Being in the PNW, I fairly quickly noticed that I had a water leak on my new to me 2014 FiST, 100k miles, no moonroof. Its an extra fun car I use (will use) for Autocross.
I looked around here and saw that lots of people had similar issues. I pulled the hatch area apart, and could see water trails rolling into the spare tire area from the corners.
I originally thought it was the vent panels letting water into the car from the tire spray, but after getting the car dried out and sitting overnight in the rain, there was still water in the spare tire area.
So I pulled the tail lights out and found several places where it could leak. Around the brake wire hole and the big hole with a piece of cloth tape over it! After 6 years the tape was mostly falling off.
I cleaned everything, RTV'ed the wire hole, and made a new block off plate out of lexan, and RTVed that all up. I was happy with my solution and figured the problem was solved.
Until the next rain, 1/2-1 cup of water in about 2 hours. Taking the tail lights off again, I saw that the screw holes for holding the taillight housings were the culprit. I could put my hand directly under these holes inside the car, and feel it dripping. I never would believe that that tiny of a hole would let that much water in, but I had an old Suburban with a similar issue. When the windshield was replaced, they removed the cowl trim, and didn't seal up the trim screw that held it in. After that the fan box would fill with water and soak the passenger floor. I tore that rig apart trying to find the source of the leak, refusing to believe that tiny little screw would let in that much water. But as soon as I put a little RTV on the trim screws before re-installing, problem solved.
Back to the Fiesta. I re-installed the tail lights, putting RTV on the screw holes, then I RTV'ed around the top of the tail light to keep water from getting behind the lights in general. I will look for a cleaner solution, maybe foil tape, as a future cleaner fix.
I looked around here and saw that lots of people had similar issues. I pulled the hatch area apart, and could see water trails rolling into the spare tire area from the corners.
I originally thought it was the vent panels letting water into the car from the tire spray, but after getting the car dried out and sitting overnight in the rain, there was still water in the spare tire area.
So I pulled the tail lights out and found several places where it could leak. Around the brake wire hole and the big hole with a piece of cloth tape over it! After 6 years the tape was mostly falling off.
I cleaned everything, RTV'ed the wire hole, and made a new block off plate out of lexan, and RTVed that all up. I was happy with my solution and figured the problem was solved.
Until the next rain, 1/2-1 cup of water in about 2 hours. Taking the tail lights off again, I saw that the screw holes for holding the taillight housings were the culprit. I could put my hand directly under these holes inside the car, and feel it dripping. I never would believe that that tiny of a hole would let that much water in, but I had an old Suburban with a similar issue. When the windshield was replaced, they removed the cowl trim, and didn't seal up the trim screw that held it in. After that the fan box would fill with water and soak the passenger floor. I tore that rig apart trying to find the source of the leak, refusing to believe that tiny little screw would let in that much water. But as soon as I put a little RTV on the trim screws before re-installing, problem solved.
Back to the Fiesta. I re-installed the tail lights, putting RTV on the screw holes, then I RTV'ed around the top of the tail light to keep water from getting behind the lights in general. I will look for a cleaner solution, maybe foil tape, as a future cleaner fix.
