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C216 water drains blocked

Riva811

MB Enthusiast
Joined
Jan 7, 2018
Messages
1,054
Location
London
Car
CL500 Blueefficiency
Hello I am suspecting my water drains on the left side are blocked as I noticed the following:
  • Foggy windshield at the left side even when the car is off
  • Foggy windshield when driving
  • AGW (which probably needs replacing now) stops working when it rains
  • Ambient temperature sensor is playing up after a recent visit to a car wash
So how do I check and how do i unblock them?
 
On the AMG CL version (yours must be similar) there are 4 drains which can get blocked in the bulkhead area causing water ingress. On the drivers side there is a drain to the bonnet grille, with a large star shaped bung visible when you open the bonnet. Open up the bung, you'll be able to feel if blocked. In the middle of the windscreen scuttle between the wipers there are a row of drain holes - these seem to get blocked easily from debris from the screen. A leaf can block them also. Make sure these holes are clear.
On the passenger side you need to look into the plastic grille on the bulkhead. If full of water you need to unclip and remove the grille, there is a rubber drain hole at the bottom, which you need to poke open with something like a skewer to drain the water. However,the worst culprit for blocking is the drain adjacent to the passenger side bonnet hinge. Follow the wiper scuttle to the passenger side- there are 4 square holes which also block check these are clear, wipe away debris. These 4 square holes drain water from the scuttle into a plastic open drain fitting right by the bonnet hinge. This is the problem area, because the drain tube has a 90 degree bend about an inch or so from the opening and blocks easily. You will need to poke something flexible down this to clear it. I used curtain wire. Use a large syringe or something similar to flush.
 
Thanks for that I will give it a go. Looks like the same applies to w221, I discovered a screenshot of the Mercedes diagnostic indicating the four drains you mentioned in addition to some pipes going around the sunroof but it wasn't clear how to unblock those.
So if the water is at the front, hopefully this means it's an electrical shortage at the front which causes agw to go stupid. This theory is reinforced by an instance where my battery drained after a car wash.

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Hope you get it sorted. Certainly our 216 is the worst car I've ever had for misting up. It's totally leak free and I've put the problem down to the car being so air tight and insulated. I would check to see if the passenger side carpet is damp, look under it if necessary. This seems to be the most common area where leaks due to blocked drains come to light on these models.
 
I was able to unclog the drains going down the left and right sides of the car. The passenger side is a bit tricky as it has an angle or two. The driver side looks like a straight line down. The centre drains appeared to be ok, the are not accessible directly but the drain water via the wiper fittings.
Need to figure out the sunroof next
 

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The previous diagrams are for a W221, looks slightly different for a C216
B78045000059.071115.png
 
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My front windows stopped going misty since i unclogged the front drains. However, when it rains i lose sound and in one instance the rear parking sensors sounded like they were underwater. I recently opened up the rear left panel to check if the amplifier is wet but it seems intact. So my suspicion is that water somehow gets into the back of the car were the rear parking sensors and the subwoofer are located. I cannot see any water on the paneling of the car but the rear window gets misty so I am just trying to figure out where does the water gets stuck?
I will pass a soft cable from the sunroof drain just in case but I am unsure about subwoofer/parking sensors. Any thoughts?
 
I took my CL to the Mercedes dealer they unblocked all the drains FOC
 

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