Why is my high-mileage car worth less?

May 12, ‘Odometer Day’, has once again come and gone – without any discussion whatsoever of the role this device plays in setting used-car prices.

Not since Schroedinger’s box – the one he stuffed the cat in – has any device been so thoroughly mystifying.

It all seems perfectly simple: the odometer runs off the same system as the speedometer, but records distance rather than speed, which is distance over time, of course. But used-car buyers have become too reliant on the odometer to tell them the life story of a car. Over decades, the odometer has become an entrenched part of that car-buying culture.

That was fine when the odometer reading was actual testament that a vehicle had led a hard life.

Back in the 1950s and earlier, cars were just not that robust, mechanically. Few cars made it to 100,000 miles (160,000km) without some major work done on the engine or transmission. An odometer reading up around 100,000 miles was a sure sign that costly repairs were imminent.

But in the 21st century, there are plenty of vehicles that will travel great distances provided they’ve been properly serviced at the appropriate intervals. Even a high-kilometre car may conservatively have 100,000km of life left in it.

Don’t just look at the odometer, look at the car’s background. If it’s a long-wheelbase German limousine that’s been chauffeur driven most of its life, it’s probably in the first bloom of its youth – even with an odometer reading above 200,000km.

In contrast, perhaps you should exercise some caution if you’re in the market for a turbocharged, all-wheel drive small car that’s travelled less but is owned by someone who seems like he or she is on intimate terms with words and phrases like ‘blow-off valve’ and ‘wastegate’. Is it a car that may have travelled less than 10,000km a year – most of them to and from the illegal street drags on an industrial estate?

Even then, don’t be too quick presuming to judge the owner of that car from the stereotypes.

Sometimes, lower kilometres can indicate that the odometer has been ‘whizzed’ – a practice that these days involves plugging a cheap device sourced from overseas into the car’s OBD (onboard diagnostics) port to roll back the odometer -- sometimes by hundreds of thousands of kilometres.

The device practically pays for itself if there’s a difference of thousands of dollars in resale value between, say a car that’s on the cusp of turning over 200,000km and one that’s showing less than 100,000km.

Rolling back the odometer is illegal and hopefully has been all but wiped out. A licenced motor car trader can lose his or her licence if found guilty of rolling back odometers to sell cars at a higher price to unsuspecting consumers.

Perhaps the lower kilometres shown on the odometer are an indicator that the car has spent its entire life in bumper-to-bumper traffic. Worse still, perhaps it’s a second family car that is only run for short hops around the suburbs – never reaching operating temperature.

Maybe the car is 10,000 or 15,000km lower than average because it has sat in a panel beater’s workshop for several months after a bad prang while waiting for parts.

Whatever the case, look at the whole car, when you’re buying, not just the odometer. Keep an eye out for obvious signs of high-kilometre wear and tear (faded paint, for example, or worn carpet/floor mat under the pedals). This could be in conflict with what the odometer is telling you.

Better still, check the logbook for servicing. Any discrepancies between the services and the actual odometer reading will highlight something dodgy going on.

But what if there’s no logbook? A CarFacts report could help you determine whether the car is as advertised and the kilometres travelled over the course of its life are legitimate.

If you live in one regional town and work in another, half an hour’s drive away by open road, you’ll be adding roughly a hundred kilometres per working day to the odometer’s tally. Over a year that accounts for around 25,000km travelled, just commuting between work and home.

Even without additional trips to shops, or away on holidays or visiting friends and family, your car may be right on the cusp of clicking over to six figures with a year to go on the (five-year) factory warranty. This amounts to roughly double the average distance travelled by privately-owned motor vehicles in any given year.

No. As long as the car has been maintained in accordance with scheduled servicing, it has plenty more years of life left in it.

In the example of the country resident who travels to work half an hour away on an open road, the car is running at a steady speed, in top gear, with the engine operating at conservative revs and under light load, having reached operating temperature within five minutes of the half-hour drive commencing.

That sort of touring scenario just doesn’t get any easier for a car.

Contrast that with a car that only ever drives to the shops or drops the kids off at school. This car will barely reach operating temperature before the engine is switched off again (particularly problematic if it’s a diesel!). It probably won’t reach top gear and the engine will be under load, while cold, accelerating up to speed – and perhaps through a succession of corners.

And it’s not just the powertrain under pressure in short trips from cold starts. The brakes will get more use as well, and ditto for suspension and steering components...

The urban commuter car just has to work harder. It’s as simple as that.