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Foam will cause major rust issues... it could rot out areas on the side of your dash... and vehind the panels on the fender area near the cowl.. and underneeth and the floor. And near the windshield
DONT do it.
It will be easier to find the cause of the leaks. And fix it properly.. dont ghetto things man.. ive used foam before but 9nly near my heatercore where the original foam seal had deteriorated. But id never use it near a source of water
1998 Jeep Grand Cherokee 5.9L Limited 219k
1998 Jeep Grand Cherokee 4.0 I6 laredo 430k
1990 Jeep Grand Wagoneer 155k
1976 Jeep J10.. 85k(repaired)
First clean out the vents and clear the drain hose. Rain water is supposed to go in the fresh air intake on the cowl and drain out the bottom of the vents at each side. Very common that these vents are clogged with debris that comes in the cowl vent.
It's also possible that the fresh air passage is poorly sealed to the cabin.
This is looking up under the dash of my J20 at the area above the fresh air vent at the passenger's feet. In the foreground is the sealant around the lowered air conditioning unit - just ignore that. You can see that the factory did not seal the joint between the fresh air passage and the body, and the rain water comes in there. This was repaired by cleaning the area and sealing the gap with a big bead of silicone caulk (as the factory should have done).
Spray foam is a terrible idea. Augh! All you'll do is plug the factory drain and water will pool on top of the foam. Bad idea.
Much better to seal off the cowl vent with a sheet of rubber or similar, if you must plug the vent. That will stop the rain from coming in, but you will lose the fresh air intake for the heater and defroster and floor vents.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
While you are it it and feeling industrious.
Remove the bolts holding the lower section of the front fender near the doors 2 underneath and the lower 2-3 inside the doorframe
Amazing how much crap was in mine.
Same with the inside of all my doors those stupid little screens at the bottom of the doors get clogged and they don’t drain properly
Add years of dirt pine needles, it’s a recipe for rust.
It’s just good guilty time spent with your rig
Directly above the center of the Earth
2017 Chevy Silverado DD
2016 Jeep Grand Cherokee
1987 BMW E30 325i convertible
1981 Jeep Wagoneer. 360 ,TF727 , NP208
If water is coming in from the floor vent, then the windshield gasket leaking might be the cause. Mine had a tiny dribble going into the defrost vent and down through the floor vent. It wasn't easy to see.
They do make a marine grade sprayfoam that doesn't absorb water, and I used it to ghetto plug the rot in my inner rear wheelwells. It's been there for 15+ years now. But I do not recommend using it in the air ducts.