The ins and outs of 4WD water crossings

You might think a 4WD is designed to take to water like a duck, if you believe some of the advertising.

While it’s true that most bush-capable 4x4 off-roaders are designed to have some water-fording ability, they are just as fragile as any car when their engine or electrics are exposed to too much standing water.

Some off-road water crossings are easy, some a challenge and others downright dangerous and should be avoided.

Here, we’ll take you through the basics of how to cross water without doing damage to you or your four-wheel drive.

As we’ve mentioned in other how-to stories, it is important to put together some 4WD training before heading into off-road situations like water crossings.

The practical experience you’ll get under the guidance of trained experts is invaluable.

So what is the danger when crossing water in a 4WD?

Getting bogged in a deep water crossing is bad enough, as it makes recovery difficult.

If you have driven into water too deep for the engine air intake design, the engine will take in air and potentially compression lock. Which usually means you need a tow home to get a new engine.

The worst-case scenario is that your 4x4 becomes buoyant in the deep water, then loses grip on the river bed and floats with the current downstream.

Eventually it’ll start filling with water and sink.

Such difficulties as we’ve described above are, of course, all avoidable.

Before you even leave home, it is a good idea to find out the water fording capabilities of your 4WD.

To begin with, check the water fording specs given by the manufacturer. The typical off-road-capable 4x4 should have about 500mm fording capability, with better ones around 800mm.

This should be enough to tell you any passenger vehicle 4WD – from the so-called ‘soft-roader’ genre – is not designed to drive through deep water.

Internal combustion engines are not designed to take in water into their cylinders; it doesn’t compress very well.

If the engine air intake takes in water during a deep water crossing, not only will it come to an abrupt stop, it’s likely to do severe damage to the engine, especially if it’s a diesel.

With all that in mind, one key measure for water fording is the height and position of the engine air intake.

The better standard air intake designs for water crossings source air from the inner guard or have a well-shielded upper grille intake.

The best air intake for water crossing is a snorkel, which an expensive and usually aftermarket accessory that sources intake air from a tube running up the A-pillar.

Of course, you never want to end up in this predicament, but a 4WD with a well-fitted, water-tight snorkel will probably start to float before the engine drowns.

Another option is a temporary radiator blind. The blind should be wide enough the cover the front of the vehicle and long enough underneath to reach about the front axle centre line.

While neither a snorkel nor radiator blind are likely to be necessary for a weekend away at your nearest state forest, for destinations like Cape York they become a serious consideration.

Water crossings – Quick reference do’s and don’ts:

When you have reached a water crossing, it is important to assess it before continuing.

This requires a bit of common sense. With water slowly flowing at 200mm over depth markers at a formed concrete causeway crossing and other standard 4WDs are already crossing without issue, then you’re pretty safe to proceed.

However, in other less obvious situations it’s important to stop and check out the crossing, measuring the depth and checking the condition of the bottom of the water crossing.

With some short crossings with clear water you can often work this out from the shore, but for longer ones you will have to walk across to check the depth, water current flow, any obstructions such as large rocks and how soft the bottom is.

Take your time, as it can be difficult to take in all the variations in the river bed. And don’t assume a concrete causeway will be fine – over time and during flooding, parts of the concrete can break away, leaving large hollows.

Don’t walk through a crossing if it’s in an area known for crocodiles. Getting your 4WD stuck could be the least of your worries. Find another crossing.

Before crossing even shallow water, it’s a good idea to stop anyway to allow the vehicle underbody drivetrain components to cool down.

It is not a good thing to dip components like hot axles into a cold water crossing as water may get drawn past axle and hub seals, contaminating the diff oil and ultimately damaging the diff.

If you’ve been working your 4WD hard and/or it is a hot day, there are other reasons to stop and let the vehicle cool.

You don’t want engine cooling system fans running fast when you wade though deep water as the blades will bend as the water flows across them, potentially either breaking them or flexing the fan, which may then make contact with the radiator and damage it.

Turn off the air-conditioning too, so there’s no risk of the electric fans cutting in during the crossing and doing damage.

If you find that any part of the water crossing is deeper than about half a metre, and especially if the water is also flowing fast, think about taking another route.

Before heading into water that is deeper than around the lower sill of the vehicle, make sure doors are unlocked and windows open.

That way, if the worst happens and the engine stalls and the electrics shorts out, you won’t be trapped in the vehicle.

For most crossings, you should be in low range with all traction aids engaged.

Start driving into the water, with just enough speed to ensure a gentle bow-wave around the front of the vehicle. Be particularly careful if entering water at an angle, where the nose of the 4WD dips into the water.

Dip into the water slowly then gradually increase speed. This will reduce the amount of water entering the engine bay.

Try to keep up momentum but without too much speed, as this will only force water to go where it shouldn’t.

And try to not let the engine stall, to keep water out of the exhaust.

The only time you should not try to restart a stalled vehicle is if you suspect it has taken in water through the air intake. It’s time then to inspect the intake system for potentially damaging water ingress.

If you do get stuck in a water crossing, a quick recovery with another 4x4 is the best scenario. You may need a long winch extension strap to do that, which you can buy for around $100.

Other recovery options include an electric winch, or a much slower, much more physically demanding (but much cheaper) hand winch.

Stop after a successful crossing to allow water to drain out of the chassis.

Also check under the bonnet after a deep water crossing for evidence of cooling fan contact with the radiator, or for water entry into places it shouldn’t have gone.

If you ‘re diving deep into a succession of long, deep water crossings, it’s a good idea to open transmission and diff fill plugs to see if water has found its way in.

Once water has been mixed with hot oil, it’ll turn into an emulsion that will not lubricate the gears well.

It’s cheaper and easier to drain out the mix and replace it than replace or overhaul a damaged diff.

Related:

River crossing basics