So you’ve found the holy grail of used cars: it’s an older model so it’s cheaper than a newer one, and it has really low mileage. The perfect score, right?

It could be, but that’s not always the case. Before you buy it, you should know about the problems that can pop up when a car isn’t driven very much. That bargain could ultimately end up costing you more than one with high miles.

Anything with moving parts will eventually wear out and need repairs, if it can be fixed at all. (I’m always leery when someone brags about owning a vehicle with ridiculously high mileage. Some are legit, of course, but your car doesn’t really have 600,000 km on it if you replaced the engine at 300,000.)

So it would seem logical that a car with 90,000 km is that much closer to its final resting place than one with 60,000 km. But where and how the car racked up that mileage can be more important than just the numbers themselves.

The average consumer vehicle travels about 20,000 km per year. We’re not warning you away from an eight-year-old car with 125,000 km on it, which would be a reasonable variant. But if it’s well under half that, then you need to be cautious.

Maintenance schedules include recommendations for more frequent oil changes if the vehicle is subject to “severe driving conditions.” Many people think this means the brutal stuff, such as pulling a heavy trailer, or in extremely hot or cold ambient temperatures.

Those certainly count, but severe conditions also include a lot of stop-and-go traffic, or a lot of short trips. It’s hard on your vehicle to start it and drive only a short period, such as ten minutes or less, because the engine doesn’t reach its ideal operating temperature. Combustion produces moisture, which disperses when the engine is hot enough. If it doesn’t, that water can dilute the oil and cause rust inside the engine. Moisture also remains in the exhaust system, which can damage the catalytic converter.

Thinking that “severe use” didn’t apply to him, that car’s owner might not have changed the oil more frequently—and might have even left it longer than normal, since many people go by the mileage, not by the time intervals.

Less-frequent maintenance may also mean that the cooling system hasn’t been flushed regularly, so the coolant has broken down and isn’t protecting the radiator and water jackets from corrosion.

There are other possible issues. Rubber seals can dry out and become brittle, as can hoses and lines. Tires that sit for long periods can develop flat spots, and gas can get gummy and clog the fuel injectors.

The first thing is to find out the car’s history. Ask the seller for the maintenance records, and check the intervals and mileage. If the car went for long periods of time between oil changes while racking up very few kilometres, you may be looking at a potential problem.

Ask where and how it was driven. A car that was used less frequently but was taken on long trips each time will likely be less of a headache than one driven daily for a short distance. If the seller mentions “highway miles,” ask about that, too. There’s a big difference between a wide-open freeway, and commuting on the highway in rush hour. That usually involves accelerating hard, jamming on the brakes, and then getting back up to speed, over and over. That’s hard on everything, and you could be the owner who winds up paying the price.

If you buy the car, change the oil and flush the cooling system before you start piling on more miles than it’s seen in the past. Replace any hoses that are brittle or really soft, and make sure there aren’t any cracks in the engine belt. Check the fluid levels frequently until you’re sure that nothing’s leaking.

Should the vehicle have really low mileage, treat it like a brand-new one, and follow a break-in period. Drive smoothly, avoid racing the engine or braking excessively hard, and if you’re planning on using it for towing, let it get about 1,000 km or so under its belt first before you hook up your trailer.

So what happens if you find the opposite—a vehicle with very high mileage? It could be a deal if it’s cheap enough, but do the same homework listed above. Don’t assume that oil changes were done at regular intervals, especially if it was a fleet or company car. If they don’t own the vehicle, busy executives may not always take the time to get maintenance done. And if it was a rental car, who knows how it was driven and how many curbs it hit?

Make sure you know if the engine uses a timing chain or timing belt. If it’s a belt, look up the recommended replacement mileage: the owner may be selling the car because it’s coming due. It’s expensive to change, and even more so if it breaks. If the seller tells you it’s new, don’t just take his word for it, but ask to see the paperwork.

A used car is always a bit of a gamble, but if you’re looking at mileage extremes, you need to dig deeper. Find out why it’s out of the normal range and what’s been done to it. Never go on price or the odometer without checking. That’s a wager you can easily lose.