Driving to beat floods

It is ironic that in our country where there's often a shortage of water, we also sometimes come across flooded roads, overflowing storm water drains and rivers bursting their banks, as happened in Gauteng a few weeks ago.

What should a motorist do (and not do) in such conditions to ensure the safety of their vehicle and passengers?

l Avoid driving through water when you are not sure how deep it is. Stop the car before entering a flooded section and check the water level ahead.

Generally, if the water is deeper than the bottom edge of your doors or the bottom third of the wheels, it is not advisable to attempt to drive through it. If possible, seek a detour rather than braving the flood and risking costly damage to your car's electronic control systems.

Depending on where the air inlet to the engine is situated, you also run the risk of water being sucked into the combustion chambers.

Water cannot be compressed, so when a fast-moving piston comes up against water trapped inside the combustion chamber, it is like hitting a wall (the technical term is hydrolocking).

This has been known to bend a conrod or crack a cylinder head. Even if the water doesn't get through to the combustion chambers, it might get into the air filter and a wet air filter will restrict the flow of air into the engine. On a diesel engine this will lead to excessive combustion temperatures which can seriously damage pistons.

l If you have no other option but to drive through flood water, proceed slowly and steadily to avoid creating a bow wave.

On a manual transmission car, engage first gear and keep the engine running moderately fast while slipping the clutch just enough to maintain momentum.

This keeps the exhaust gases moving, helping to prevent water from entering the tailpipe. With an automatic transmission, you should likewise keep the car in first gear and keep the revs up while feathering the brake to keep the speed down.

Driving like this is not healthy for a clutch or automatic transmission, and it should not be done for longer than necessary.

l At night it's much more difficult to see water hazards, especially if it is still raining heavily. It can be hard to distinguish between a wet road surface and stagnant water, for instance. It helps to keep an eye on the fences, plants and walls at the side of the road - if these appear unnaturally low, slow down at once because the road is probably flooded.

l Prepare yourself mentally to handle a skid. Losing control of a car on a wet road is a frightening experience. It happens in the blink of an eye, and you have to react very fast to "catch" it. Ease your foot off the accelerator and steer in the direction you want the front of the car to go.

This procedure, called "steering into the skid", will bring the rear of the car in line with the front. Avoid braking on cars without ABS. On ABS-equipped cars, brake firmly as you steer into the skid. Remember also to test your brakes gently immediately after negotiating deep water. They might need time to dry out before you can trust them.

l After driving through flood water, there are a few things to be done when you arrive at your destination, even if your vehicle seems fine.

Inspect the engine and transmission oil. If it looks milky, beige or diluted, water has got in and the oil should be drained as soon as possible. Check the air filter - if it is damp, replace it immediately. Look underneath the car for stuck-on debris or mud which should be washed off.

Check the lights and indicators for water inside them, especially on older vehicles with degraded seals. If water is noticed, the units will have to be partially dismantled to dry them. Replace the seals at the same time, perhaps with silicone beads.

n We would like to invite you to write to our expert columnist about any motoring issues. This is your page, please send your questions to guru@sowetan.co.za. Deadline for all the questions is Friday midday. Many thanks. - Mabuyane Kekana