. Unfortunately, there are only many similar stories about the previous model (problems with the rear window / the transition under the rear window).


When I dropped off the car for the second appointment, I repeatedly suggested that the rear window might be the cause. So the car went in for round two.


A little over a week later I was able to pick up the Mustang again.


Conclusion after a longer discussion with the body shop technician at my dealership:
The entire rear trim and trunk trim were removed. The trunk seal was replaced, and all seals in the lower body area of the vehicle were repaired or improved. HOWEVER, no visible leak could be reproduced or found.


At the same time I was told several times: “It can’t be coming from the rear window—it looks fine.”


At that point I had already started putting some pressure on Ford Germany to take a closer look at the issue as well.


Less than three days later there was heavy rain.


Result: the trunk was swimming.


I called Ford again and made another appointment. When dropping the car off, I strongly insisted that they finally consider the rear window.


During the third round, Ford Germany / Europe also got involved. I’ll spare you the details of who discussed what, when, and where.


After two and a half weeks, I finally got my car back.


Result:
The rear window was removed. The bonding flange of the window at the lower center was not properly aligned, which was the first possible point of water entry. The second—and confirmed—source of water ingress were the transitions of the roof channel on the left and right, both at the top and bottom. Extremely fine hairline cracks were found there. Only after very long exposure to water could a kind of capillary effect occur, allowing a small amount of water to seep in and run downward.


From the inside, they sprayed a foam-like water mixture until foam appeared at the leaking points.


All affected areas were reworked, then sent to the paint shop, and the rear window was properly reinstalled and sealed.


The whole process really cost me a lot of energy and nerves.


At the end of the day, I’m very happy that something was finally found. Of course I’ll have to keep an eye on it in the coming days and weeks to see whether it really stays sealed. At the moment, however, I’m optimistic and hope the problem has finally been identified.


I’m also aware that probably 8 out of 10 Mustangs are fair-weather garage cars. Even if they had the same defect, it might never show up because the cars are rarely exposed to water for long periods.


Ford Germany hinted to me that if this turns out to be a recurring issue, it could quickly lead to a larger recall.


I hope I can close this chapter now. Today, while driving in the sunshine, I felt like a little kid again, and the four weeks in the workshop were quickly forgotten.


And if anyone experiences the same shock I did, feel free to reference my post or contact me directly. I still have many more photos.


Of course I also asked how many working hours and how much effort my Ford dealer had invested overall.


Let’s just say that well over €5,000 (5800,- USD) in labor, materials, and paintwork must have gone into this.


So I can only recommend discovering this defect while the car is still under warranty.

 

[LarryOS650]

Thanks for sharing. I hope this fix finally solved you issue.

 

[Charger68]

OMG. I’m glad it’s resolved. I would given up, and demanded it declared a Lemon. Interesting since my car sits out the Winter.
I once bought the new 1980 four-speed Corvette, and the T-tops couldn't be aligned "any better". The passenger side had a 1/4" gap at the rear, and the driver side 3/4". It never mattered until I replaced the door and A-pillar weather-stripping, and then my driver side door glass barely made it rearward to the C-pillar weather-strip. I measured both door glass and the driver's opening was 1/2" longer than the passenger side's. The roof was bonded on crooked. I asked a glass company if they could made me a door glass, to which they said yes, for $500,000. They gave me extra flat rubber piece to sandwich ahead of the A-pillar garnish molding, which moved the door glass reward more.
Trying to get the weather-striping on this car, the tops, doors, and windows, took days and hours into many mornings to get right.

Sponsored