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Waterproofing your FSJ

Contributed by: Dennis "Doc" Fariello


In this spiel, I will describe the methods I have come up with to successfully waterproof a vehicle (any vehicle) against the elements. None of these ideas are fancy, nor are any of them expensive. I have read about guys using compressed air, etc, but none of that here.

Basically, this will be organized into three sections. First, drive-train waterproofing. Second, basic engine waterproofing, not including ignition system. Third, ignition waterproofing, plus some easy, cheap, and functional upgrades that Jeep should have done in the first place (at least regarding the 4.2L six).

Here goes.....


Let me start by saying that, regarding the drive train, you ain't gonna keep all the water out all the time, especially on an old vehicle with leaks (read that as any Jeep...). You may think that this means your vehicle has got to be in perfect condition, but nah... this stuff will just help a LOT. But, for this system to really work well, it does make a big difference. Actually, come to think of it, yeah, your seals have GOT to be in good shape.

First, an overview of how things are as they built 'em. I guess I ought to describe the vehicles this has been used on first, so y'all don't think something's amiss when you go looking at yours, and it's totally different. This is just so that you know what I did it to, and what I started with. The beginnings may be different, but the ending should be pretty much that same regardless.

Ok, the test beasts... This was originally done to an '80 Cherokee, then later to Timex, my infamous '85 J-10. Both have (had in the case of the Cherokee, unless some poor fool is still driving it around) 4.2L (258 c.i.d.) AMC 6-cyls, T-176 trannys, NP208 transfer cases, Dana 44F front axles, and AMC 20 rear axles. Everything was the same for both, with the exception of where the vent tube for the rear axle ended up, so I won't differentiate between them, until I get to that part. Oh, and the arrangement of the vents on the transmission and transfer case were different, too. I will go into the details in the appropriate section.


The Dana 44F front axles on both vehicles came stock from the factory with rubber vent hoses running up to the top of the radiator, with flapper valves on them. I found that in REALLY deep stuff, thermal contraction would cause water to be pulled past the valve, so I replaced the flapper valve with tiny little K&N; filters. They're approx. 1 1/2 inch in diameter, and clamped right over the hoses. That was the only change needed for the front axle housing vent.

As far as hubs go, I just make sure that the o-rings are in good shape, and I haven't gotten any water at all into the hubs on Timex. On the Cherokee, I had used RTV silicone to provide some extra sealing, but water was getting in anyway. I suggest switching to synthetic grease, it seems to be much more resistant to emulsifying than standard grease. Rebuilding the hubs is also a good idea, with new gaskets and o-rings. I have been told that external hubs are much harder to keep sealed than the later model internal hubs.

If your axle seals are in good condition, then you shouldn't have any problem at all with water getting into the axle, even if you submerge the truck totally. Water CANNOT get through a properly oiled K&N; filter. However, theoretically, if you run it into a water hole up to the roof, thermal contraction of the gases/air inside the housing (especially in cold water), which is what causes the water to want to get in in the first place, may cause a seal or something to go if the vent filter is under water. Something's probably got to go somewhere. Just a bit to say that nothing is fool-proof, nor perfect. Remember, common sense prevails over all else.


Here was a difference in the two vehicles. The Cherokee had only the little flapper valves directly on top of the transmission and transfer case housings. The pickup had hoses run from each, siamesed into one tube, which turned to hard tubing, that ran up the fire wall to just behind the valve cover, where it then turned 180 degrees, so the open end was facing downward. No real problem here, I guess, but on both I ran separate hoses from the trans. and 'case to the fire wall, running up to just below the hood. Also ran them a little further to the right (passenger's) side, so as to make access to the filters a bit easier for cleaning. I also used the little K&N; filters on these hoses.


The Cherokee had the little flapper valve right on the left axle tube. The pickup had a hose running from the vent hole on the axle tube to a flapper valve located right under the bed of the truck. I replaced both with the (guess what....) rubber hose and small K&N; filters. On the Cherokee, I ran it all the way up to the roof, on the pickup, it's located just under the left-side bed rail, accessible via removing the left tail light assembly.


  • Rule one: you GOTTA have a closed PCV system.

  • Rule two: pull the zip tube off if you're gonna play in the deep stuff. (If you still have one, that is).

  • Rule three: K&N; oiled air filter element (open or stock... doesn't matter).

I also have put one of my wife's old ankle stockings over the end of the intake on the air cleaner. Keeps damn near all the water out, acts as a pre-filter, too, removing most of the gunk that gets into the zip tube. Also keeps out the bugs. Problem with it, is that you have to clean it (just hosing it out is ok) every thousand miles or so, it clogs easily, richening your fuel mixture.

Have also read that sealing the oil dipstick is a good idea, but I haven't bothered with it. I have NEVER gotten any water into my engine. There supposedly is a sealing grease available for the K&N; air filters, to provide an extra measure of insurance against water getting past it. I have used RTV, but haven't gotten ANY water past the element without running any kind of sealing agent (and I have filled the housing to withing 1/8" of the top with water on both trucks). Sucked nothing but air through that little space left over. BTW, this was of course with the zip tube disconnected, so this gives you an idea of just how deep I can and have run both these trucks.

One other thing.... seal the bottom of the air cleaner housing where it meets the carb. On the 4.2L, an oil filter gasket is a perfect fit. Yes, that's right, a new idea in recycling... next time you change your oil and filter, keep the gasket off the old filter, and use it to seal the air cleaner. Probably doesn't really matter if you clean all the oil off it first, but it's a good idea anyway.

It helps tremendously if you don't have any vacuum leaks anywhere.


This is the only part where you actually have to do anything requiring much effort, besides crawling under the truck to install the vent hoses.

Plug wires:make sure they're in good shape. I put a little bead of RTV inside the boots on both ends, plus a little bit around the joint where the boot ends and wire begins (I guess I'm kinda a belt-and-suspenders man when it comes to this).

Distributor: I have read of some pretty exotic treatments here regarding closed-cell foam and duct tape, but I have found it to not be necessary. The distributor on the 4.2L is rather low, below the spark plugs, but my system works quite well. I have never had any problem with water in the distributor, which is quite regularly totally and deeply under water. What I did was pull the cap off, and run a bead of silicone around the bottom of the cap, where it meets the distributor body. That's it. Accel and perhaps other aftermarket caps have an o-ring around the bottom of the cap, so if you have one of these, you probably don't even have to bother.

This leads into the promised improvement.... if you have a '77 and up 4.2L, switch to the Ford 8MM two-piece distributor cap. This will help with the cross-fire problem inherent to these engines. Run a little RTV around the bottom of the base cap, then also at the top, where the top piece goes on. There is a double lip on the top cap to fit over the base part, so this may not be necessary, but I do it anyway. Another advantage to the two piece caps is the flapper valve vent on them. I suppose you could modify that just like the drive-train, but I haven't bothered.


There is an old song that goes in part, "A Jeep Ain't A Submarine". I've been trying to prove this wrong since I first got the Cherokee. Hey, since it wasn't worth a damn in mud, I had to find something it could do that the big boys couldn't! Grin...

A word on cost (I knew you were wondering about this):

  • 1 tube RTV: about 5 bucks or so
  • Rubber hose: for about 8 ft. or so of it... maybe 2-3 bucks
  • K&N air cleaner: I think it was about $35.00, maybe less
  • Little filters: hmm.... 8 bucks a piece or so.
  • Two-piece Ford distributor cap: 5 bucks

So, you're looking at a total of, oh, around $80.00. Beats the hell out of a rebuild of anything.......


For the ignition, first determine if it's just wet wiring or there's water in the distributor. Either can be cured with a shot of WD-40. Wipe the cap on the inside. Easy fix.

Hubs: repack. Another easy fix.

Wheel bearings: repack. NOT an easy fix.

Engine oil, axles, rest of drive train. STOP! Let the vehicle sit for about an hour so the water and oil separate, the oil will float to the top of the water. Pull the drain plug, drain the water out. When oil starts coming out, replace the drain plug. Any little droplets of water that remain will evaporate when the unit warms back up. If you can't stop, and the oil turns green and milky, it's emulsified, and you must change it as soon as possible. It doesn't have to be immediate, you can actually wait till the end of the day to do it. Gears are pretty damn sturdy.

If you manage to suck water into the engine, past the air cleaner, DON'T RESTART THE ENGINE YET. Pull the spark plugs, crank it over to blow out the water, then re-install the plugs and go merrily on your way. I've NEVER had to do this!

You'll notice that I haven't addressed power steering or anything else. Hey, with the leaky GM boxes these beasts have, who cares? It'll drain on its own pretty quick anyway! (big grin)

  • Doc
  • Orlando, FL (the Land of the Ubiquitous Damned Billion Dollar RAT (er, mouse...)
  • '85 J-10 "Timex"
  • formerly owned '80 Cherokee
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