Technology

The people who buy new vehicles usually do it for the warranty that lasts several years so the cost structure of ownership is entirely predictable.

You can also buy a 25 year old Volkswagen 1.9 tdi. Some years your cost of ownership will be fuel and oil changes (and those cars basically take no fuel), but at some point you'll need new unit injectors costing 2-3x the car's value for a set. Will it be the month after you buy the car, or will it be in 5 years? It's a lottery and you're better off replacing all 4 when it comes to that, rather than doing one at a time.

Cars in the range of 5-15 years of age are even worse because they're more complex and some of the parts are super expensive. And it takes around ~10-15 years to know if an engine or transmission design is truly reliable (if it has big problems, we might find out sooner).

I'm going to use German cars as an example again because those are the ones I know best, but for example when BMW had the M57 diesel, that was basically the best modern diesel engine. 500k km? 700k km? No problem whatsoever. Only real issues would be the occasional injectors, turbo and maybe some coolant hoses, but those usually started surfacing after 300k or 400k km, at which point you expect SOME issues.

Then N57 came out as its replacement and a few years later we knew about the potential chain and valvetrain issues. Kinda sucks, because they'd also moved the chain to the rear of the engine, but you can get it done for a few hundred euros yourself, or somewhere between 1500-3000€ at a shop. But it took nearly a decade before we knew about the crankshaft issues and those are an engine killer. I'm talking a full rebuild of the bottom end with a NEW, not re-ground crankshaft since these have a special coating from the factory IIRC. Prepare around 10000€, which incidentally could be more than the car is worth by the time you find yourself doing this work.

Now that engine's replacement, the B57, has been out for 8 or 9 years and as far as is currently known, it has nearly no typical issues beyond some plastic coolant pipes that get brittle over time. But we don't know what other common issues might start surfacing as more and more of those engines reach high mileages.

Now if what you're thinking is "just buy a Toyota and you'll have no trouble", well, Toyota has made absolutely horrible engines in the past, for example the 2.2 diesel. Head gasket failure was notoriously common. Again, something that you wouldn't necessarily know when you're buying a 5 year old car because the issues haven't started surfacing en masse yet.