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What Happens if Your Car Floods?

In days gone by, ‘flooding’ your car typically referred to getting the starting procedure wrong, but with the advent of modern fuel-injection systems, it usually signifies something that’s much worse—and potentially catastrophic.

To clarify, we’re talking about water ingress, either in the engine, or the cabin. Find out what happens to your car if it floods, if flooding is covered by car insurance and what to do if your car is flooded to prevent further damage.

Flooding your car

It seems that the term ‘flood’ is being used increasingly in this modern age; often we hear on the news that an area is flooded, houses are ruined, and the only way to reach safety is through the use of a boat. It’s this repeated association with destruction that’s at the forefront of our thoughts when confronted with water blocking our path.

And rightly so. Deep water still holds a mystery for mankind; four times as many people have walked on the Moon as have seen the deepest part of the Mariana Trench.

While there may seem little connection between the ‘Challenger Deep’ of the Mariana Trench (at 10,994 metres in depth) and driving through something more than a muddy puddle, the link is the force that can be exerted through water.

Internal combustion

A car relies on a number of complex systems and components to work at its best, from electronic control units through to high-tension ignition systems and careful metering, monitoring and adjustment of critical components.

To do this, a typical modern car uses in the region of 100 different electronic sensors, although as technology gets increasingly complex, that figure is set to double over the next few years. For many motorists, it’s the thought of getting the electrics & sensors wet or damaged that makes them hesitant when faced with crossing water. While there is an element of truth in that, the real danger comes from getting water inside the engine, a very real possibility, and the damage that it can cause.

All internal combustion engines (either unleaded or diesel) use the same basic processes: fuel is drawn into the motor, compressed, ignited and exhausted (suck, squeeze, bang, blow). Of course, both diesel fuel and unleaded petrol are stored in liquid form, but at point of combustion, they’re finely atomised and mixed with air; the typical ratio for unleaded fuel is 14.7 parts air to one part fuel.

Compressing the ‘charge’ is relatively simple as the main component is air. With that said, pressures inside the cylinder (where the ignition of the charge takes place) could be as high as 1,500psi at point of ignition, but when the air / fuel mixture is replaced with water, it’s the mechanical components that give way.

Given that water can’t be compressed, the internal pressure takes the path of least resistance; usually bending the connecting-rods between the crankshaft and piston, which in turn leads to further, significant damage of other components. The result is a repair bill that runs into many thousands, or possibly the whole vehicle being written off.

Inside the cabin

Flooding the engine with water can be an instant and catastrophic failure, but even if you’re ‘lucky’ and no water enters the engine, your car could still be significantly damaged by flooding. To be clear, we’re talking about water damage to the point of saturation, not just a light sprinkling.

Cloth trim will likely dry without too much issue, but leather trim will need significant work if it is to ever look the same again, and there will be a damp & musky smell pervading throughout the car which you may never get rid of. And let’s not forget where the water comes from, or the potential contaminants contained within.

Added to that is the loss or damage to electrical components; while many of the sensors, plugs and wiring harness extensions have a degree of water-resistance, the main components aren’t designed to be watertight. Replacing a 12” touchscreen infotainment system for example, could cost you anywhere £500 - £2,000+ once you’ve included the associated hardware and labour. And that’s just the start; modern cars use around 1,500 different wires, which equates to around one mile of copper.

At the end of some of those wires are ECUs (Electronic Control Units), and with technology rampant, the number of ECUs fitted increases with each new model, typically you could find around 150 ECUs fitted to a relatively luxurious, modern car.

Car insurance and flooding

If your car has been damaged in flood conditions, it may be possible to claim for the damage through your car insurance but, as you may expect, there are some caveats.

It’s highly unlikely that you’ll be covered by insurance with anything other than a fully comprehensive policy, and of course you’ll be subject to the individual terms & conditions of each insurer—not all insurers automatically cover flood damage. For those that do, it’s usually separated in two parts: Unavoidable and avoidable flood damage.

Avoidable flood damage would be considered as something like taking the decision to drive through a body of water deliberately; unavoidable flood damage could be as simple as having your car flooded while parked in its usual spot—at home for instance. Equally, if you’ve driven through water deep enough to stall your vehicle, trying to restart it could be considered reckless, and therefore may not be covered for any damage, either prior to or after trying to restart.

There are no hard and fast rules regarding flood damage; some insurers will cover it, some won’t. Most insurers that do offer cover may only cover mechanical damage, leaving you out of pocket (or looking at a potential claim on your home insurance) for personal belongings. And some will only cover flood damage through the unavoidable clause. Whether you're covered by a small or large motor insurance company, check the coverage when you take the policy out, or before you venture out among the storms.

Should you drive through a flood?

Off-road driving experts will tell you that you should never drive through water without first ascertaining the depth, what lies beneath, and any potential pitfalls or potholes. Of course if you’re the only vehicle to drive through such a flood, the implication is that you should first wade through the water on foot—although this can present it's own set of dangers.

If you’re in any doubt and there’s a viable alternative route, choose safety and peace of mind and don't risk flooding your car by driving through water.

That said, cars are water-resistant to a certain extent. While being careful not to advocate driving through deep water—that requires advanced knowledge—it’s worth understanding that even small cars are capable of wading to up to 12” in depth with no mechanical preparation. It’s generally accepted that 12” of water is enough to float some smaller cars, and as little as 24” could be enough to wash a car away.

It's also worth remembering that an experienced water forder might just make it through the same stretch of water and in the same vehicle, but with a different technique—and technique comes with experience. Generally speaking, it's safest not to take the risk of driving through flood water.

Steps to take if your car floods

If your car floods, there are steps you can take to mimimise the long-term damage. But first, whether you're cleaning up flood water from your home or your car, remember that flood water can be contaminated so wear protective clothes such as latex gloves and wellies, and wash up well afterwards.

  • If your car was in deep water don’t start the engine: There could be water trapped in the cylinders, which might cause damage if you try to start the car. Get your car towed to a mechanic instead.
  • Check the oil dipstick for water. If you see any water droplets on the dipstick, get the oil and oil filter changed before you drive your car. Also, the cylinders could be broken as they're meant to compress air not water.
  • Check the interior: If water levels were higher than the bottom of your car, it's very possible that water got inside the passenger compartment. Use a wet/dry vacuum to collect any remaining water in your vehicle, towels to soak up saturated seats and carpet and fans or dehumidifiers to speed up the drying process (this can help avoid mold and mildew from developing). It might be worth hiring a professional to remove all the moisture from your car.
  • Check electrical components: Your mechanic might need to replace electrical components damaged by a flood.
  • Check the fuel tank and line: See if there's water in the fuel by using a siphon pump to remove some fuel from the tank. If water is present, your mechanic will need to empty the fuel tank completely.

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