My cab leak locations

[NC Tom]

The baby powder trick worked great!!! Now I need to pinpoint the leaks for repair.

 

Driver side had one up under the foam pad behind the pedals. It's likely coming from the firewall, correct?

Also, Driver side had water on the door speaker grill as well as the floor. There is a small gap between the vent and main windows. Maybe leak is there?

Last leak on driver side I think is coming in from the top of the door frame.  don't know if the seal is bad or the door frame is bent or both. Water will come in through there if run through a car wash.

 

The passenger side leak is also firewall, I think. Before the rain came through, I took off the antenna and coated the plastic parts with flex seal. Thinking that and potential leaks from there would be solved.

 

Then there is the back window. Are the seals around the window the only areas water will leak? Is that repaired only with a new gasket?

 

 

[Muncher]

Passanger side good chance that the antenna boot is leaking almost all of mine leaked there i always just seal it with seam sealer 

[87MJTIM]

I am getting water on the passenger side during some rain storms. It appears to come through the heater vent box. I have seen videos on YouTube about leaks coming through the front cowl. The water drips through a metal seam where the sealer has dried and cracked. The videos show cutting an opening in the cowl’s metal to access the sealer seam. Then reapply caulk or RTV to seal the leak. I not sure I would want to use these extremes on my MJ. 

[Pete M]

that's a lot of leaks.  

 

any water that enters the door should drain right out the bottom.  window wipes are never perfect seals.  my guess is that leak is dripping around the door and bottoming out right there so it comes in. 

 

based on what I found in Breanne's truck, I'd suggest pulling the dash and doing it all properly.  it sucks, but is worth it for the access.  rear window likely needs to be pulled and re-glued.  for the cowl, I pulled off the hood and sprayed flex seal through a straw to get it all around. seems to have worked. 

[87MJTIM]

3 hours ago, Pete M said:

for the cowl, I pulled off the hood and sprayed flex seal through a straw to get it all around. seems to have worked. 

How did you do this?

 

These are some of the YT videos I watched.

 

 

 

[Pete M]

the hood hinge hole is your sole access point (without cutting).  I vacuumed through a rubber hose, blew it with compressed air, stuck a tooth brush in and scrubbed around as best I could, repeat.  then sprayed the sealant through a small piece of tubing to get it all over the place.  it wasn't pretty, but there's no way I was cutting an access point for that truck.  this was good enough (and seems to have worked).  there's sheetmetal bits in there that makes this extra fun.

 

 

[NC Tom]

On 9/10/2026 at 7:56 AM, Muncher said:

Passanger side good chance that the antenna boot is leaking almost all of mine leaked there i always just seal it with seam sealer 

I sealed that from the exterior. I guess I need to crawl up under the dash.

[NC Tom]

On 9/10/2026 at 11:09 PM, Pete M said:

the hood hinge hole is your sole access point (without cutting).  I vacuumed through a rubber hose, blew it with compressed air, stuck a tooth brush in and scrubbed around as best I could, repeat.  then sprayed the sealant through a small piece of tubing to get it all over the place.  it wasn't pretty, but there's no way I was cutting an access point for that truck.  this was good enough (and seems to have worked).  there's sheetmetal bits in there that makes this extra fun.

 

 

Oh boy. That sounds fun.

[NC Tom]

On 9/10/2026 at 5:56 PM, Pete M said:

I'd suggest pulling the dash and doing it all properly.

 

Oh no. Not that! Guess I'll check the "How-to" section.

[Pete M]

it's not for the feint of heart, but there's no way to be more thorough with a truck you plan to keep.    there are a bunch of youtube vids too.  plan on replacing things too like the ancient heater core. and various gaskets.  do all you can while in there.  AC complicates life. 

[Gjeep]

In addition to what you have noticed, you'll also want to POR15 the entire floorboard. The seams aren't fully sealed. Rainy season water can also come up from between the floor panels and seat track mounting studs. When you POR15 it, you'll get to see all the less than sealed spots. Worth doing before putting the interior back in.

[NC Tom]

2 hours ago, Gjeep said:

In addition to what you have noticed, you'll also want to POR15 the entire floorboard. The seams aren't fully sealed. Rainy season water can also come up from between the floor panels and seat track mounting studs. When you POR15 it, you'll get to see all the less than sealed spots. Worth doing before putting the interior back in.

I know. I ran out and need to get some more sealer for that.

[ghetdjc320]

I’ll definitely echo the above regarding por15. Get it everywhere you can on the back side of joints. 
 

For the back window, that one can be a genuine pain. It could just be that you have some seal failures (it’s urethaned in place). But, the cab corner seams near the bottom corners of the window are also terrible leak spots. On my last MJ I had to cutout and repair the seam with new metal due to hidden rust. You may be able to get away with some por15 there as well. But the source tends to be the corners of the window frame in the cab. The factory seam sealer shrinks and leaves open gaps where water finds its way into those pinch seams. Pulling the rear window is a good idea. Personally, I’d have it professionally removed then replaced since the trim can be difficult to remove intact. 

[NickyV]

I recently had the entire dashboard and HVAC box out (working on adding A/C). While it was out, I did something similar to @Pete M. With rubber gloves on, I reached through the fresh air hole and spread black RTV around the base of the water dam thing that's supposed to channel water around and out the side. I also used the black RTV on any hole I could find going between the cab and outside. Put grommets in the holes where the HVAC box mounts to the firewall and RTV'd both sides. Pulled the fuse box, cleaned it and when putting it back in, I RTV'd the gasket. RTV all over the antenna plug, etc... I tested by running water through cowl channel. Think I did a pretty good job.

 

But I think what might actually make the biggest difference is I drilled a hole through the top of the wheel well, right underneath where the blower goes. When it rains, water pools up against the blower motor seal. Any tiny imperfection at the base of that seal and it's going to get through... unless it has a place to go.

[NC Tom]

On 9/16/2026 at 3:08 AM, ghetdjc320 said:

You may be able to get away with some por15 there as well.

I'll try that.

[NC Tom]

On 9/18/2026 at 12:48 PM, NickyV said:

 

 

But I think what might actually make the biggest difference is I drilled a hole through the top of the wheel well, right underneath where the blower goes. When it rains, water pools up against the blower motor seal. Any tiny imperfection at the base of that seal and it's going to get through... unless it has a place to go.

Interesting.