Water membrane

docron · Jul 6, 2026

I think I'm going to have to cut another membrane learning a few things.
My additional plan is to lay a bead of clear silicon adhesive along the underside of sill of the grille effectively creating a waterproof barrier from water draining in the slots and only being directed to the drainage channels.

Bond_42 · Jul 6, 2026

I replaced the OEM cracked and torn one with a better bigger version like others have done. Then I took off the lower windshield moldings and made a small eyebrow kinda shape out of another piece.. laid it on the top rail that the lower windshield molding then clips/screws onto. It holds it perfect in place. Water will run down it way past the fuse box/ac box. Pics attached. Hopefully makes sense.

silent cilantro · Jul 6, 2026

@Kimmax will your improved water membrane go this far up?

Kimmax · Jul 7, 2026

silent cilantro said:
@Kimmax will your improved water membrane go this far up?

I’ll try to make it possible to install like this but not mandatory

Beachbum · Jul 7, 2026

Is the outcome of Docrons testing, that the Lotus membrane actually does not resolve the issue, as the water gets top the fuse box, through the clip holes and the membrane is after that point?

cst · Jul 7, 2026

U guys are pouring water down the windshield to simulate rain but your assuming your never going to drive thru a huge rain storm? What about when the detailer is using a pressure washer?
The water will over flow the lip of the plastic trim and go thru the gills and over into into the frunk panels.

When I washed my car I shot the water all over the windshield and down hard on purpose, then opened the hood.
I then took off the panels and there is water all over the OEM membrane. Alot of the water was coming thru the center hood latch attachment in front of the rubber bumper. There are screw holes for the metal parts that are open.
The way the OEM membrane is folded kept the water channeling away from the driver's side.....I could see that the resistor pack was dry. However the water was dripping down the other side onto the wiring loom...... surprisingly the fuse box pretty dry.

You can't account for every water ingress but these are some things to consider before u squirt silicone all over the place....
Bond_42 looks like he's close to a possible "solution" but I don't want to remove the whole windshield trim and wipers...I always break something.

docron · Jul 7, 2026

cst said:
U guys are pouring water down the windshield to simulate rain but your assuming your never going to drive thru a huge rain storm? What about when the detailer is using a pressure washer?
The water will over flow the lip of the plastic trim and go thru the gills and over into into the frunk panels.

When I washed my car I shot the water all over the windshield and down hard on purpose, then opened the hood.
I then took off the panels and there is water all over the OEM membrane. Alot of the water was coming thru the center hood latch attachment in front of the rubber bumper. There are screw holes for the metal parts that are open.
The way the OEM membrane is folded kept the water channeling away from the driver's side.....I could see that the resistor pack was dry. However the water was dripping down the other side onto the wiring loom...... surprisingly the fuse box pretty dry.

You can't account for every water ingress but these are some things to consider before u squirt silicone all over the place.

technically, I am not squirting silicone ALL over the place, just on the sill of cowl.

But the slots are now a known vulnerability

cst · Jul 7, 2026

docron said:
technically, I am not squirting silicone ALL over the place, just on the sill of cowl.

But the slots are now a known vulnerability

Well if your gonna try the silicone put some to close up the gaps around the blue arrows and anything else in those areas and let me know if it works.

cst · Jul 7, 2026

Actually how essential is the slots? What if the bottom half is sealed with a rubber membrane around the about a foot to each side of the middle?

Eagle7 · Jul 7, 2026

docron said:
technically, I am not squirting silicone ALL over the place, just on the sill of cowl.

But the slots are now a known vulnerability

I checked on my own car and my fingernail does fit underneath the edge of that long vented plastic piece, so standing water would be able to work its way under it. I think I'll seal mine too.

Eagle7 · Jul 7, 2026

cst said:
Actually how essential is the slots? What if the bottom half is sealed with a rubber membrane around the about a foot to each side of the middle?

I've always thought the slots were more for heat ventilation rather than water. When you stop the car, all the radiator heat has to go somewhere. I thought those were for ventilation.

Foosh · Jul 7, 2026

@cst lives close to me and we were acquainted though our local Porsche club. He offered to install his solution to my car, and he did a 2.0 version with silicone (purchased from Home Depot), based upon his experience designing and installing the new membrane for his car.

The depressions seen in the photo below are angled to channel water away from all the vulnerable components which are now covered. The factory membrane was left in place per the guidance from our local dealer. Zip ties are visible and used to keep the cover from falling down at the top.

cst · Jul 7, 2026

Eagle7 said:
I've always thought the slots were more for heat ventilation rather than water. When you stop the car, all the radiator heat has to go somewhere. I thought those were for ventilation.i

I figured as much...but if we were to add a 2inch membrane along the base to about halfway up the slots about 3 feet spread....to help divert the water away from the center....you would still have air flow and block excessive water doing down the center towards any holes.

I think an overlapping layers of protection can only help....I'm just throwing ideas out

cst · Jul 7, 2026

Picture a rubber 2 inch blade like a windshield wiper covering the bottom 3rd of the slots to prevent water over flow going into the wiper nozzle and center latch holes.....layers of protection...I borrowed this pic

OliverB · Jul 10, 2026

Nice…

My carpet is drenched lol.

OliverB · Jul 13, 2026

Nelumbo said:
No, I understand that you were joking. I think my dealer is great, but I am actually concerned that if I take my car in to have them look at the HVAC, they may need to hook up to the OBD II port to monitor and will find the JB4 there. I took delivery of my car in December 2024 and started having the classic symptoms recently. I loved Blackthought_'s DIY membrane and wanted to emulate it, so I decided to take a look at my membrane and sure enough it was bunched up, creased, cracked, pooling and leaking. I got the membrane out and tried to gain access to the plug but ultimately decided to have the dealer honor their warranty. I buttoned everything back up without the failed membrane, which I hope they will not take issue with. Perhaps I should just unplug the JB4 and tuck it away out of sight. That won't erase any suspicious data logging history which may appear, though.

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Your membrane has the same crease/rip, towards the rear, as mine. My car is at the dealership right now regarding the water ingress I posted a few days ago.

The probable scenario is that water pools up towards the rear and pours directly over the HVAC box when the membrane inevitably fails. There are gaskets made out of foam on that box and they are not 100% waterproof.

I’ve had an HVAC failure a few months ago and this is most likely correlated to the membrane.

I’m starting to think that the only solution is to have a membrane that is seated between the windshield and the shroud to avoid any kind of folds.

Nelumbo · Jul 13, 2026

OliverB said:
Your membrane has the same crease/rip, towards the rear, as mine. My car is at the dealership right now regarding the water ingress I posted a few days ago.

The probable scenario is that water pools up towards the rear and pours directly over the HVAC box when the membrane inevitably fails. There are gaskets made out of foam on that box and they are not 100% waterproof.

I’ve had an HVAC failure a few months ago and this is most likely correlated to the membrane.

I’m starting to think that the only solution is to have a membrane that is seated between the windshield and the shroud to avoid any kind of folds.

I have had these results for while now, but I was so stunned by the . . . lack of service results . . . that I was unsure as to how to update the group. Here it is now:

I got my car back, and the service notes state, "Could not duplicate customer state, tried a couple times and the blower motor speed seems to work okay. Compared to same year model. Checked for TSB, none for this concern. Checked water sheild(sic) is okay and no cracks." Apparently, clearly obvious cracks and failures in the membrane were too subtle to observe.

The technician did find a CCM software update that was performed along with a VCM update. Apparently, my fear of them raising warranty issues about my JB4, 3rd cat delete, and Eventuri were unfounded. However, when I realized that they didn't even look at the membrane, I "confessed" that I had already R&R. I showed pics of the cracked membrane in situ and spread out on the garage floor to my service manager. He did not appear concerned that I had already explored potential causes. He requested that I send him the pics to show to the service tech which I did, via email. I don't know of any consequences. At this point I will just monitor the AC and see if just the VCM update has fixed the problem. I will also install a full width membrane made of better material and drainage tubes similar to what others have already done here.