Water leaks in your car can be a real nuisance, leading to musty odors, damp carpets, and potentially even rust and electrical issues. Just like maintaining a classic Mercedes W123, addressing leaks promptly is crucial for any vehicle’s longevity and comfort. Recently, we encountered a significant water leak in our family’s 2015 Ford Fiesta. Despite being a reliable and economical car, even modern vehicles can fall victim to water ingress over time. With over 125,000 miles on the clock, our Fiesta had served us well, requiring only routine maintenance and replacement of wear-and-tear parts like the interior fan resistor, stabilizer links, and suspension springs. However, the sudden appearance of water in the passenger footwell and spare tire well signaled a more serious problem that needed immediate attention. Armed with some tools and a can-do attitude, we decided to investigate and tackle this DIY repair.
Fiestas, like many cars, are known to develop leaks eventually. A quick search online reveals numerous helpful videos detailing common leak points. Often, water in the front footwell is attributed to a blocked air conditioning or heater drain, caused by accumulated debris or damage from speed bumps dislodging the heat shield. However, our issue was located in the left rear, pointing towards three potential areas: the rear light unit seal, the bumper area, or the roof trim/rail.
To get a better understanding of the problem, we moved the Fiesta into our workshop.
Our first step was to meticulously trace the water leak. The extent of the problem was immediately apparent. The carpet and underlying felt were saturated, the boot trim was damp, and there was a noticeable pool of water, about 1cm deep, in the spare tire well!
To gain access to the potential leak areas, we began by removing the interior trim and the rear left light unit. Interestingly, changing a rear light bulb in this model requires removing a significant amount of trim to access the securing nut – a testament to modern car complexity!
For better access and visibility, we also decided to remove the rear bumper. Held by a couple of screws and plastic fasteners, it was relatively straightforward to remove, albeit a bit awkward to handle alone.
With the trim and bumper removed, the next crucial step was thorough drying. We took all the removable trim indoors and spread it over central heating radiators to expedite the drying process, especially since the outside temperature was near freezing.
We then used workshop wipes and towels to absorb as much standing water as possible from the car’s interior.
To tackle the soaked carpet and felt underlay, we positioned a workshop air heater inside the car, directing warm air towards the affected areas. Creating a makeshift tunnel helped to concentrate the heat and improve drying efficiency.
Before dismantling anything, we consulted online resources and the car’s workshop manual for guidance on removing the rear light unit and other components. This preparation is essential for any DIY car repair, whether you’re working on a modern Ford Fiesta or a classic Mercedes W123.
One potential leak source we identified was the cabin air vent, a flapper device hidden behind the bumper designed to allow air to escape the cabin. These vents use rubber gaskets that can become brittle and fail over time. We removed the vent, cleaned the area, and reinstalled it using sealant to ensure a watertight seal.
We also focused on the rear light unit mounting area. This area relies on a gasket to seal against the chassis, and rainwater running down the bodywork could easily penetrate if the seal is compromised. We applied sealant liberally around the mounting points to ensure a robust seal.
In a surprising discovery, we found that Ford uses tape to seal some chassis openings. While perhaps adequate when new, this tape can degrade over time, becoming another potential leak point. This highlights how even seemingly minor details can contribute to water leaks in cars.
We replaced the degraded Ford tape with a DIY sealant tape, ensuring these chassis openings were properly sealed.
We opted for an RTC sealant, known for its good adhesion to metal and ease of removal if needed in the future. Having a variety of sealants on hand is always useful for car maintenance.
While working on sealing the exterior, we continued drying the interior using the air heater, creating a tent with a blanket to trap the warm air and maximize drying efficiency. This method has proven effective in previous car restoration projects, even on classic cars like an Alfa Spider.
After a day of drying and sealing, we reassembled the car, applying sealant to all gaskets and mating surfaces. We also replaced a few broken plastic fasteners – keeping a stock of these is always handy for car repairs.
Unfortunately, despite our efforts, heavy rain overnight revealed that the leak persisted. This meant we had to investigate further, this time focusing on the roof trim/rail.
Removing the roof rail was surprisingly easy. As we learned from a Ford mechanic, it’s held in place with double-sided tape. A quick pull, and the rail was off!
Upon closer inspection, we discovered a small crack in the weld along the roof line. This crack was likely the primary source of the persistent leak.
We also identified other potential problem areas around hinges and overlapping metal sheet parts, as pointed out by the helpful Ford mechanic.
We spent considerable time carefully sealing all identified cracks and potential ingress points along the roof line with sealant. Given the cold temperatures, we allowed ample curing time in the workshop overnight to ensure proper sealing.
This comprehensive leak repair job took approximately 10-12 hours, with a significant portion of the time dedicated to drying and cleaning. While a dealership might charge for roof rail repairs and leak tracing, tackling it yourself can save considerable costs and provide a thorough solution.
Tracing water leaks can be challenging due to limited access and visibility within car chassis structures. While we suspect the roof weld crack was the primary culprit in our Fiesta’s leak, addressing other potential points like gaskets, vents, and even factory tape ensures a more robust and long-lasting repair. Hopefully, our Fiesta will remain dry for many miles to come, much like a well-maintained classic car such as the Mercedes W123 known for its durability. Fingers crossed for a dry future!
