How do I diagnose my water leak? - PeachParts Mercedes-Benz Forum

shertex · #1 11-16-2011, 02:32 PM

I have water leaking into the front passenger compartment of my 92 300D, down by the feet. What is strange is that water only seems to leak in when the car moves in the rain; the last two days I have driven in the rain, water has leaked. However, there have been two other days when it has rained all day, but I have not driven the car, and water has not leaked. Does this provide any sort of clue as to where the leak might be?

Needless to say, this makes me reluctant to take it to my indie who wouldn't be able to drive around for hours in heavy rain in order to diagnose.

Thanks.

Biodiesel300TD · #2 11-16-2011, 03:18 PM

I'd start pulling out the carpets and the underdash panel to see if it's anything obvious. You might have a rust hole in the floor or in the wheel well that's allowing road spray to get in. It could also be getting drivin under the windshield seal at the bottom edge of the windshield when the car is driving. My 240 used to do that at the top edge of the windshield, it would get forced under the seal while driving and create a drip that ran down the inside of the windshield. But when sitting rain water just washed over and didn't leak. Check out the windshield seal at the bottom edge. You don't want to see any cracks, and you should have good overlap with the outisde edge of the body. Lots of times the seals shrink over time and you are left with a sliver of rubber covering the outer edge of the body. Which allows water in.

shertex · #3 11-16-2011, 03:56 PM

Quote:

Originally Posted by Biodiesel300TD

I'd start pulling out the carpets and the underdash panel to see if it's anything obvious. You might have a rust hole in the floor or in the wheel well that's allowing road spray to get in. It could also be getting drivin under the windshield seal at the bottom edge of the windshield when the car is driving. My 240 used to do that at the top edge of the windshield, it would get forced under the seal while driving and create a drip that ran down the inside of the windshield. But when sitting rain water just washed over and didn't leak. Check out the windshield seal at the bottom edge. You don't want to see any cracks, and you should have good overlap with the outisde edge of the body. Lots of times the seals shrink over time and you are left with a sliver of rubber covering the outer edge of the body. Which allows water in.

That's helpful...thanks. I have the mat pulled up as I drive around. It appears that the water begins to accumulate near where one's right foot would be....but I haven't yet detected an entrance point.

shertex · #4 11-16-2011, 08:48 PM

OK....the water doesn't seem to be coming from the front...it seems to emerging from the area immediately in front of the seat.

Ideas???

vstech · #5 11-16-2011, 08:51 PM

... in front of the seat? it could be following the plastic track that the vacuum and wiring sit in and leaking out there...
are you sure the floorpan is not compromised?

shertex · #6 11-16-2011, 09:41 PM

Quote:

Originally Posted by vstech

... in front of the seat? it could be following the plastic track that the vacuum and wiring sit in and leaking out there...
are you sure the floorpan is not compromised?

Yes, in front of the seat. Should removing that plastic track be my next step?

Anything I can see of the floorpan is not compromised.

vstech · #7 11-16-2011, 11:40 PM

as I sit here thinking on it, the driver's side cowling drain under the brake booster dumps into the body near the door hinge, and gunk buildup can cause rust to go through the floor... look under the plastic tray under the seat with a screwdriver for a hole...

shertex · #8 11-17-2011, 05:19 AM

Quote:

Originally Posted by vstech

as I sit here thinking on it, the driver's side cowling drain under the brake booster dumps into the body near the door hinge, and gunk buildup can cause rust to go through the floor... look under the plastic tray under the seat with a screwdriver for a hole...

You mean it dumps over by the PASSENGER door hinge?

Not that I know much about any of this stuff, but what confuses me is:

If it's water that's DRAINING DOWN, then why does it only enter the car when I'm driving.

If it's water that's SPLASHING UP, then why doesn't encapsulation panel (which is intact) keep the water out?

shertex · #9 11-17-2011, 10:03 AM

Oh, and I should mention: just prior to the problem occurring, I treated the area below the battery tray with POR-15. So I wonder if I accidentally blocked off a drain. Don't know whether that drain would account for where I'm seeing the water.

vstech · #10 11-17-2011, 03:01 PM

nah! driver's side/drivers side dump, passenger's side/passenger's side dump.
I was just thinking and typing...
both dump in same place.
when driving through rain A LOT MORE WATER GOES ACROSS THE CAR than when sitting still!!!

dablk1 · #11 11-18-2011, 11:37 AM

There is also a drain tube directly behind the battery area directly beneath the windshield, it' flows into a tube that's coming out of the firewall. Sometimes it gets clogged. I diagnosed that problem for a friend of mine last week. Not only was is clogged, but it wasn't even inserted into the tube. She was having the same exact issue. The water was draing behind the battery tray instead of into the tube. It seemes to have fixed the problem.

dablk1 · #12 11-18-2011, 11:43 AM

As a matter of fact, her leak was so bad that the front and rear carpet was damp. So much so that it caused corrosion on the vacuum pump that controls the door locks. The pump had to be replaced too.

shertex · #13 12-01-2011, 01:02 PM

By way of an update.... Took it to indie, confirmed that leak was NOT coming from battery compartment, but had trouble concluding with certainty the source. Based on his experience, he was "90% sure" that it was related to the windshield. So he recommend I swap out the gasket (which, while I'm at it, invovles a new windshield). BTY the indie has no financial interest in making this recommendation since it's not the kind of work he does.

So today I have it at the auto glass place, they remove the windshield and say that's not the problem. Oh well, I guess I'm happy to have a new windshield and gasket after 20 years!

They think the problem is the sunroof drains, which are draining very slowly and would certainly overflow with the heavy rains we've been having.

Waiting to hear back from my indie to see if he checked these.

Mildly frustrated, but looks like I'm on my way to resolution.

shertex · #14 12-08-2011, 04:04 PM

Looks like, while the sunroof drains were draining, they weren't draining fast enough. The auto glass place blew out the drains, and I think everthing is fine now.

A bit frustrated by the indie's misdiagnosis.....but certainly happy with my new windshield.

Zulfiqar · #15 12-08-2011, 04:46 PM

The accordion tube between the door and body where the hinges are also cause water to drain into the cabin wetting the carpet right by the feet.