Need help finding a water leak

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gxzach

gxzach

Joined
Sep 28, 2025
Threads
1
Messages
9
Location
Los Angeles
Hey all,

I've got a 2018 Lexus GX460 that I've modded quite a bit:
BMC to fit 33s (with pinch welds flattened back)
SwitchPros in the cabin
Southern Style Offroad roof rack

to name a few that might be relevant.

I've been noticing a damp/musty smell inside the cabin after car washes the past few months but could never feel any wetness in the carpets. Well after some major rain storms this past week the smell got much worse and now I could feel dampness in the carpets.

I pulled the front carpet up and found the insulation pad underneath to be completely soaked. Water appears to be entering from front left corner underneath A pillar. See video I recorded for more details.



Would greatly appreciate any suggestions on where to look next!
 
Check sunroof drain. It likes to clog and send water straight down the A pillar and all over the wiring and modules behind the dash.

Also the sunroof seal could also be allowing water in.
 
GrizzlyClint said:
Check sunroof drain. It likes to clog and send water straight down the A pillar and all over the wiring and modules behind the dash.

Also the sunroof seal could also be allowing water in.
Click to expand...
thanks yeah I checked both forward sunroof drains are draining no problem. I thought of the seal as well but I would think I would see evidence of water stains on the ceiling fabric which I don't see any anywhere in the interior. I also looked behind the A-pillar molding above the dash and saw no evidence of water there either. Really quite puzzled here...
 
That's odd then if those are not causing it. I'm at a loss. 🤔
 
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Has windshield been replaced recently?

When you do put water in that drain do you clearly see it exiting bottom of vehicle?

I’ve had on other vehicles line detach from sunroof and still pass water down A pillar. That cover comes off pretty easy. Just remove the two bolts holding the grab handle and cover pulls off pulling directly inward
 
I agree with others, it's probably the sunroof drain. Each side has a drain. With the sunroof open, you the openings are in the front corners of the plastic pan under sunroof. You can clean them out with string trimmer line or compressed air, then verify they are clean by pouring water down them with the sunroof open. if the drains are open, the water will puddle behind the front tire on both sides of the rig.
 
If you are sure the drains are clear then the roof rack would be my next inspection point. I'd pull the A pillar cover off like Acrad said and inspect for moisture on the inside. And the headliner up front on the drivers side of course.

Over time especially if you off road the twisting and flexing of a one piece roof rack like the Southern Style Offroad roof rack will put stress on the mounting bolts which may eventually cause it to leak at the hold down bolt holes.
 
Jstawgn said:
Is your pinchweld cut and folded for tire clearance? Many cut too deep and cause body leak.
Click to expand...
Yes, looks like this:
pinchwelds.webp
 
I recently removed the roof rack as I suspected that before and resealed with RTV all around the bolts. But I would think if water ingress was from roof rack bolt holes then I would see water stains in the headliner no? Especially with a light grain fabric material up there. There is no evidence of water stain visible on the head liner anywhere.

I did check behind A-pillar, moonroof drain tube is intact and incorrect position, no evidence of moisture. Windshield has never been replaced since I've owned it at starting at 15k miles. Appears to be OEM Lexus glass.
 
Acrad said:
Has windshield been replaced recently?

When you do put water in that drain do you clearly see it exiting bottom of vehicle?

I’ve had on other vehicles line detach from sunroof and still pass water down A pillar. That cover comes off pretty easy. Just remove the two bolts holding the grab handle and cover pulls off pulling directly inward
Click to expand...
Yes I poured water directly into the drain tray and watched it exit on both sides of the vehicle underneath right behind front wheels. No evidence of moisture behind A-pillar.
 
I just went out and blasted the roof/moonroof/drivers side roof rack mounts with a garden hose for 5min and interior is still bone dry down there...
 
In that case I'd suggest checking the pinch weld flattening. Blast with a garden hose for some time and see if you get any water in. The job certainly "looks" OK but that doesn't mean there isn't a defect that's not visible with the naked eye.
 
AC Evap drain is on passenger side right? So if that was clogged I would have wet carpet on front passenger floor no? That side is completely dry.

I hit the pinch weld area with a water hose for a few minutes yesterday and got nothing. Still dry in there.

It's raining heavily for the next few days here in LA so just going to drive it normally and keep monitoring. I ended up ripping out all the jute padding under the carpet due to the mold. Going to order replacements from here and cut to fit. After I find the source of the leak of course...
 
Evap drain is on the passenger side firewall and drips down on the passenger side framerail, behind the front shock tower. I'd turn on the AC. If the line is free draining you'll have water dripping out and onto the ground. If there is no water dripping after some time with the AC on it might be plugged, although I'm not sure how water would get to the DS of the vehicle.
 
Any rubber grommets on the drive side engine bay firewall popped out and open to allow water intrusion into footwell area?
 
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