Here’s the situation: the Ford Transit has several mounting points (M8 threaded holes) to install roof rack and accessories to the roof. Each mounting points is a M8 threaded hole, with a painted rubber plug on top of it to prevent water infiltration. Unfortunately, it is not uncommon for the threaded holes to develop slow leak over time. We know, it shouldn’t be like that. But no vans are perfect; the Transit, Sprinter and ProMaster each have their own little problems… So instead of getting mad about it, we’d rather take a few minutes to permanently fix the problem and keep our energy and a positive attitude for the next steps of our van conversion 🙂 Let’s do it!
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1. About Slow Leaks
Slow leaks are evil and have the potential of creating quite a lot of damage. Indeed, a slow leak can go on for a long time (days, weeks, or months) without being noticed. During that time, moisture is trapped (e.g. in insulation or in the ceiling cavities) and mold can develop.
2. Leak Causes & How To Fix
2.1. Roof Plugs
The Ford Transit has plugs at each of the mounting points for roof rack and accessories, as well as pass through holes to run electrical wires (or such):
The paint over the plug may crack over time and allow slow leaks:
On our 2016 Transit, after 6 months of full time vanlife, we noticed dripping water coming out of the wall over the sliding door; because our ceiling is insulated and finished, we could not locate the exact location of the leak. But we assumed it came from one of the threaded hole, so we climbed on the roof and we found that the paint was slightly cracked around the plugs (see previous picture).
It is worth mentioning that not everyone is having water leak issue on their Transit. Many people didn’t do anything about it and are doing just fine. You may, or may not encounter this. That being said, the fix is so easy that we’ll personally do it on our new 2021 Transit just for our peace of mind.
The solution to prevent the roof plugs from leaking is pretty simple: seal the plugs with sealant! Because you, or the next owner, might eventually need to remove the plugs, we’d recommend using a non-permanent sealant, such as Dicor Lap Sealant (see on Amazon).
We were in Montana when we noticed the leak, it was winter, and we had to solve the issue quickly on-the-spot. Silicone II is all we could find locally at the hardware store, so we went ahead and proceeded to seal the plugs. No issues since then!
2.2. Roof Panel Joints
The Ford Transit roof is made of several sheet metal panels, joined and sealed together:
Unfortunately, at some spots, the factory sealant may be inappropriately applied and allow slow leaks:
A few weeks after getting our 2021 Transit, we noticed a tiny spot of water on the cargo floor:
We climbed on the roof and we located where the sealant wasn’t properly applied (see “Gap In Sealant” in picture above). To prevent any leak in the future, we decided to seal all the panel joints on the roof (marked with a red line in the picture above) as follows:
- Mineral Spirits
- Soapy Water
- Sikaflex-221 (or another sealant of your choice)
- Caulking Gun
- Shop Towels (or a lint free cloth)
- Nitrile Gloves (we pre-cut a bunch of fingers, see step 3)
Remember to keep soapy water nearby at all time, this stuff is pretty sticky!
1. Clean the surfaces to be sealed (we used mineral spirits, soapy water is probably fine though):
2. Apply sealant (we used Sikaflex-221, same sealant as for the roof rack install):
3. To smooth out the seam, wet your finger in soapy water and run along the sealant:
4. Final result (with roof plugs removed for the roof rack installation). Looking good and clean!
Food for thought
Because we insulated our van using Thinsulate (faroutride.com/thinsulate), water from the slow leak found its way down; we were alerted of the leak shortly and we could fix the issue at the source. If we had use foam board or spray foam (or whatever), water would probably have been trapped and accumulate somewhere (remember some of the threaded holes are hidden within frames) and rust over time or drain all at once when driving and make a huge mess. Also, as opposed to denim or fiberglass insulation, Thinsulate is hydrophobic and don’t retain moisture; it will dry soon enough. We think that’s another good reason right there to choose Thinsulate for insulation…