Off-road series with Alan Pepper: how to drive in deep water

Off-road series with Alan Pepper: how to drive in deep water

Posted by Alan Pepper on 9 Jul 2018

Off-road series with Alan Pepper: how to drive in deep waterModern 4x4-ing is rife with debate. In this series, our expert tackles the best way to drive through water, and everything else you need to know about water and your 4x4!

Suzuki’s 4x4 expert, Alan Pepper, has spent 22 years tackling challenging roads with a variety of 4x4s. He bought his first off-road vehicle in 1975, and has been training thousands of people at Bass Lake for decades. Here are his thoughts on how people should be driving their 4x4. This is the start of our series on modern 4x4 driving. Have anything to add? Let us know on Facebook or Twitter.

Driving through water at speed, water cascading over the vehicle - oh what a wonderful experience! So exhilarating! Let’s do it again.

This is a scene that I have witnessed many times in my years of driving 4x4 vehicles, and if it’s mixed with mud so much the better.

However, deep water is without a doubt the quickest way to shorten a vehicle’s life. Suzuki advocates avoiding driving in water and mud as much as possible..  Always stick to the recommended wading depth as indicated in your owner's manual.

If water gets ingested into the cylinders while the engine is turning, and the piston tries to compress it, it will bend and break the conrod. This could cost you a new motor - usually at about 25% the cost of your vehicle. If the vehicle is fully submerged it can be totally written off! When water gets into the electrical systems, that can irrevocably damage the vehicle in terms of cost of repair... and remember water damage due to driver negligence is not covered by insurance or manufacturer’s warranty.

So how do we tackle water crossings?



Vehicles are water RESISTANT not waterproof. Waterproof is where you can fully submerge the vehicle, take it out of the water and it will be totally unharmed.

It’s true that vehicles are designed to be waterproof up to a certain depth. This will allow them to be driven in rain and withstand a certain amount of flooding - usually up to the centre of their axles. As axles and differentials have breathers on them they should not be submerged, and some manufacturers give specified wading depths on their vehicles. This means you can safely go to that depth without damage, at a speed where you create a smooth bow wave that does not break. If there is no specified wading depth do not go beyond centre of your wheel. If you do so it will be at your own risk!


The first thing that you will be “advised” to do is put a snorkel on your vehicle.

Snorkels are mainly used to get cool clean air into turbo charged motors to help keep the temperature down, so they run more efficiently. Look at all the big trucks on the highway - all of them have one. They run up the back of the cab, some point backwards and some run along the top of the cab facing sideward - but they NEVER point into the wind. The reason for this is that facing forward forces the air into the pipe and carries dust and rain into the air filter and can be forced into the engine, causing costly damage.  A word of advice when travelling in very dusty conditions: turn the top of your snorkel to face backwards. The problem is that they do not “look macho enough” but they are far better for your engine!

If you anticipate deep water crossings and don’t mind voiding your warranty by making aftermarket alterations, here is some advice from Alan,

STEP ONE: When starting to make your vehicle more waterproof, start from the bottom up. First lengthen your breathers on your diffs, gearbox and transfer case up as high as possible. Make sure to double them over so they face the ground that will stop dirt from falling down the tube.

STEP TWO: Next, make sure all your doors seal properly. Then the floor pan. A lot of vehicles have holes in the floor that are there from the factory. They have rubber plugs in them. Sometimes they are missing, and the water comes in through there, and that is why the carpets get wet.

STEP THREE: As we go higher up the vehicle the next thing is the fans. Some vehicles have solid driven fans, while newer vehicles have viscous fans that are heat controlled. Solid fans are a problem as they spray water all over the engine compartment and onto the electronics. The viscous fans usually run closer to the radiator and are made of plastic. If your viscous fan is running and you plunge into the water, the fan tries to act like a boat propeller. This bends the fan toward the radiator with disastrous results to both the fan and the radiator. When entering deeper water enter slowly, allowing your axles to cool down, and then proceed until the bottom of your radiator is in the water. As it cools the viscous fan will stop. Make sure your air conditioner is off because if the air con fan starts while it is in the water it will break the blades off the fan. As we progress higher up the vehicle we now encounter electronics... all those wires that very few people know what they do. Be aware - electronics and water do not mix! On modern vehicles control boxes cannot be repaired and must be replaced at a cost that could require you to take out a second bond on your home!

Now we get to the air intake which on most vehicles is housed in one of the fenders. Unless you go pretty deep and stop in the water, or go careening through the water, with water over the bonnet, you should have no problems. On fuel-injected vehicles there is an air flow sensor that absolutely can’t get wet. If it gets moisture on it at all, it will short out and stop the motor instantly, though it all depends on how fast the motor is revving when the water enters the air intake.

Just an aside… How much air does your motor use? Yes, it needs air (oxygen) to mix with the fuel to make it burn! Take a 2-litre engine. Being a four stroke, it inhales a fuel and oxygen mixture every second time it rotates. Therefore, it uses 1 litre of this mixture every time it rotates. That equals 1000 litres of air/ fuel mix at 1000 revs per MINUTE, which is slightly higher than an idle. Now take it to 3000 Rpm = 3000 litres lt/min. Imagine a vacuum cleaner sucking 3000 lt/min! That should give you an idea of how fast you can ingest water. Now you understand that there is no chance of water entering the exhaust with that much exhaust gas coming out.

Now we have prepared the vehicle for the water crossing, we approach the water.


How deep is the water?

This is answered by wading through the water before committing your vehicle to the water. Beware the sudden deep dips in the middle of the crossing!

What surface is under the water?

Mud, sand, rock or tar? Each has their own peculiar approaches.

Is the water fast flowing or stagnant?

Just a word of caution: when the depth of the water touches the sills of the vehicle it starts to have a lifting effect. You can expect 1kg of lift for every litre of water displaced, which means that the vehicle gets lighter the deeper it goes in the water, and the possibility of it being washed away increases.

A parting word of advice: Always prepare for a recovery! Have your straps connected to your vehicle before entering the water in case a quick recovery is needed. It’s also key to always have your windows open and seat belts off when driving through water, in case you fall into a hole or the vehicle turns on its side, which will let you escape easily.


Read more articles in our Off-road series with Alan Pepper:

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