Exhaust leak into cabin. Emergency floor pan repair. What sealer?

Ok, so I've figured out that the XJ I just bought has a pretty severe exhaust leak into the cabin. Take a look:


So, I found a couple of holes in the floor pan. One is dead above the muffler:

The other is basically right above the tailpipe:


I also found what seems to be a pretty big leak at the flange gasket. There's no question that driving the car around will make you lightheaded, and help you feel good and stupid for an hour or so after riding.
Unfortunately, I have to take this thing on a 4 hour trip to Christmas with the family this weekend. Of course, it's another 4 hours driving back.

I've recently learned that the shell itself isn't much worth saving from rust, but I've got to get this problem patched up immediately. I am going to get some sheet metal (probably 18ga) and seal up the holes that I've found. I'm also going to tear out the rest of the carpet to find any others.

What should I use in conjunction with the sheet metal to get a good seal to the pan? Will a high temp RTV sealant work well to keep exhaust fumes out? Anything better? I think I'll probably be 'painting' over the whole job with Herculiner or at least a spray in rubberized coating, but I want to try and seal the metal down at the mating surface, too. I don't have access to a welder of any sort right now, so I'll be riveting the panels down. Maybe following up with a few sheet metal screws. Any other suggestions? I understand that this is an extremely dangerous situation, and I plan to seal these holes up thoroughly.
Also, I also realize that this is just a temporary fix and will likely have to be redone down the road.

Also, I suspect that I'll have to cut the exhaust flange bolts out of place and drop new ones in. Can anyone confirm size on those? I've got 3/8'-16 from my searching.
Lastly, has anyone else had any experience with this? Any other places I should look? Could the exhaust be possibly entering through the HVAC system if I have some bad vacuum lines and the leaking flange gasket? Maybe it could come through the shifter assembly? Thank you for any help. My dog and I both appreciate it.

I'd be pretty surprised if when driving at speed any exhaust gas would be able to come in thru the floor pan. Try either blue (low temp) rtv or e6000 craft glue as a sealer. Also check your muffler for holes, because you can patch those with Thermosteel (available at wal-mart, kinda like JB weld.)

darjevon said:

I'd be pretty surprised if when driving at speed any exhaust gas would be able to come in thru the floor pan. Try either blue (low temp) rtv or e6000 craft glue as a sealer. Also check your muffler for holes, because you can patch those with Thermosteel (available at wal-mart, kinda like JB weld.)

Click to expand...

The muffler is new as of a week ago. The engine has a blowby problem, and I did notice a bit of oil seeping out of some of the weld spots on the muffler, but it shouldn't be anything bad enough to get into the cabin like it is. I'm really wondering if a lot of it isn't coming in through the windows from the flange gasket being toast. I'm not about to leave the windows up with the rust holes over the muffler and tailpipe, though.

And low temp rtv? I'd think the one over the muffler would require some sort of higher temp. Then again, there was a soaking wet plastic bag with some worthless fiberglass insulation style heat barrier practically sitting on top of the muffler.
I did a pretty decent patch job on the rust holes last night using some strips of shingle/tar paper, laid the carpet back over that, and a solid heavy weight over all of that. The post drive to work haze & daze was there this morning, so it may be coming more from another source.

Actually, after thinking about my old FS Grand Wagoneer and a 4Runner... I never had the back windows up on those things, and I never had a problem with exhaust fumes. It has to be either coming through the firewall, or if possible the HVAC. I'm still planning to patch the floor pans as well as I can, though.

Save your time n money if it's that rusty....use lots of duct tape
(50% joking):wow:

Sheet metal, self tapping sheet metal screws, and some sort of roofing tar in a can or tar cauking will do the trick.

Your muffler must be leaking too, as the emissions should only come out from the rear end.........

Don't forget to wire brush/cut out some of the loose rust if possible.

Patch up all holes.

Second Blaine. Try to cut the jagged rusty edges back to sound metal, then just apply a patch over the hole, with enough overlap. Self tapping/self drilling sheet metals screws with hex heads work great if you're using a cordless drill as a driver. I use brushable roofing tar to seal it all up and it lasts for quite a while. Put the tar on both sides if you can. It's messy and unpleasant to work with, but it sets nicely.

Silicone doesn't work very well for this application, because the rust will work under it. It seems actually to promote rust.

I've seen and worked on worse floors than that.

Cut a bigger piece of sheet metal...and use Liquid Nail Poly glue...it will be like a rock when dried. You may want to put a few self tapper screws in it to keep it tight while drying. We have repaired vehicles and used this glue to glue the entire roof on. but it can only be the Polyurethane type...and dont get it on your hands.

hope this helps
smo

My best suggestion? A couple of fire blankets, screw them down on the floor underneath the sheet metal patches. Should keep the fumes out, the heat, water etc, and the best part they'll come off clean so your later permanant work goes easier.

(IF you do weld patches later, any remaining layers of tar or adhesive are a PIB during welding prep, they are far more labour to remove than the welding itself. Any goop you smear on wont be fully cured by the time you drive it either. PEW!)

Ok. So, going on darjevon said, I started working from the front back. Actually... First I formed and cut the sheet metal to fit and then once it came time to drill through the floorpan for the rivets.... the dremel didn't want to go through.
So, after realizing that I'm going to have to get a real drill for that part, I replaced the exhaust flange gasket and re-routed some of the CCV tubing. Honestly, I think that the problem may have been the front CCV tube dumping out into the air. All the while that I was trying to take big breaths out of the window to get fresh air, I was just taking big gulps of crankcase emissions. It was basically aimed at the drivers side, so it makes sense.
After taking the grinder/wire brush to the rust areas, they are sooo much bigger. The rear passenger floorpan doesn't actually exist anymore, so it's using up the entire 24x12 sheet metal piece that I bought. I found a few more decent rust holes while pulling up the carpet, and made the decision to be rid of the carpet altogether.
The drive to work this morning was much less confusion inducing.... that's a good thing.

As far as the rust hole repair materials, sheet metal, steel rivets, some RTV that I can't remember the name of right now... copper something. Good for up to 700*. Then I'm going to seal up all of the edges with some undercoating. I'll have to decide what the plans for the car are before I drop any real money towards herculiner.

pull all the carpet, patch the holes, like above and coat everything with rhino liner, you can get it a wally world

OH also, underneath, if there's a gap between your new sheetmetal and the existing floor, use some expanding foam around the edges. Once it's dry, cut it.....then primer.......then undercoat. That's what I also did, on the underside to keep things clear.

Don't use undercoating directly on the metal or rust....use paint or primer first.

My 87 had the same problem. First time I drove it I was so lightheaded.

I cut out the old rust, riveted in new sheetmetal. Used copper rtv to seal the sheetmetal. Then spray undercoating underneath and primer on the inside. It never leaked or spread again.

87baseomatic said:

My 87 had the same problem. First time I drove it I was so lightheaded.

I cut out the old rust, riveted in new sheetmetal. Used copper rtv to seal the sheetmetal. Then spray undercoating underneath and primer on the inside. It never leaked or spread again.

Click to expand...

That's more or less exactly the plan I had. Copper RTV and all. The expanding foam is an awesome idea, though. That'll be useful for the spots in the wayback where the floor is corrugated. I doubt it's going to get done before I put it on the road this weekend, but thankfully I haven't had a problem with the exhaust since I patched up the front end stuff.