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by sjwright 2618 days ago
In theory the oils and engines have improved to the point where 10k miles is a sound number based on evidence. However given that the only downside to more frequent oil changes is the cost of the oil change, if you plan to keep a car for a very long time, changing it more frequently than the recommendation is a reasonable plan.

Longer oil change intervals are undoubtedly fine for an engine that is expected to last at least to the end of the warranty period. Which is all the manufacturer cares about.
1 comments
bluGill 2617 days ago
Actually long oil changes can be better for an engine. Oils break in: the molecules break down over time so they compensate by making the chains longer. As the molecules break down they get closer to the idea size, then the break again and get too short to protect.

Tests on the oils used in my car show that you typically get least engine wear between 8k and 9k miles, with 12k being about the same as fresh oil, but 13k is much worse. Because of the sudden dropoff at 13k and the fact that different driving styles affect breakdown differently 10k is chosen as the best compromise. Newer cars get longer because the computer keeps track of driving styles to give a better change indicator.

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sjwright 2617 days ago
That's genuinely fascinating and I'd like to learn more about it. Can you recommend some reading material for me? (Or better still an Engineering Explained-style YouTube video if someone has covered the topic well in that form.)
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bluGill 2616 days ago
The above was gained from reading forums. My personal judgement is the people saying the above know more about oil than me (they at least understand enough chemistry that my college chemistry doesn't see anything wrong, but I went into computer science so I didn't take more than the basic chemistry for engineers so it is possible that they are wrong on details.

One other point they brought up: every time you open the system to add or check oil dust gets in. Modern engines are generally sealed so this dust until it is filtered out (assuming it is) is doing wear as well. Long oil changes with no checking of the oil level are thus a good thing as well - so long as your oil level never gets low - low oil is far worse than any gain from not checking oil levels.

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