River crossings are one of those things that can make or break a 4WD adventure. If you get it right, you can access areas that others seldom go. But if you stuff it up, you can ruin your car, your camping gear and your holiday. So before you attempt to go charging through a raging river in your prized 4x4, it’s imperative you have a clear understanding of everything you need to consider to get to the other side.
The maximum depth for your vehicle
“The first thing to do is to find out how deep your vehicle can go. There are two heights you have to contend with to determine this. One is the air intake height and one is the exhaust manifold height,” says 4WD expert and owner of SafeTrek 4WD Services Jim Kennedy.
The exhaust manifold height is important because if the water is above this height and you turn your vehicle off, the water will run back up the exhaust pipe, through any open exhaust valves and into the motor. And that can cause the motor to do something called hydraulicing.
When this happens, as you try to start the motor, the piston will try to rise but it'll have a lot of water on top of it. Because water won't compress, this usually either bends the conrod or breaks the piston. So when the water is above the exhaust manifold, you've got to keep the motor running at all times.
You should never allow the water to get above the air intake height – if it does, it will run in through the air intake, into the motor and do exactly the same thing as mentioned above. It’s important to have a snorkel fitted to your car before performing a water crossing as this effectively raises the height of the air intake to the top of the vehicle’s windscreen.
Assess the conditions
You can stand on the bank of many rivers and by looking across, work out everything you need to know: how deep it is (roughly), how fast it's flowing, what the base is composed of and what the approaches and exits are like.
“If it's a fairly shallow approach and a shallow exit, it'll be fine for you to drive through. But if you look across to the other side and you see it's a steep exit and there are deep ruts with mud splashed everywhere, you can probably assume you're going to have trouble getting out.
“If you've got a winch on the vehicle, get your gear out first and get it set up and ready to go in case you need to winch yourself out - you don't want to be hanging around in the water any longer than you have to,” says Kennedy.
The river bed
Check whether the river bed is sandy, pebbly, muddy or rocky so you can set the vehicle up for what’s in store.
“If you've got a river with a sandy base, you’ll need to let your tyre pressures down as if you're driving on a beach (12-15 psi on most cars). If you don't do that you could get bogged.
“If there are boulders and the like in the river, you want to be aware of where they are and avoid them. Sometimes, however, you won’t be able to see them – so you need to be ready to hit them – this will bounce the car around and feel quite uncomfortable, so be prepared.”
If you can see that the water is flowing really fast, you need to work out whether or not you'll be able to drive through it.
“The only way you're going to find that out is to go for a walk – you have to walk across the river. If you can take steps across the river without being washed over, your car will probably cope with it. But if you get pushed over every time you pick up your foot, your car will likely get washed away as well – so don't drive in, it's not going to work.
“It isn’t a science, but in my experience that’s the best rule of thumb. If you can walk it, usually a vehicle will be able to drive it,” says Kennedy.
When you enter the water, drive in slowly and then build your speed up. If you hit the water too quickly you'll start to aquaplane.
“A lot of people charge at it – they hit the water, float and then they're off down the river. If you drive in gently and keep the car on the ground you'll have a much better chance of getting through.”
Always use low range in water crossings. You want to be in first or second gear depending on your vehicle, if it's a Range Rover or Land Rover you'd be in second gear, other cars – Navaras and some of the lighter twin cab utes for example – you should probably be in first. If it's an automatic, pull it into the gear you want to be in (don't just leave it in D for drive). That way you know it's not going to change up or down at a time that's inappropriate for you – you want to be able to keep it in that gear the whole time.
“Try to establish a pace that creates a bow wave. This is where you're pushing a wall of water in front of you – you're getting a build up of water in front but at the back of the car, the water's opening up.
“It's a little bit like being in a bathtub where you splosh the water and it goes to the end of the bathtub and comes back again. In a river, we don't have the end of the bathtub so it just pushes and it just keeps going in front of you and if you get that bow wave right, you'll actually follow it through the water so it sort of pulls the car through: you're going with the momentum of the water,” says Kennedy.
Using a water bra can make it easier to create a bow wave and mitigates the risk of damage to components such as plastic radiator cooling fans by reducing the pressure of water entering the engine bay.
Dry it off
When you get out the other side of the river, make sure the car is dry before turning it off. Just leave the motor running or go for a drive for 10-15 minutes to dry everything out. According to Kennedy, parking the vehicle wet (especially if you leave it overnight) can cause parts like the breaks and clutch to rust and seize up.
In case you don’t make it
When you're driving through the river, always have a downstream-facing window open, so that if the car fails and you have to get out, you can climb out through the window and get up on the roof.
“People often drown in rivers because they do the wrong thing. They jump into the water thinking they're going to swim from a to b – it might not be very far but if there’s a decent current they're going to get washed away. Stay in the car or on the roof until you work out what you're going to do to get people off there. Don't panic - that's the key.”
While there’s a lot to consider before attempting a water crossing, as long as you prepare your vehicle and make a thorough assessment of the conditions before crossing you shouldn’t have a problem.
“It's mainly about keeping sane and sensible about what you're doing. Drive at a sensible speed and don't go too fast,” says Kennedy.