[rerx]

I assume the costs of repairs and spare parts would also enter that equation.

[tomahunt]

An aside: it can be a good exercise to use the above reasoning to decide when to buy a new car

[marcosdumay]

That reasoning will push buying new cars away to the moment the old ones completely fail, and not a second before.

For cars it is much more important to calculate the risk of it failing in some moment you need it, and the costs of being suddenly carless. Also, for cars that go on a road, the most relevant factor is safety.

[willvarfar]

Having done the maths, and living in a country with very high fuel prices, I have to say that everything seems to be in favour of putting up with small old cars as long as possible!

[yardie]

It's also a good reason to update major appliances regularly. Washers that use too much water to fridges that are inadequate insulated.