Step One: Know your weapon
While flood water will eventually seep into electronics, transmissions, oil sumps, and car interiors, this takes time to happen. During flood crossings, the real danger is water entering the engine. To an engine, inhaling a slug of water is much like swallowing a shot of cyanide. It's instantly fatal.
Water is nearly incompressible, and an engine trying to squeeze it inside a closed cylinder will stop dead. This is called hydrolock. Valves, rods, pistons, and even engine blocks will break long before the water even starts to give. Preventing hydrolock means keeping your air intake dry. But most of the cars these days, even some so-called “SUVs,” have air intakes positioned much, much lower and more vulnerable to water ingestion, so here are some tidbits that you need to know about your weapon.
- Common amongst modern sedans and crossovers, the air intake tube is situated behind the bumper or headlight. It is shielded from water splashing over the front of the car, but not from water inside the engine bay. And it takes mere seconds for water to pool up inside the engine bay during a flood crossing.
- In some trucks, the intake sits under the hood above the grill with a splash shield under it. However, bow waves that go over the hood and stopping are still a danger, so it is still best to proceed with caution.
- But more often, tall SUVs and pick-ups have the tube pointed into the fender and have a separate air pocket from the engine bay. In this situation, the fender diverts water from the pocket behind it. This set-up often has large filter cans, so that water sucked into the tube will take much longer to reach the engine.
- One option that off-road enthusiasts love to have is to add a snorkel. It's an intake extension that exits at roof level. Theoretically, this allows vehicles to cross flood water that comes up to the windshield. Unfortunately, that’s only theoretical. Many modern cars these days have electronics located in the engine bay that will malfunction if submerged under water. And even if you do have waterproof electronics, your vehicle will start to float and can get carried along with the current if the water gets too high. In fact, even just 9 inches of water can sweep your car away.
Step Two: Know your enemy
When faced with a flooded roadway, ask yourself the following questions: (1) How deep is the water? (2) Where are the gutters and open manholes? (3) How far it is to dry ground? (4) Is the current is strong enough to carry you over the edge of the road? and (5) Where are the edges of the road?
If you can’t answer even one of these questions, then why risk it? Choose your battles wisely. Whenever possible, find an alternate route, preferably one leading to higher ground or the nearest multi-storey car-park.
Step Three: When all else fails...
While off-roaders tackle river crossings for fun, driving into uncontrolled flood conditions is like jumping off a foreign cliff to practice rock climbing. But since you’re already here, buckle up and read on.
- Have a plan of attack and an escape route. If possible, walk it out to scope how deep it is. Find possible escape routes, U-Turns, and higher ground should the crossing prove too treacherous.
- Don’t be fooled by low water at the flood’s edge. It can get much deeper past the point of no return.
- It takes less than a foot of water to carry a car away. If there is a moderate current and the water reaches the bottom of the car, stop right there. Mission abort.
- Hot metal and water don’t mix. If your car has been running hot, let it cool before attempting a crossing. Quenching hot components in cold flood water can cause metal to contract, leading to leaking gaskets.
- Deflate your tires... just a little. While higher pressures (35 to 40 psi) help prevent hydroplaning on the highway, slightly lower pressures (25 psi) help prevent a puncture should you hit a rock or an open manhole.
- Keep your windows open, especially if they’re electric. When the car breaks down, better to climb out a window than to open the door and let water in.
- Maintain a steady, slow speed while crossing. Keep the vehicle in 1st gear (or L for automatics). A speed of around 8 to 10 km/h builds up a gentle bow wave that will push water away from your engine bay. Going faster may cause water to splash and surge over your hood and into your engine bay.
- Do not change speed or gears while crossing. Do not accelerate, stop, change gears, slip the clutch or do anything that will cause water to slosh into the engine bay or seep into the transmission.
- Avoid crossing against oncoming traffic or beside trucks. Bow waves from large vehicles can push flood water up into your air intake. On the contrary, driving behind the wake of a truck can help you ford deeper areas than you normally could. Of course, if the truck should slow down or stop for any reason, you’re toast.
- Stay close to the center of the road, as it's usually higher, and there’s less chance of hitting an open gutter or canal.
- If the vehicle dies, DO NOT RESTART it. Climb out, push it to safety (if possible), and wait for it to dry out. Restarting a hydrolocked engine may cause irreversible damage.
- After crossing, check your car. Check all fluids for water contamination, and make sure that your radiator fans are turning freely. Dry your brakes by pressing on the brake pedal lightly while driving. It is advisable to bring your vehicle to a service center to have it checked the day after you cross a flood.
In the end, you will have to decide whether getting home a few hours earlier is worth the risk of damaging your car. For those of us who don’t have money to burn, the answer is obvious. Spending the night shacked up at the nearest 7-11 is always preferable to spending it muddy, wet, and cold in the back of your car while waiting for a tow truck.
Trust me, I’ve been there and done that, and it’s just no fun at all.