How to spot a flood-damaged car

Both countries flood, and both have flooded badly and repeatedly over the last few years. Every event writes off cars by the thousand. A proportion of those get dried out, cleaned up and sold on, and while plenty of that is done honestly and disclosed, some of it is done four states or one Tasman away from where the water was.

A flood car is different from other damaged cars because of the delay. Crash repair is finished when it is finished, and you can look at it. Water gets into looms, connectors, seatbelt retractors and control modules and corrodes them from the inside over a couple of years, so the car sails through your test drive and starts playing up long after you have stopped thinking about how you bought it. Nothing undoes it. A very good clean just hides it for a while.

1. Check the records before you drive anywhere

A car written off by an insurer for water damage is normally recorded as such, and that record stays with the vehicle. In Australia that is the written-off vehicle register your state keeps. In New Zealand a vehicle imported after damage carries it on its record too, which matters here far more than people expect, given how much of the fleet arrived as a used import.

It is the cheapest check there is, and it is the one everybody skips because the photos look fine. Do it before you commit a Saturday.

2. Use your nose first

Get in, shut the doors, and just sit in it for a minute before you look at a single thing. Damp, mould, and the smell of something trying to cover both. A brand new air freshener in a private sale is worth clocking. Then put the fan on full with the air conditioning off and smell what comes out of the vents, because a wet heater box will tell you within about five seconds.

3. Lift the carpet. Do not just look at it

Carpet dries. The underlay beneath it, a thick foam pad glued to the floor, holds water for months, and replacing it properly means pulling the seats and the centre console out. Almost nobody does that on a car they intend to sell.

• Peel back a corner in the front footwell and again in the boot, and press the underlay with your fingers. You are feeling for cold and heavy rather than obviously wet.
• Look at the metal under it. A flat, level line of surface rust running across the floor pan is not something ordinary wear produces.
• Check the spare wheel well. It is the lowest point in most cars and the last place anybody vacuums, so silt, a tide line, or a rusty jack in an otherwise tidy car tells you plenty.

4. Look where the silt settles and nobody cleans

Flood water leaves a fine grit behind, and it ends up in the places a detailer physically cannot reach. Take a torch. You will look daft on your knees in someone's driveway and it is still the best ten minutes you will spend.

• Seat rails, and the bare bolt heads holding the seats down. Unpainted steel goes first and never gets replaced.
• The seatbelts. Pull each one right out to its stop and look at the section that normally lives inside the pillar. Staining or a tide mark down there is one of the hardest things to fake.
• Up under the dash behind the pedals, and the back wall of the glovebox.
• The bottom few centimetres inside the door cards, and the drain holes along the lower edge of each door.
• Under the bonnet, in the seams around the strut towers and in the battery tray.

5. Assume the electrics are the real damage

Water and grit sit in multi-pin connectors and corrode the pins from the inside out. What you get eighteen months later is a fault that comes and goes, which is the worst kind to own, because there is nothing to find on the morning it is booked into the workshop and you pay diagnostic time regardless.

So on the test drive, work every electrical thing in the car, one at a time, and take your time doing it. Every window from both switches, central locking on each door, mirrors, all the seat adjustment, rear demister, wipers on each speed including intermittent, every exterior light, the stereo through each speaker, the reversing camera, the horn. These cars almost never fail on something dramatic. They fail on one window that hesitates.

6. Notice what is suspiciously new

A twelve-year-old car with brand new carpet is telling you something. So is a fresh headlining, a replaced set of seats, seatbelts that look newer than the car, or a new stereo in a car with nothing else upgraded. Each one has a perfectly innocent explanation on its own, which is exactly why you are counting them rather than reacting to any single one.

Headlights are worth a second look too. Condensation happens to plenty of cars and means nothing much. A flat horizontal line left inside the lens by standing water means something else.

7. A flooded hybrid or EV is a walk-away

This is the one item here with no inspection step attached to it. A high-voltage pack that has been submerged is not something to assess in a driveway with a torch, and the failure mode is not an inconvenience. If a hybrid or an electric car shows the signs above, leave it, and do not go poking about to satisfy your curiosity.

What a clean result actually buys you

One catastrophe ruled out. It tells you nothing whatsoever about what the model does in the ordinary course of things, which is what most used cars actually cost their owners over five years. A Corolla, a Mazda Demio and a Nissan X-Trail can all pass this list on the same afternoon and still have completely different weak points waiting at completely different mileages.

So do both. Ten minutes on the records, ten minutes on your knees, and ten minutes reading what the model is known for.