Driveline If you've got a leaky seal somewhere on your driveline, you CANNOT expect that seal to keep water out of the driveline if it cannot even hold back gear oil. All the seals on your vehicle need to be in good shape. If you have a significant number of miles on your seals and are trying to waterproof your vehicle, you'll need to replace all those old seals.
Axles
Waterproofing the driveline will vary a bit depending on how your vehicle came from the factory. Jeep TJs for example come from the factory with extended breathers already on the axles. Other vehicles, such as my 88 4Runner, came with a breather right on the axle housing, and only a cap to help keep water and debris out.
Transmission & Transfer case Just as your axles have breathers, your transmission and transfer case will also have breathers. You'll need to inspect your cases and see what the breathers are like, and come up with a plan to extend the point from which they breathe.
My Toyota transmission and transfer case had breathers similar to those found on the axles, but the breathers were built into the cases, rather than a removable piece as on the axles. My choices were either to drill and tap the cases to accept a fitting like I used on my axles, or to remove the cap from the breather, and attach my hose to the stub of the breather that was left. The thought of drilling and tapping my recently rebuilt transmission didn't appeal to me, so I opted to attach the hoses as best I could to what was left of the breather.
Water & Oil Don't Mix If you get water in with your gear oil, you NEED to get it out. If you choose not to change your gear oil and continue to drive on it for many miles your will most likely burn up your gears. Paying a few dollars for a gallon of gear oil is many times cheaper than paying for new ring and pinion after you toast your gears.
I've read before that if you let your truck sit, the gear oil will have a chance to rise to the top and you can pull the drain plug and let most of the water out. Don't believe it. Good old 90 weight is heavier than water, and the water will rise to the top. The only way to get the water is to completely drain and refill the case. If your vehicle uses a lighter oil, it may be true that the oil would rise to the top, but I wouldn't be willing to bet my ring and pinion on it.
Engine Fan vs. your radiator Engine fans are designed to pull air through your radiator. What happens when you're crossing a stream and your fan blades begin to cut through the water? Because water is heavier than air the fan blades flex or bend towards the radiator. Depending on their distance to the radiator, and the stiffness of the fan blades (or type of fan) the blades may actually be forced into the radiator, bending fins and possibly breaking a core tube. Both are a serious problem if you're wheeling far from civilization in the heat of summer.
One solution is to make a metal ring out of sheet metal and attach it to your radiator. The ring will not significantly reduce the air flowing through your radiator, but it could prevent damage should the blades be pulled into the radiator during a water crossing. The ring will work like a skid plate, allowing the blades to slide along the ring without doing damage to the core tubes.
Some would argue that a better solution is an electric fan. Electric fans can provide as much or more air flow through your radiator as a stock fan, but there are some things you can do with an electric fan that just isn't possible with a belt-driven fan. The Flex-a-lite fan I installed in my Toyota I wired with an in-cab switch so that I can cut the power to the fan when I am crossing deep water. This eliminates all chance of doing damage to your fan or your radiator.
Engine If you've got a leaky seal somewhere on your engine, you CANNOT expect that seal to keep water out if it cannot even hold back engine oil. All the seals on your vehicle need to be in good shape. If you have a significant number of miles on your seals and are trying to waterproof your vehicle, you'll need to replace all those old seals.
Dipstick
I thought it would be nice to start with something easy. Every dipstick I've seen has had a rubber seal on it to help keep oil in and debris out. Most the time the dipsticks seal just fine (Chevy's problem with their auto transmissions spitting out their dipsticks a few years back is suddenly coming to mind) and there is no need for any improvement before safely submerging the dipstick. If your dipstick leaks or it will simply make you feel better, take 30 seconds and put some electrical tape around the dipstick to seal it up.
Distributer Cap: Here it wouldn't hurt to do a little background checking on your vehicle's distributor cap. Toyota caps are not known for having a problem with water getting into them. I did not seal my distributor cap in any special manner. An easy measure of precaution is to remove the distributor cap, run a bead of silicone around the edge of the cap, and reinstall. My 4Runner also has a splash guard over the distributor cap that came with a factory 'cold weather package.'
Air Intake Without a doubt the quickest way to do the most amount of damage to your engine is to suck water in through your air intake. Water does not compress as air does. If water is sucked all the way down into a cylinder the intake valve closes and the piston comes up on its compression stroke, the piston will try to compress the water, which is not possible. The list of parts that could or will break is a long one, but one of the most common is a hole blown through your engine block, or simply a cracked block.
Many times water is sucked into the engine, and the engine stalls before damage (or significant damage) occurs. If you do not attempt to start the engine, the water can be removed later, and the engine may be saved. If you choose to crank over the engine you've chosen to destroy it. I'll talk about how to remove water from your engine later in this article.
The best preventive modification you can make to your intake for water crossing is the addition of a snorkel. Snorkels simply raise the point at which your vehicle draws in air, similar to extending the breathers as we talked about last month. Snorkels come in many flavors ranging from home-brew to bolt-on manufactured units.
A good example of a home-brew unit is this snorkel created by Allen Jensen. It is made from PVC pieces purchased from a hardware store. This snorkel draws air from the back of the engine compartment, rather than right behind the headlight. Overall it draws air from a point several inches above the stock location.
I have the Safari Snorkel (available from ARB) installed on my 88 4Runner. This is an external snorkel that goes through your fender and up the A-pillar of the windshield. It is the ultimate in intakes for deep water crossing, drawing air at the highest level of the vehicle, the roof. With this snorkel you know EXACTLY what the water level is compared to your intake, because you can look out your windshield and see it.
Electrical While its true that water in most of the electrical connectors on your truck will not stop you in your tracks, that not true for all of the components. Water in your trucks computer (if your engine has one) has a very good chance of stopping you right where you are. If water does get into an electrical component and does no immediate damage there is still the risk of the water corroding the electrical contacts, creating problems for you many miles later.
Spark Plug Wires/Ignition Wire: Spark plug wires and your ignition wire are extremely easy to water proof. Take a tooth pick and some silicone caulk. Use the tooth pick to carefully smear the silicone around the inside of the rubber boot. Take care not to coat the metal contact. The other end of the wires where they attach to the distributor cap and the ignition wire should get the same treatment.
Electrical Connectors Every electrical connector I found beneath the hood of my 88 4Runner was water tight from the factory. The back of each connector is water-tight and the mating end has a rubber O-ring built into to keep the elements out. As an extra measure of protection I took my tooth pick and added a bit of silicone to ensure it seals tight.
Then there is the connector on the back of my PIAA lights. I was disappointed to find the connector is not even remotely water-tight. Using silicone caulk I sealed the mating surface, and filled the back of the connector where the wires enter it. This should prevent water from getting to the contacts and corroding them.
Engine Computer I have always been told that the computer in Toyota trucks is reasonably water-tight. When I pulled the kick panel and took a look at my own computer I was SHOCKED that is was not even remotely water-tight. There were gaps several millimeters wide where water would seep right through. The electrical connectors were not of the sealed variety either. You will need to find the computer on your own truck and see how water-tight it is for yourself.
Apparently Toyota never thought their vehicle might someday be driving around with a couple inches of water in the cab… not one of their US models anyway! While I don't look forward to having water in my cab I realize it is a distinct possibility, and will prepare the computer appropriately. Once again using silicone caulk I sealed every nook and cranny in that computer case until I was sure I could submerge it and it would take on no water. I reinserted the connectors with plenty of silicone around the edges, and filled the back of the connectors where the wires enter the connector.
Body It is unreasonable to expect the body of your vehicle to prevent all water from getting into the cab. Bodies are simply not that water-tight. If you're going to be in deep water for more than a few seconds, you must expect to have some water in the cab with you. You can take steps to minimize the amount of water getting into your cab.
Make sure all drain plugs (if your vehicle is equipped with them) are in place. Silicone the rubber boot around your stick shift if you have a manual transmission. Make sure your door seals and rear tailgate/hatch seals (if applicable) are all in acceptable shape. If you have put any holes through your firewall to wire in your accessories, make sure they are sealed with silicone. These steps will help to minimize the amount of water your vehicle takes on.
If you go too Deep: Accidents happen. If you have no snorkel, chances are one day you may go too deep and stall the engine. What do you do?
DON'T CRANK THE ENGINE OVER!!!!! The natural thing to do when you stall your engine is to start it right back up. Don't do it! If water did get all the way into your engine you're almost guaranteeing damage if you crank the engine over.
You must have the vehicle towed or winched from the water. Once its out and on level ground so you can work easily, remove all the air intake hoses that carry water to your carb or throttle body and drain them of water. Leave them off the vehicle for now.
Next pull all of the spark plugs. Once they are removed, crank the engine over for a few seconds. If you had water in your engine you will see it shoot out of the spark plug holes. Replace the plugs, and plug wires. You can now say a little prayer to yourself and try cranking over your engine.
You may have to crank for some time to push any water out that may have filled your exhaust line after you stalled. With any luck your engine should start up… but don't expect it to run too smoothly at first. There is still a lot of water in your exhaust line.
Hopefully this will get you back to civilization, where you should change your engine oil at the first opportunity you have.
This concludes our discussion of deep water crossing preparation. I hope you have found the ideas presented here useful. Happy snorkeling to ya!
http://www.off-road.com/toyota/tech/water_crossing/index2.htm