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On the subject of leaks and drains, it's spring, and my entire neighborhood has young maple trees everywhere. this means, many small "propeller seeds" are getting on (and some in) my car daily. I have been vacuuming out near the windshield wipers but I think I'll be doing something more drastic soon. I flushed out the "side drains" last year and they were OK.
Be sure to check the rubber flap coming from the passenger side windshield edge to the whipper cowl. There is a drain on the cowl at that point. Age and weather can deteriorate the rubber where it no longer directs water to the drain. The water flow off the cowl past the drain and finds its way into the cabin. I glued a piece of weather stripping used for house doors to the cowl to fix that problem.
My experience is with a 2011 E350
Be sure to check the rubber flap coming from the passenger side windshield edge to the whipper cowl. There is a drain on the cowl at that point. Age and weather can deteriorate the rubber where it no longer directs water to the drain. The water flow off the cowl past the drain and finds its way into the cabin. I glued a piece of weather stripping used for house doors to the cowl to fix that problem.
My experience is with a 2011 E350
Do you have couple pics of this MB favorite detail?
This is what's used to channel water to electricals.
I've looked at this drain once and could not find that trap
Here is a picture of the drain. You can see how the rubber I am holding is cracked and actually part is missing. As water runs off the front window it should drain into the vented area shown. The damaged rubber flap stops it from going past the drain. To stop the flow from going past the drain I glued the textured rectangle piece you see by the drain. Located at bottom of windshield on passenger side.
Here is a picture of the drain. You can see how the rubber I am holding is cracked and actually part is missing. As water runs off the front window it should drain into the vented area shown. The sun damaged rubber flap stops it from going past the drain.
To stop the flow from going past the drain I glued the textured rectangle piece you see by the drain.
Located at bottom of windshield on passenger side.
Nice one, thank you!
How is the driver side doing...
also one rain away from flooding electricals?
The driver's side cowl drain is a different layout. I'm not experiencing any issue there. I found this problem while trying to track down a problem with my display for the Command system. My problem is the screen on the command system. The audio works fine, just the screen is black also no picture from the backup camera.
Here is a picture of the drain. You can see how the rubber I am holding is cracked and actually part is missing. As water runs off the front window it should drain into the vented area shown. The damaged rubber flap stops it from going past the drain. To stop the flow from going past the drain I glued the textured rectangle piece you see by the drain. Located at bottom of windshield on passenger side.
2011 to 2025 = 14 years.
The rubber weather strip you are holding , is it also "sticky" ? Aside from the cracking.
It seems more sunlight damage , aside from 14 years of age...yes ?
I too been wondering how long it will last for , if for a sun protected garaged car.
My issue is best viewed in your second picture. You can see the drain grate next to where the wiper attaches. My damaged part comes from the edge of the windshield down to the cowl. Yours looks in good shape.
So for the benefit of the group and posterity, I will share my W212 2013 E Class leak saga. I've had this car since 2015, almost 11 years now. It parks outside, on my driveway which is sloped toward the street. For a variety of reasons, I back into the parking space. We also live below sycamore trees here in Marin County, which put off an awful lot of debris. Leaves, pollen, and all manner of detritus. They are messy trees. Same house for 30 years, ultimately drain problems with all our cars, including all manner of BMWs before I became an MB guy, my wife's old GTI, and a 18-year stint with a chevy tahoe. All developed leaks sooner or later...and the BMWs were just horrendous.
I've been amazed...I thought...at the resilience of my E350 in the leak category. The cowl drains seemed so simple, and (I thought) were engineered so the drainage holes below the cowl drains were larger than the gaps in the drains themselves.
This year, after some big rain storms, I experienced the leak onto the driver's floor mat. For whatever reason, the driver's side cowl drain started to have more debris than usual, and I ended up having to clean it basically every day. This year's pollen was a sticky sort, different than years past, and I noticed it on the ground and elsewhere on my car...just a sticky mess. After a couple of big downpours, it got beyond a simple leak...now it was standing water, crazy. Also, there was something of a bathtub ring of pollen all the way around my cowl, extending across the middle and over to the passenger's side. What was also weird was that the passenger side drain didn't seem to be clogging, the pollen massing I was seeing on the driver side was not happening there.
I reached out to my regular mechanic, who I trust: "We don't do leaks"; and rather than heading to the dealership with an open wallet, I thought I'd dig into this more myself.
So I looked on this forum...inconclusive. ChatGPT wanted me to take off the windshield wiper on the drivers side and pull off the cowl cover. I got halfway thru that exercise and poured some water down and it was draining just fine. So I took my attention to the passenger side. OH. MY. GOODNESS. A couple of posts up this thread, you can see the passenger cowl drain where the sun damage on the rubber was being discussed. Net-net, the passenger drain feeds into a funnel-sort-of-thing and then below the funnel it turns inward into the HVAC system, and seems to share a drain with the HVAC system...interesting engineering. That whole drain system was plugged up with pollen, dirt, mud, pine needles etc. So ALL the drainage that was happening in the cowl area on both sides was draining thru the driver side drain.
I had to take off the battery cover, and then saw more of the integration between the two. With some light digging with long thin screwdrivers in both that funnel below the cowl drain, along with some more digging in a similarly clogged drain well below the HVAC fan, I started to make some progress. Used my dyson vac with some rigged attachments to suck out the detritus bit by bit. I ran a weedeater nylon line between the funnel and HVAC well. Slowly the flow started to get better when running pitchers of water thru it.
Ultimately, I've gotten it to the "it doesn't back up". ChatGPT wanted me to take apart the whole engine-side of the cabin filter assembly, but that looked like a job I didn't want to start. It seems to drain decently now, and given that it's taken 11 years to get to this point, I feel like I've bought myself some good time.
But my goodness, what a silly setup to run the cowl drain through the HVAC system!
So for the benefit of the group and posterity, I will share my W212 2013 E Class leak saga. I've had this car since 2015, almost 11 years now. It parks outside, on my driveway which is sloped toward the street. For a variety of reasons, I back into the parking space. We also live below sycamore trees here in Marin County, which put off an awful lot of debris. Leaves, pollen, and all manner of detritus. They are messy trees. Same house for 30 years, ultimately drain problems with all our cars, including all manner of BMWs before I became an MB guy, my wife's old GTI, and a 18-year stint with a chevy tahoe. All developed leaks sooner or later...and the BMWs were just horrendous.
I've been amazed...I thought...at the resilience of my E350 in the leak category. The cowl drains seemed so simple, and (I thought) were engineered so the drainage holes below the cowl drains were larger than the gaps in the drains themselves.
This year, after some big rain storms, I experienced the leak onto the driver's floor mat. For whatever reason, the driver's side cowl drain started to have more debris than usual, and I ended up having to clean it basically every day. This year's pollen was a sticky sort, different than years past, and I noticed it on the ground and elsewhere on my car...just a sticky mess. After a couple of big downpours, it got beyond a simple leak...now it was standing water, crazy. Also, there was something of a bathtub ring of pollen all the way around my cowl, extending across the middle and over to the passenger's side. What was also weird was that the passenger side drain didn't seem to be clogging, the pollen massing I was seeing on the driver side was not happening there.
I reached out to my regular mechanic, who I trust: "We don't do leaks"; and rather than heading to the dealership with an open wallet, I thought I'd dig into this more myself.
So I looked on this forum...inconclusive. ChatGPT wanted me to take off the windshield wiper on the drivers side and pull off the cowl cover. I got halfway thru that exercise and poured some water down and it was draining just fine. So I took my attention to the passenger side. OH. MY. GOODNESS. A couple of posts up this thread, you can see the passenger cowl drain where the sun damage on the rubber was being discussed. Net-net, the passenger drain feeds into a funnel-sort-of-thing and then below the funnel it turns inward into the HVAC system, and seems to share a drain with the HVAC system...interesting engineering. That whole drain system was plugged up with pollen, dirt, mud, pine needles etc. So ALL the drainage that was happening in the cowl area on both sides was draining thru the driver side drain.
I had to take off the battery cover, and then saw more of the integration between the two. With some light digging with long thin screwdrivers in both that funnel below the cowl drain, along with some more digging in a similarly clogged drain well below the HVAC fan, I started to make some progress. Used my dyson vac with some rigged attachments to suck out the detritus bit by bit. I ran a weedeater nylon line between the funnel and HVAC well. Slowly the flow started to get better when running pitchers of water thru it.
Ultimately, I've gotten it to the "it doesn't back up". ChatGPT wanted me to take apart the whole engine-side of the cabin filter assembly, but that looked like a job I didn't want to start. It seems to drain decently now, and given that it's taken 11 years to get to this point, I feel like I've bought myself some good time.
But my goodness, what a silly setup to run the cowl drain through the HVAC system!
There are a few ways that the drains don't work. Mine was from deteriorated rubber near the windshield allowing water to flow away from the drains into the cabin.. The BIG problem is electronic wiring in the floor under the carpet getting wet. When connectors get wet it can play games with all the components in the car. There are a few bus bars with multiple wires plugging into them. These bars direct information, like a router, to different components. When these get any corrosion they need to be replaced.
Get a low cost car cover, two pieces. Those light weight ones.
Swap and wash every week or so.
Cover your car everyday after use, so that no dirt can clog the water drain.
I cover my car even though garaged, because of ambient dust. This is for Jakarta.
When I go to my Bali villa, it has a garage but semi outdoor ( has glass roof ) and Bali has lots of bugs due to my home near padi field, car cover also helps.
============
Your description in green is wrong : But my goodness, what a silly setup to run the cowl drain through the HVAC system! The air separator box above battery is water separator for HVAC blower FRESH AIR INTAKE.
Yes, the air separator box uses the cowling for fresh air entry.
Only when car owner is so ignorant and never clean their drain water path or the plastics or foam seal have cracked and whatnot, water will not enter the HVAC blower.
Do you know how many liters of water being stuck at the water catchment plastic casing below wiper cowling for it to be able to "flood" the HVAC blower ? A LOT....
This is the water catchment + drain plastic casing below wiper cowling , mine is right hand drive car, use your imagination for Left Hand Drive car yours is.
Water catchment + drain plastic casing below wiper cowling , as installed.
The HVAC blower zone is totally isolated from the wet water zone. Thus the air-water separator above battery box is needed to deliver air to HVAC blower.
Its firewall side, the seal is for the HVAC blower fresh air intake.
Again, I am reminding : the HVAC blower fresh air intake is isolated from the wet rain water zone..............., unless plastic or seal cracked or something clogging so bad,
water level rise up so high
The air box above battery, is the air-water separator for HVAC blower air intake.
.
.
.
This is the final water drain......... at wheel well/fender. Both Left and Right side has this plastic water drain pipes
Now do you understand how much lazyness and uncleanliness + mechanical wear or damage .........have to occur, before one can flood rain water to HVAC blower intake zone......
This is pure neglect in my book, if ever my car can have rain water entering this way..........except BAD LUCK......if the front windscreen sealant failed a bit , not common but have occured.
If the flooding is up to the level I marked above in red, the air-water separator box above battery probably can not handle that much water, albeit it has its own drain too....which probably clogged too........
...............only then the HVAC blower intake get the water.
3rd reminder. HVAC blower air intake zone is totally isolated from wet water zone.
Do some teardown and learn about your car.............
END
Last edited by S-Prihadi; May 5, 2026 at 09:55 AM.
Reason: ADD INFO
So for the benefit of the group and posterity, I will share my W212 2013 E Class leak saga. I've had this car since 2015, almost 11 years now. It parks outside, on my driveway which is sloped toward the street. For a variety of reasons, I back into the parking space. We also live below sycamore trees here in Marin County, which put off an awful lot of debris. Leaves, pollen, and all manner of detritus. They are messy trees. Same house for 30 years, ultimately drain problems with all our cars, including all manner of BMWs before I became an MB guy, my wife's old GTI, and a 18-year stint with a chevy tahoe. All developed leaks sooner or later...and the BMWs were just horrendous.
I've been amazed...I thought...at the resilience of my E350 in the leak category. The cowl drains seemed so simple, and (I thought) were engineered so the drainage holes below the cowl drains were larger than the gaps in the drains themselves.
This year, after some big rain storms, I experienced the leak onto the driver's floor mat. For whatever reason, the driver's side cowl drain started to have more debris than usual, and I ended up having to clean it basically every day. This year's pollen was a sticky sort, different than years past, and I noticed it on the ground and elsewhere on my car...just a sticky mess. After a couple of big downpours, it got beyond a simple leak...now it was standing water, crazy. Also, there was something of a bathtub ring of pollen all the way around my cowl, extending across the middle and over to the passenger's side. What was also weird was that the passenger side drain didn't seem to be clogging, the pollen massing I was seeing on the driver side was not happening there.
I reached out to my regular mechanic, who I trust: "We don't do leaks"; and rather than heading to the dealership with an open wallet, I thought I'd dig into this more myself.
So I looked on this forum...inconclusive. ChatGPT wanted me to take off the windshield wiper on the drivers side and pull off the cowl cover. I got halfway thru that exercise and poured some water down and it was draining just fine. So I took my attention to the passenger side. OH. MY. GOODNESS. A couple of posts up this thread, you can see the passenger cowl drain where the sun damage on the rubber was being discussed. Net-net, the passenger drain feeds into a funnel-sort-of-thing and then below the funnel it turns inward into the HVAC system, and seems to share a drain with the HVAC system...interesting engineering. That whole drain system was plugged up with pollen, dirt, mud, pine needles etc. So ALL the drainage that was happening in the cowl area on both sides was draining thru the driver side drain.
I had to take off the battery cover, and then saw more of the integration between the two. With some light digging with long thin screwdrivers in both that funnel below the cowl drain, along with some more digging in a similarly clogged drain well below the HVAC fan, I started to make some progress. Used my dyson vac with some rigged attachments to suck out the detritus bit by bit. I ran a weedeater nylon line between the funnel and HVAC well. Slowly the flow started to get better when running pitchers of water thru it.
Ultimately, I've gotten it to the "it doesn't back up". ChatGPT wanted me to take apart the whole engine-side of the cabin filter assembly, but that looked like a job I didn't want to start. It seems to drain decently now, and given that it's taken 11 years to get to this point, I feel like I've bought myself some good time.
But my goodness, what a silly setup to run the cowl drain through the HVAC system!
Thank you for sharing this great description from Marin County, CA.
When you described how you reverse up into your driveway, I was expecting to read about TRUNK flooding issues.
Two quarts of water gets stored between rear windshield and trunk lip seal. Many chances to penetrate inside the trunk area... save some time for a chapter-II. 🤞
I have not had my share of flood issues with loose windshield and plugged up drain.
When I was cleaning my painted GND posts throughout, I did cut up an exit drain in the sticky rubber outlet in charge shuting off drain plugged.
Accessed at the rear end of both front wheels plastic wheel-well. (remove wheel, unpin plastic rivets of that big plastic wheel trim) - I'm not sure if this drain is sunroof only or cowl or both... no automotive plumber yet in my family tree.
Last edited by CaliBenzDriver; May 5, 2026 at 02:34 PM.
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