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Found out what’s causing undercarriage composite to break apart

I always wash my model 3 on my back yard and noticed that every time I back out after washing there’s a long trail of water about 50’ long right on middle of driveway. This is even after the car sitting there for hours. I looked under car and saw it dripping from rear undercarriage. I started searching online and found photos of other model 3’s with rear bumpers falling off and composite material breaking apart. I then opened my trunk and poured water around weatherstripping seal and water runs off to the sides and down but most of the water runs behind rear tail lights and and ends up inside on the rear bumper. The rear bumper has edges which act as a wall holding a lot of water. Once it fills or during driving water shoots forward drenching the composite material. This will be a big problem for many during winter when all that water on bumper freezes adding weight and stress to rear bumper.

I then drilled a small 5/16” drain hole (hole #1) on center of bumper and poured more water but a single hole was not enough and water still drained off to the composite material. I added two more holes (holes 2&3) close to the first one but no water drained from there so I ended up drilling 2 more (holes 4&5) closer to where bumper meets composite material. One of these last holes (hole #5) ended up being where it drains the best. I did kind of crappy job drilling as drill motor didn’t fit under car so I drilled at an angle. I don’t know it having those holes will hurt the aerodynamic functionality of car but at least I won’t have a bumper full of water.
 
There are 3 bolts that hold bottom of bumper and the center one is missing.


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I have big concerns about this when I noticed a gap between my trunk weather seal and the bumper (Trunk weather seal gap), thanks for demonstrating how this defect can damage your car.

I don't think the water is supposed to get inside the bumper like that, but according to the service center I talked to this is normal as all the cars they showed me had this gap. Tesla needs to address this defect by doing better sealing.
 
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I have big concerns about this when I noticed a gap between my trunk weather seal and the bumper (Trunk weather seal gap), thanks for demonstrating how this defect can damage your car.

I don't think the water is supposed to get inside the bumper like that, but according to the service center I talked to this is normal as all the cars they showed me had this gap. Tesla needs to address this defect by doing better sealing.
I had the same gap on mine and was told the same but I still had them replace my weatherstripping. This water test was done after new weatherstripping and no visible gaps but water still enters car. Weatherstripping is not the problem, water enters from behind taillights.
 
Thanks! This explains the weird dirt streaks I get and why I have a LARGE pool of water under the car after I park the car after a wash.

I haven't washed the car in a while, but it's supposed to rain in the next day or so so I'll get a chance to see what rain does.
I think this will be a bigger problem for people living in cold weather when water on bumper freezes adding weight to bumper and composite material.
 
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Reactions: Smokey4141

SMAlset

Well-Known Member
Mar 4, 2017
9,337
10,266
SF Bay Area
Great photos and videos. Hole 5 is definitely the low point in the bumper cover. Smart detective work. Also think those that have been told they drove into water filled holes in road and damaged the under carriage fabric will have a better understanding of what is going on.

Somewhere along the line there must have been a design change of parts because there were Model 3s driving thru rain, snow and icy conditions during early production and we never saw these type of issues arise.
 
Great photos and videos. Hole 5 is definitely the low point in the bumper cover. Smart detective work. Also think those that have been told they drove into water filled holes in road and damaged the under carriage fabric will have a better understanding of what is going on.

Somewhere along the line there must have been a design change of parts because there were Model 3s driving thru rain, snow and icy conditions during early production and we never saw these type of issues arise.
Yes hole #5 is the right spot just with a bigger hole, unfortunately I started on #1 and it did start draining so I did holes 2 & 3 to help out but no water drained from there.
 

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