What you need to know about flood-hit cars

Modern cars handle various conditions, but if floodwater reached the door's base, don’t drive.

Flooding rains can reshape landscapes and ruin infrastructure but they also inflict water damage on vehicles.

Many of these will be written off and scrapped, but some owners might be able to keep their cars on the road and others will attempt to pass them on unethically.

Modern vehicles can cope with a surprisingly wide range of conditions but if floodwater has reached the lower levels of the doors before receding, don’t even try to drive it (just as you mustn't drive into floodwaters: not only will doing so ruin your car, but it could also cost you your life).

Water can ruin mechanical components – destroying combustion systems or spoiling lubrication in transmissions – and also electrical systems located in the passenger compartment including airbag computers, which are typically positioned under the front seats.

A saltwater event is more likely to cause fatal damage to a chassis due to its corrosive properties and is obviously unlikely inland, but freshwater flooding tends to clog cars with mud and silt which increases repair difficulty and cost.

It is vital to contact your insurer before commissioning servicing or repairs, as it may be deemed not viable from a financial point of view.

In the admittedly unlikely event the car is declared useable – and a wet car is more useful than no car at all, at least in the short term – then servicing will be required before use.

Key safety components such as steering and brakes will need to be tested, all fluids will likely need to be drained to combat contamination and all cooling and ventilation systems must be checked for debris.

Petrol engines typically need to be hand-turned with the spark plugs removed to drain fluid from the cylinder chambers but diesel blocks require more complex solutions.

Transmissions must be checked and overhauled if necessary before attempting to start the engine, while wheel bearings also need to be attended to if affected by moisture.

Water-affected electrical components can start working again when dried out (usually after dismantling and cleaning) but there is a long term risk of corrosion-related reliability issues.

As you can see, even a vehicle that can be made driveable after flooding is not a good long-term ownership proposition – but this won’t stop some from trying to pass waterlogged cars onto unsuspecting prospective buyers.

Most flood-damaged vehicles will be written off and would typically only re-enter the market illegally as part of rebirthing schemes, which is why it is always essential to carry out registration and history checks before purchase, but those that are legitimately registered can be picked out by the following indicators:

Mud or silt under seats or dash, or inside glovebox, ashtray, ducting or filters;
Rust in the spare wheel, tool pouch or boot wells;
Damaged or missing logbooks and service records;
Corrosion of unpainted metal components, both inside and out;
White, powdery corrosion on alloys and green, powdery corrosion on electricals.
General interior wetness or dampness is an obvious sign but like all of the above, in isolation it could have an innocent explanation.