The only way to know is to consistently and regularly have used oil analysis done. For my part, I change my oil every 3k or sooner because my vehicle gets put on a race track occasionally, which changes wear patterns and an oil change is cheap insurance. For full synthetics on a car which mostly sees highway miles 10k intervals are fine, but 15k and 20k intervals are ridiculous. For most cars in the US which see significant traffic a 5k interval is correct as stop and go traffic is actually harder on the engine than almost anything else.
Side note: A kilometer is just a little over half a mile. A 10k KM OCI is equivalent roughly to a 6500 mile OCI. So there isn’t that much difference between the US and European intervals.
Maybe that was true decades ago, but it's no longer true. They prey on the misinformed. To be charitable, maybe they know many people wait too long, but I doubt it.
I went every 10k miles or so.
Other cars can go longer distances without an oil change, as you say.
In us oil changes are 3k-5k miles. which is ~5k km to ~8k km whereas in Europe it's 10k to 20k.
I find 8k-10k figure to be close enough and realistic.
5k km for old cars with non-synthetic oil.
20k km I highly suspect is a pipe dream from BMW marketing material ensuring that after about 120k the car would have no resale value.
Full synthetic oil/filter is about $60 to change here.
> Oil changes color as it captures contaminates such as soot, carbon deposits, etc. It can operate effectively while brown-ish, but if the oil is carrying too much it will blacken and start to thicken at which point it will be much less effective at lubricating your engine.
Modern synthetic oils last much longer.
Modern engines are designed with much, much better tolerances than before and crank cases no longer vent into the atmosphere. If you use new synthetic oil in an old small-block Chevy, the oil will hold up for a long time, but it will be so contaminated by gasoline, moisture, and debris that it will still require shorter replacement intervals.