Bridging troubled waters to ensure safe driving
By George Foessel
MORE people come to grief in water crossings than any other four-wheel drive situation. But the risk can be minimized by taking a number of steps to safely negotiate such hazards.
The first thing a four-wheel drive vehicle owner must know when negotiating a water crossing is the location of the air intake.
If in doubt, refer to the owner's manual or vehicle serving agent.
Once the height of the air intake has been established, assess the depth of the water you intend to drive across.
An engine needs air to run, therefore if you drive to a depth greater than the air intake, problems may occur.
Most new vehicle warranties only cover the vehicle up to a depth of about 500mm or hub height.
Water crossings should be approached in the following order:
* Ensure all recovery equipment is readily available.
* Walk the crossing to establish the level of preparation required. If the driver cannot swim, the crossing should be walked by a passenger who can. By walking the crossing the driver will establish the following:
1. The depth of the water.
2. Angles of approach and departure entering and exiting the crossing.
3. What the base of the crossing consists of e.g. sand, mud, rocks, etc.
4. What hazards or obstacles are hidden under the water, such as large boulders or fallen trees. Mark hazards with long sticks so you will not drive over them, damaging the vehicle.
5. How strong the current is. If the water is flowing so fast that you have difficulty walking the crossing, don't drive it. Otherwise, drive the vehicle slightly upstream so water is being deflected and not pushing against the flat side of the vehicle.
6. Mark the exit of the crossing with long sticks if necessary.
Once you have walked the crossing, you are in a position to determine what level of preparation you need to undertake.
* Park the vehicle and let the engine and drive train components cool down. The best time for this is while assessing the crossing.
* Cool diffs and gear box. Never drive a vehicle straight into a water crossing. This will stop water entering the differentials and gearbox, avoiding expensive repairs.
* Turn off the air-conditioner. If you leave your air-conditioner on during a water crossing, it can damage the condenser or break blades off the thermatic fan.
* Tarpaulin the vehicle if necessary. The tarp is fitted to the front of the vehicle with elasticized straps. This will stop water entering into the engine bay and avoid damage to the fan or radiator.
Special preparations must be made if the crossing is deeper than 500mm (knee deep)
If you have a petrol engine, spray the ignition components with dewatering fluid.
If you have a diesel engine, it is important to fit the vehicle with a snorkel (raised air intake). The result of water in a diesel engine is very costly.
A diesel engine should still be tarped on long deep crossings, even if it has a snorkel fitted, to avoid damage to the radiator and engine fan.
In deep water (above 750mm) it may be necessary to remove the fan belt. This will stop the blades hitting the water and breaking off.
Once you have completed the assessment, decide what speed and gear to use. Second gear, low range is usually ideal.
Enter slowly until the front of the car is in the water and immediately accelerate to a speed which will cause the vehicle to make a bow wave.
This is where the vehicle is actually pushing the water out of the way, not just wading through.
Do not drive into the water at speed because this can push the radiator onto the engine fan.
When assessing the crossing, take into account that empty or near empty long-range fuel tanks may cause the vehicle to float.
If this happens, your only option is to open the door down stream and allow the cabin to fill with water.
This will effectively sink the vehicle but give you traction. Check the brakes after exiting the water, they may not work.
To restore them, drive along slowly in first gear, pumping the brake pedal. This will build up heat in the braking system and dissipate any water.