Water crossings

Not too fast, not too slow: This vehicle is pushing a proper bow wave through this stream crossing.

There are two unalterable facts you need to know about water:

1. It is incompressible—thus, if sucked through an air cleaner into an engine whose pistons are trying mightily to compress the contents of their cylinders by a factor of nine to one or more, it will cause Bad Things to happen.
2. It is a fair conductor of electricity—thus, if unintentionally employed to bridge the gap between the positive and negative elements of expensive electrical components—say, the circuit board of the vehicle’s CPU—it will cause Bad Things to happen. 

If these two facts make you nervous about fording rivers with your four-wheel-drive vehicle, good. Probably few things other than cats are the theme of more YouTube videos than “Water crossing gone bad.”

The easiest advice to give regarding crossing water deeper than a puddle with a four-wheel-drive vehicle is, “Don’t.” But that would ignore reality. Some water crossings are simply unavoidable, others are optional challenges to be evaluated and either accepted or avoided as part of the fun of backcountry travel. But unless you’re determined to become an impromptu video sensation, it’s smart to know a few things before you take the plunge.

Every vehicle has a critical depth above which submersion in standing water will cause those Bad Things to happen. This could either be because water will enter the air intake, or because it will reach some critical electrical component. In markets where four-wheel-drive vehicles are used more seriously for work and travel than they generally are in the U.S., it’s common for manufacturers to list the allowable fording depth of each model. For example, the world-market Ford Ranger equipped with a 3.2-liter turbodiesel and factory snorkel boasts an outstanding 800mm (31-inch) fording depth, higher than the vast majority of production 4x4s, most of which list fording depths around 20 to 24 inches. Of course any such figure is an ideal measurement, subject to intense variables in the real world, but if you can find—or determine—the figure for your own vehicle, you’ll have a place to start.

Fortunately modern four-wheel-drive trucks are in general better able to handle water crossings than those of decades ago. Back then, point-style ignition distributors were susceptible to shorting, and air cleaner intakes were open to the engine compartment and vulnerable to splashed water. Current electronic and distributorless ignitions are far more resistant to shorting, and most air intakes are now concealed inside the front fender, where little short of actual submersion is likely to result in inhaled water. On the other hand, the all-important and still-vulnerable CPU or main computer is better located in some vehicles than in others. Make it your business to find out where yours is, and locate your air intake as well. The air intake can be significantly raised by installing one of the ever-popular snorkel kits, but beware: If you plan to actually use a snorkel for deep-water crossings, the entire assembly must be diligently and completely sealed at every joint, or water will find a way in and cause . . . well, you know. And your fording depth will still be subject to the limitations of electrical components. (An aside here: Most “snorkels” fitted by vehicle manufacturers—such as, for example, those standard on Toyota Land Cruisers in markets other than the U.S.—are really just raised intakes, designed to let the engine breathe air above most road dust, and are not adequately sealed for submersion.)

Other vulnerable—though not immediately fatality inducing—components include the front and rear differentials, which can become submerged during even a fairly shallow crossing. The differential has a breather designed to allow expanding air to escape the housing as the diff heats up during normal driving, then be slowly sucked back in as it cools while parked. What happens during a crossing is the warm diff cools suddenly when submerged, the contracting air inside tries to pull more air through the breather—and gets water instead. The result is an icky sludge less than ideal for lubricating rotating parts. Fortunately many companies sell extended breather kits for most differentials, and they are easy to fabricate at home—cheap insurance even if you never need them. Still, water can also get sucked in through axle seals, so it’s smart to check your diff fluid as soon as convenient after any crossing that submerges the axles. All you have to do is loosen the drain plug enough to let a bit of the contents drip. If it's nice dark oil, you're good. If it's water or grey goo, you need to replace the fluid ASAP.

Let’s divide water crossings into two general types: with and without current. Since the latter is almost always the least fraught we’ll look at that first. 

The simplest, and most frequently encountered water obstacle is a pool submerging a section of road or trail after heavy rains. Such water is usually muddy and thus opaque, which makes it difficult to adhere to the first rule of water crossings:

1. If you can’t determine the depth of the water, don’t drive through it. (Rule number 1a is: Don’t drive around it and widen the trail, either.)

Sometimes it’s perfectly obvious that the puddle is a puddle and nothing more. At other times it’s not so obvious, such as when the pool was left after a flow across the trail, the current from which might have left ruts or a dangerously deep pocket. Turbid water also makes it difficult to determine the consistency of the bottom, which can make a big difference in how easy it is to negotiate: Compacted gravel is way better than bottomless mud. So you want to know the depth and substrate conditions before you attempt to cross, and there are two excellent ways to do this:

1. Talk a buddy into driving it first, or wait until someone else comes along and attempts it. Mostly kidding on this one.
2. Wade it.

These are really the only sure ways. But there are side benefits to stopping and assessing. Your vehicle will begin to cool down, so your diffs will have a chance to suck back in air rather than water. Also, if you have a viscous radiator fan coupling, as most vehicles do these days, it will cool down as well and unlock if it was engaged. That way if your fan is submerged it will stop rotating rather than flex forward with water pressure, possibly impacting the radiator or breaking a blade. 

If you commonly travel where water crossings are a factor, bring along a pair of sport sandals (not flip-flops, which can get sucked off) to don while reconnoitering. You want to ensure that the entry and exit points are negotiable as well as the pool itself, and if you decide there is a chance a recovery situation could arise, you’ll want to identify an anchor point for your winch if you have one.

Once you’ve decided to drive through the pool, banish all thoughts from your head of spectacular photo opportunities with flying curtains of water—that’s an excellent way to cause problems by jetting water up where its not wanted. You’ll want four-wheel-drive, low range, with all traction devices enabled. The proper speed is essentially a fast walk, to build up a small bow wave if the water is over bumper height. The bow wave leaves a trough behind it, which lowers the water level in the engine compartment. Pushing a bow wave can actually allow you to ford pools deep enough to drown the vehicle if you were to stop, so maintain a steady speed, in a low enough gear to keep the engine in the ideal part of its torque curve (higher rpm also helps keep water from entering the exhaust pipe if it is submerged). If your vehicle has manual transmission, do not shift while crossing—water between the clutch disc and flywheel will strand you in short order.  Once through you’ll want to gently ride the brake pedal for fifty yards or so to dry out the brakes; if the water is deep enough that you can see the bow wave over your hood, you should stop and raise the hood to check for water in the air cleaner and for anything else amiss.

Running water is an entirely different universe. Few people realize the magnitude of the forces that can be exerted by even a mild current. Want a comparison? Water flowing at just six mph exerts the same force per unit area as air blowing at EF5 tornado wind speeds. 

Notice how much lower the water level is behind the bow wave. Courtesy Nick Taylor

The same protocol applies for crossing a stream or river as with standing water. If you cannot determine the depth and conditions, you should not attempt to cross it. When you are wading to reconnoiter, if the depth and current is sufficient to give you any trouble maintaining your balance, it will be dangerously powerful when applied broadside to your vehicle. Since the vehicle is a lot wider than you are, walk across one way where you want the driver’s side tires to go, then cross back where the other tires will track to check the entire path for hidden holes or rocks.

When crossing moving water, you should if at all possible angle downstream. That way the current will assist your progress rather than hindering it. Crossing broadside is the next best choice; heading upstream significantly increases resistance and heightens the wave pushing up against the front of the vehicle. Just as with still water, keep the engine in its best power band and do not stop—if you do, the current will immediately begin to scour the substrate out from around your tires, quickly burying them to the frame. If the current does catch the vehicle it will usually swing the lighter rear end sideways first; if this happens correct the steering just as you would in a skid, and maintain your speed.

With non-electronically controlled turbodiesel engines and well-sealed snorkels, vehicles such as this Camel Trophy Land Rover 110 are capable of fording very deep water indeed. Courtesy Pete Sweetser/Camel Trophy Owners' Club

What if you are forced to cross a river you know is on the edge of safety? Several precautions are in order (actually these are smart for any crossing). If you have a winch, plug in the remote and run it under the windscreen wiper, over the rear-view mirror, and into the cab. (If your winch has a wireless remote, be advised that it will not work if the receiver on the winch is submerged unless it has an external antenna located high in the engine compartment.) Turn the control lever to freespool and pull out enough cable to hook to the upper part of your brush guard if you have one, then re-engage the lever. This way the hook will be easy to grab, but with the geartrain engaged there’s no possibility something can snag the line and unspool it under the vehicle. without fumbling under water for it. Have shackles, etc. close at hand, and be aware of your anchor point. If no winch is available but you are traveling with another vehicle, pre-attach a tow or kinetic recovery strap to a suitable point on the chassis, and secure it above the waterline for instant access. Discuss with your companion in advance the protocol if your vehicle dies or bogs. 

While it might seem contrary to instinct, if you have power windows they should be left down adjacent to the driver and any passengers. If the engine dies and the vehicle’s electrics fail, power windows will not operate, and your odds of being able to open doors against current are slim (nevertheless, leave the doors unlocked as well). Also contrary to instinct, clip your safety harnesses in behind you (to avoid the nannie buzzer). This is probably the only scenario when it’s better not to be belted into the vehicle, in case a rapid bail-out is necessary. If the engine does die during a deep crossing, do not attempt to restart it, as it could ingest water and turn a relatively minor problem into a very expensive one. Better to get everyone out first and arrange a recovery. How to get out? Through the windows—unless there is no other way to exit, you should leave the doors closed to keep as much water out as possible.

A radiator blind—a temporary water proof cover for the front of the vehicle—is useful on very deep crossings to help keep water and debris out of the engine compartment and air intake. This can be improvised with a folded plastic tarp or anything similar, although the Australian company MSA 4x4 makes a very stylish and effective pro version that attaches in less than a minute.

The MSA radiator blind significantly reduces the amount of water entering the engine compartment.

Safe water crossings are a simple matter of letting common sense win out over both bravado and unreasonable fear. Do it the right way—and let someone else star in the next YouTube compilation.