A 4WD is not an amphibious vehicle, in fact they are not even waterproof. The actual depth that you can cross depends on your vehicle. For example, a stock Blazer may be submerged at the depth a raised Toyota doesn't even wet the doorsills.

As a general rule, if its above the top of your wheels its probably too deep. A water crossing should not be attempted by inexperienced or ill-prepared 4WDrivers.

Prior to a watercrossing, it is a good idea to place your recovery gear on top of other luggage. The last thing you want to do is be searching under your cooler, tents and baggage for your recovery gear when you are stuck in the middle of a crossing.

Vehicle Preparation
The first thing to do before any unfamilar water crossing is to walk it. If you cannot walk it you cannot cross it. If the water is flowing too quickly to safely walk the crossing, then it cannot be driven across. Remember, vehicles actually float until water seeps into them. When you walk the crossing you are actually starting your vehicle preparation. You are giving the axles, diffs and gearbox time to cool down while you find out exactly how deep the water is.

Diff Breathers
When a hot axle hits cold water it cools rapidly. This has the effect of lowering the air pressure inside the axle and the diff housing, causing air to be drawn in via the diff breathers. Extending your diff breathers higher up the chassis (standard on most Landcruisers) with the aid of plastic tubing is a "must do" for regular water goers. However, it is no guarantee that water will not enter your diff. The sudden reduction in air pressure inside your diff can still cause water to be drawn in via your axle seals if the diff breathers do not equalise the pressure quick enough. This is why its still necessary to allow the vehicle time to cool down, even when extended diff breathers are fitted.

Air Intake
Water and engines do not mix very well, and when they do it almost always results in bent pistons, valves and crankshaft commonly called "hydo-locking". If you think this sounds expensive your right. The positioning of the air intake is critical to how well a vehicle can handle a crossing. For example certain Toyota  models have their air intake directly behind the headlight, which is great to allow cold air into the engine but unfortunately is equally as great in directing water into the engine (An easy fix for this is to remove the plastic tubing from the air cleaner to the headlight when crossing water).

NEVER attempt a water crossing where the water depth is above the air intake height. If you intend doing regular water crossings, its a good idea to fit a snorkel as it raises the air intake to your roofline. It doesn't mean you can use your 4WD as a submarine!

Engine Bay Protection
Placing a tarp across the front of the vehicle minimises water entering the engine bay by creating a bow wave, provided forward momentum is maintained. The result is less water for the radiator fan to spray over the ignition system, less chance of water entering the air intake and less likely for the fan to propel its way upto and through the radiator.

Diesel vehicles are usually better for water crossings as you do not have the ignition system to worry about. Water in the ignition system usually results in a stalled engine and not actual engine damage, though this is of little comfort when you find yourself stuck in the middle of a crossing. Depending on the water depth, its advisable to climb out of your window rather than open the door and flood your carpets. To minimise stalling from a wet ignition, it’s a good idea to spray all the ignition system with water repellent beforehand.

Radiator Fan
While under the hood spraying water repellent, check to see what type of radiator fan is fitted. Most 4WD's these days have the viscous coupling type, which means that when the engine is cool enough the fan doesn't spin at full speed. With the engine off, try and turn the fan. If it turns easily, you will probably get away without having to take off the fan belt. If it doesn't turn easily or yours is the fixed type, then you should remove the fan belt, If you don't and water enters the engine bay, the fan may act as a propeller, bend forward and cut a nice round hole through your radiator. It’s certainly one problem you don't want to discover once you have completed the crossing. Even if it doesn't affect your radiator, you still do not want water being sprayed around, especially in a petrol vehicle.

Walking the Crossing
When walking your water crossings its best to walk in the intended wheel tracks to find if there are any hidden rocks or potholes, as well as for checking the depth. Potholes at common crossings are often caused by previous vehicles spinning their wheels after hitting a submerged rock. So if you find a pothole, check for submerged rocks. It’s a good idea to place markers at these points so you can avoid them. Its been known for a vehicle attempting a relatively easy crossing to suck in water when a single pothole has caused the hood to momentarily dip below the water level, causing water to enter the air intake, resulting in hydro-lock and a damaged engine.

Driving Technique
With a mental picture of your route, or better still, with markers in place, and all your vehicle preparation done, its time to start the crossing. Before you enter the water, remember to take off your seat belt and wind down your window.

Using low range second gear at 1500-2000 rpm (for most vehicles) creates just the right bow wave. Its important to get the speed just right as too fast will send water everywhere while too slow may flood the engine bay. Hopefully you follow your markers and get to the other side with no problems. But if you do strike problems avoid using the clutch as this may allow water to get between the friction plate and the flywheel, resulting in limited drive.

If the wheels start to slip, its important not to over-rev the engine but back-off the accelerator and hope the wheels regain traction. Excessive wheel-spin will not help.

If the engine stalls, put the vehicle in neutral without using the clutch and attempt to restart. If luck is on your side the engine will fire up. Now is not a good time to wish you had already disconnected the fan belt, as your engine bay will be flooded. Its normally best to use 1st gear low range and with a minimum of clutch usage, try and extricate yourself from this predicament.

Maintenance after Water-crossings
So once you have successfully crossed to the other side and are on your way home, you don't need to give the water crossing a second thought, right? Wrong! Any crossing at axle depth or deeper necessitates a checking of the diff oil for water contamination. Having an extended diff breather is not a 100% guarantee of waterproofness and any crossing above your axles without extended cliff breathers should mean a mandatory inspection.

Checking your diffs for water contamination is very easy. Since water is heavier than oil, it will collect at the lowest point in the diff, right where the drain plug is located. After allowing time for your vehicle to cool, just loosen the drain bolt and run a small amount (~20mls) of the diff oil into a glass. If you're unlucky enough to have water present, the diff oil should be drained. It is best to flush the diff several times to ensure all traces of water are removed. Milky coloured oil also indicates water is present and should also be changed.

If you're like the majority of 4WDrivers, you won't be able to change the diff oil until you get home, because you won't have spare oil and a sump pump to change it. If you suspect contaminated oil (a deep water crossing without extended diff breathers or perhaps you have leaking diff seals) then you can try and remove the water by draining the diff until only oil comes out the drain hole. Do not drain too much and leave your diff short of lubrication. Collect this oil and water emulsion as you should never dispose of oil into the environment. Save it till you get back home and dispose of it properly.

Its not only diffs than con have water contamination, but also your gearbox, transfer case and engine oil. However, it is usually only when a vehicle is stationary in deep water that these components are contaminated.

Amongst other items to check are bar mounted electric winches. These components may not be used for extended periods and when they're needed you may find they have seized up. If the winch has been submerged in water it is advisable to strip it and grease it accordingly. A quick operation of it after a crossing may prove it still works, but you may find out when it seizes that you washed all the grease out 6 months ago!

A water crossing is something that should not be taken too lightly as it has the potential to do expensive engine and drive-train damage. However, with the right vehicle preparation and post crossing maintenance, you can enjoy some of the most challenging 4WDriving around.

Watercrossing Summary
Vehicle Preparation

• Walk the crossing to check its depth.
• Don't cross fast flowing water.
• Place markers at hidden obstacles.
• Place a tarp across the front of the vehicle.
• Disconnect the fan belt if a viscous coupling fan is not fitted.
• Spray water repellent on distributor and ignition wires.
• Pack recovery gear on top, ready for use.

Driving Technique

• Take off seat belt and wind down window.
• Use low range 2nd gear (in most situations).
• Drive at a steady speed to create a bow wave.
• Avoid using the clutch.
• Do not over-rev engine if you lose traction.
• If engine stalls, place in neutral without using clutch to restart. Takeoff in 1st low.

Post Watercrossing maintenance

• Check diffs etc for water if depth above axles.
• Check winches if fitted.