Water Leak Into Cab

Clb said:

This and the cowl to hood seal...

Click to expand...

Yep, that is true too! Mine is so rotten that every time I look at it a piece falls off! Just another project!

I've already rebuilt the engine because of the cowl seal years ago. That ALWAYS gets first attention. now I need to convert to the 90's style intake horn at the hood. Mine is down low above the bumper which Ford knew afterwards was a bad idea. "Remove 'Elephant Trunk' Before Fording" is smart unless you don't know you are about to ford a river that is usually a stream.

I had the same issue on my 89, leaking windshield. A little windshield sealant worked like a charm, nothing for the last year, easy to apply

I'd guess the seal around heater box to firewall as most likely source of the leak, especially since you mentioned replacing heater core. Here's some pics of a Bull which is nearly identical. This will help illustrate "points of entry" for water. Imagine rain water gravitationally flowing down the firewall.

I just tackled my firewall leak last week with info from this thread. Couple notes:
On the OBS trucks, you can still get to the old vent access mentioned in an earlier post on the passenger side, but the drivers side is covered by the e brake bracket. If you remove the cowl cover you can snake a small shop vac hose down there and clean out both sides from the top. It definitely needs to be done.
All the seam sealant in my cowl vent was crusty, and lots of it had fallen down into the drains. I sucked it up with the shopvac. I am pretty sure that is where my leaks were coming from. I cleaned rest of sealant out, por 15ed the seams and applied 3m automotive seam sealant to the whole area.
I didn't mess with my heater box, because it was unmolested from factory at this point, and I couldn't see where any volume of water would get to past the cowl seal. I had water pouring into the passenger floorboard when driving in a rainstorm, even after replacing the windshield.

My experience with the truck was there we two leaking areas. One was present since new and was the sealant around the windshield wasn't lined up with the windshield leaving gaps on bith sides. Also the sheet metal was bent right above the drivers seat leaving a 1/4" hole. Dad gave up on it years ago and just parked it under cover. I was able to seal these gaps by removing the trim and pressing in butyl sealer. The second area was in the cowl seam where the sealer had peeled up and rusted small holes. I wire wheeled and scraped the old stuff off treated the rust and resealed the cowl. So far so good. I did get some water on the back seat recently but that may be just from wind blowing into the slider. It only happened this one storm.