George993

Experts,
We are all familiar with poorly designed Mercedes sunroof drainage but that seems to not be the case (single not pano sunroof btw). The sunroof draining holes drain ok. The water does not accumulate at the sides, but the largest amount comes down from the rear view mirror in the car center.

Are the W212 cars known for leaking windshields? The windshield is Mercedes branded so most likely original (or dealer replaced). The sealant at the top of the windshield turned into a goo with cracks, as it normally does in Mercedes cars used in hot climates, but I would still expect enough sealing capabilities left.

The problem only appears after the Florida heavy rains, so may not be noticeable in less extreme climates. Thoughts? Thx

CaliBenzDriver

You have this leaky windshield topic well summarized

You live in sun drenched Florida, so the seal chemistry has plenty of reasons to fall apart with UV + Heat cycles. Perhaps there is a white sealand that can do a better job. Swing by a car glass shop to inquire.

Until repaired, try to cover the top of your windshield seam with shipping tape (good luck cleaning that!) to keep rain out of priceless MFK camera, sunRoof OCP.

I think both sides also been found to leak: cover sides!

Painters tape is easier to remove but not water proof.

We can almost bet many of us in warmer climates have this failure baking to maturity. Would you mind showing us the degraded windshield sealant so we can identify it ???

Thank you.

MDPensfan

I have a leak that I thought I had resolved by blowing compressed air into the sunroof drains, then running water through the drain holes and watching it leak out in the wheel well. Had a few light rains and a couple car washes since then, no issues. Had a windy, heavy rain last night and was greeted again by water on the center console, moist seats, and water accumulating in the footwell. Not a ton, but certainly enough to irritate me and ruin my morning.


I checked the windshield seal after reading this post, but I didn't see anything that looked amiss. Just looked like a black, intact, rubber seal across the top of the windshield. I suppose it could still be my sunroof drain. I opened the sunroof and didn't see any pooling water along the front channel. The drain holes didn't look full and didn't blow back any water when I used compressed air in them again. Maybe they're draining slowly and when there's a heavy rain the impaired drainage makes them back up and leak into the cabin, then they are able to slowly drain when the rain subsides.

I just checked and the A pillars on both sides are wet (more so on the driver's side) so the more I think about it, it must be the sunroof. I think I recall a post from my research when I first had a leak about being able to cut off the end of the drain tube filter thing in the wheel well, as that sometimes gets clogged with debris. I'll give that a shot later as I really don't need my seats and assorted electronics getting wet repeatedly. Last time this happened the cabin heat was a little off until everything dried out.

CaliBenzDriver

the windshield gasket may have shrunk off the surface.... try to water with a localized jet of water to pin point.

Beware of your SAM Fuse Box becoming water logged from A pillar channel.

George993

Thanks @CaliBenzDriver it could be the seal (no point to post a photo as little is seen, just deteriorated rubber in the slot). I'll try re-sealing or test taping but thinking more about it, a factory windshield is not likely to leak even if several millimeters of the seal was to be gone. Looking at windshield replacement jobs, the applied sealant covers quite a wide area and does not harden. Rain is not applying much pressure so it's just a volume of water.

It may be sunroof after all (despite being tested and draining with small amount of water). Mercedes made two big errors designing the sunroof drainage - too narrow drain pipes comparing to what over cars are using (probably cost justified) and the end of pipe instead of being open to drain rests on some little shelf to restrict the draining and aid with clogging it up. Those two errors combined could be enough to overflow in heavy rains, specially in older cars which also have the main sunroof seal less than perfect.

BTW, in W221 S class Mercedes made a third sunroof draining error by making the plastic tray under the sunroof to crack and leak (ask me how I know) but I have not seen reports of the W212 doing that. But it could still be a possibility, maybe there is a crack in the plastic as well, causing overflow once the water is not draining fast enough, before an overflow over the top of the tray is happening.

So correcting the second design error looks like a next step.

KEY08

So, you haven’t completed a hose test at the roof/ windshield junction? Flood that area and see what happens.

George993

@KEY08 test completed on both sides, the issue is amount of water coming out of the hose. Little water - good draining, lot's of water - no way it could drain even in a perfect brand new car at the factory.

MDPensfan

Yeah, I think you hit the nail on the head there. I peeled back the driver’s front fender well to see where the sunroof drain terminates, but I couldn’t see it. I know both sides drain, but it’s leaked into the car twice after heavy rains and with the front of the car facing downhill, so the water just overwhelms the tiny drain holes/hoses and it backs up.

I gave the sunroof and top of the windshield a good water test today when washing my car. Bone dry. I’ll start parking the car with the rear facing downhill and hope that keeps any rain/melting snow from flooding the drain holes.