Driving through deep water

Check your maximum wading depth

Wading depth is set by the manufacturer of your vehicle and is determined by a number of crucial factors. These include the location of sensitive electronics, the air intake, and other venerable areas. Often the manufacturer will assume you'll only be wading for a few minutes, so if you intend on regularly crossing rivers some additional preparation may be required. Consult an expert if you're considering a serious expedition. It's a good idea to have a reference point on the vehicle as an indication of the wading depth - usually the top of the wheel rim is a safe bet, but consult your handbook for more information.

Accessories

The following accessories may be required for sustained wading in deep water:

• Wading plugs or tubes for the gearbox and differentials to prevent water ingress
• Sealed air intake snorkel to prevent water entering the engine
• Radiator barrier to lower the water level in the engine bay
• Splash baffles can prevent the fan throwing water everywhere in your engine bay

Preparation

• Disconnect or disable fans if necessary to prevent damage to the fan blades and reduce the amount of water thrown around inside the engine compartment.
• Ensure you have no fluid leaks which could be potentially hazardous for the aquatic wildlife.
• Pre-attach a tow rope to your recovery points if you think there is any risk of getting stuck - attach on the side of the vehicle you're most likely to be recovered from.
• Perform a recce to determine the best route.

Recce

If you are in doubt about your ability to cross, get out and walk the route (fishing waders come in handy here). Check the ability of the ground to provide traction and support and look around for hidden obstacles. Use a marshall if necessary to provide a visual indication of any hazardous areas. If you intend on crossing flowing water, check the speed of the flow - remember that a car will float and can get carried away downstream pretty easily so don't attempt this unless you are very experienced.

If in doubt, abort the crossing and find another way round!

Technique

Whether you're entering a river, lake or a deep trough, you'll find most areas of water have a steep entry (a) and exit point (c) and submerged ground under the water which may or may not provide decent traction and support (b).

Diagram 2: The anatomy of a deep water trough

Entering the water

When you descend the slope it's sensible to use exactly the same technique described on our hill descent article. Enter the water gently in a low gear to prevent a huge splash. Then accelerate slightly and change up if necessary when you're on the flat.

Diagram 3: Entering the water

On the flat

Select a gear which provides a decent amount of traction, but reduces the chance of engine stall, and keep the engine in the power bend. Second gear in low range (if fitted) is usually about right, but if you don't have low range it's probably best to stick to first.

By driving slowly and steadily (jogging pace) through the water you'll find that a bow wave naturally forms in front of the car. This is useful as it artificially lowers the level of the water at the front of the vehicle, crucially around the engine bay and air intake.

Diagram 3: The bow wave

Follow the wave and try to keep it about a metre in front of your vehicle for the best results. This provides an additional layer of protection for sensitive vehicle components, however if you stop this effect is cancelled out. Make sure you can keep going once you've entered the water by doing a recce or following the path of a successful vehicle.

Don’t let the engine stall – gas pressure will prevent water entering the exhaust pipe while the engine is running even if it's completely submerged. But if you turn the engine off or stall the rapidly cooling gas will suck water up towards the engine and can clog up and damage the catalytic converter. If you do stall, try to restart the engine as quickly as possible and you should be ok, but if it won't start wait to be recovered to prevent costly engine repairs.

Exiting the water

When you're getting close to the other side it's a good idea to ease off the gas - as the bow wave hits the bank it will come back towards the car and can splash well over the bonnet if speed isn't reduced. Climb out of the water using the techniques outlines in our article on climbing hills and you've made it! Reconnect the fan if necessary and continue on your adventure.