Piston Slap: A Fusion of Moonroof Drainage Problems?

Sajeev Mehta
by Sajeev Mehta
piston slap a fusion of moonroof drainage problems

Matt writes:

Hi Sajeev,

I’m a long time lurker on the truth about cars, it’s probably of my favorite car website‎!

The problem I’m having is with my 2010 Ford Fusion SEL, I bought it brand new back in May 2009 and now with 175,000KM (Canadian!) it’s been a great car until this recent issue has popped up and neither I or a glass shop or a Ford Dealer can figure it out. I’m getting water in the car on the passenger side A pillar where the plastic trim meats the headliner, the water doesn’t gush in, the floor is never wet just that corner gets wet during heavy rain.

The Fusion is equipped with a moonroof but I’ve had the drains cleaned and even went as far as pouring water down the drain tube that runs along that part of the car and it stayed dry inside, I thought it might have been the corner of the windshield but after using some heaving duty caulking along the top of the windshield it’s still getting wet inside.‎ I checked the moonroof drip tray when the headliner was wet but it has very little water inside the drip tray, I thought it might be the passenger side door seal leaking but it’s also dry inside when the headliner is wet. I can’t seem to figure out where it’s coming from, every time I think I’ve pinpointed it, it gets wet again. I have also noticed that it seems to stay dry most of the time when parked on a flat surface but when parked on any sort of incline it seems to get wet and of course my driveway is inclined. There is these long black plastic trim that runs along the roof on both sides, I always thought it was held down with adhesive but is it possible there are holes underneath that trim?

I’m feeling extremely frustrated at the moment with it, I am?! don’t want to trade it in, I love my Fusion I’ve got the 3.0 litre V6 which gets good mileage and is quick, it’s comfortable and has been reliable only needing one repair under warranty to replace the shifter because the switch for manual mode died, so any help you and the best and brightest can provide would be greatly appreciated.

Sajeev answers:

Thanks for no longer being a lurker! Woot!

I’m thinking the moonroof is the problem, the alternatives are not likely. Bad door weatherstripping? That normally causes leaks further south, as water runs down to the carpet. A leaky windshield isn’t likely considering today’s bonding process at the factory. Remove that caulking you crammed in there, it’s only lowering the Fusion’s resale value and curb appeal.

Plus, if the windshield was the fault, I reckon it’d also be a howling nightmare in stiff cross winds at highway speeds.

The plastic rain gutters are often held with nuts/bolts, but it isn’t a likely defect. Wait just one second! Remember what our friend from the UK, Mr. Edd China, did to find a water leak?

The smoke machine is a brilliant idea, but I suspect it couldn’t find a leaky rain gutter: those are probably sealed away from the headliner quite well.

I keep going back to moonroof drainage for multiple reasons. Put another way, A Fusion of Moonroof Drainage Problems:

  • Glass is out of adjustment, allowing for excessive amounts of water when parked at an angle.
  • Drain tubes are slightly crimped/blocked which exacerbates the problem.
  • The glass’ rubber seal is dirty; dirt reduces the seal’s effectiveness.

A tough problem for sure. I’d clean the seal, clean the moonroof gutters, have someone make sure the glass is adjusted correctly and hope for the best. If not, time to drop the headliner and go for a closer look. No fun, but certainly not impossible.

[Image: Shutterstock user JADEZMITH]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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2 of 53 comments
  • Sector 5 Sector 5 on Jan 26, 2015

    The old Versa hatch had similar. Dealer cure: blast drainage channels with compressed air hose.

  • Scwmcan Scwmcan on Jan 26, 2015

    Probably not your problem, but I had something similar with my Toyota Matrix, in my case it was water getting in around loose bolts for the roof rack mounts ( roof racks not on, but under the plastic trim on the roof the bolts were loose). Don't know if your fusion has something like this, but if it does it is something to look at.

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