Bear in mind that every car over a certain age has to have an MOT once a year yet many people running older cars often skip on servicing, preferring to rely on a wing and a prayer instead. I believe regular servicing will have a much greater effect on the longevity of an engine, irrespective of size?

Yeah I agree regular servicing will have a greater effect and equally the actual quality of the engine probably has an effect. If it was true that larger engines were more reliable though I was hoping to see something in the overall data that supported this!

Correlation, but close to zero causation, I would guess.

Causation, I guess would go:

- Cheaper cars have smaller engines of lower quality

- Really expensive cars have larger engines, but in many cases those engines are optimized for acceleration, not longevity. Also, those cars may get crashed more often

Yeah there are so many hidden patterns and causes. It is almost impossible to say for sure what causes it!

Commuter cars get run to death then disposed of. Even if you just trade them in after a few years, the next owner is going to continue running them into the ground. It's why the ownership curve is inverse to the lifespan.

Cars with big engines are typically someone's second (or third or fifth) car, they get kept around longer because they're special, and also don't get driven enough to rack up kilometers.

The peak of longevity in sub liter cars is from most of them being classic micro cars and the rest being Japanese Kei cars. They don't get driven very far, but a large portion of them are from the 50's and 60's so they're skewing the longevity numbers and the mileage numbers.