Ok it's a trick question really.
Anyway, there was (a correlation) for me this OCI because it's rained every weekend for the last month so I kept putting off my overdue oil change. I finally got it done today and it ended up being about 17500 km over a 7 month interval. It's 2005 Prius running Castrol Edge 5W30 btw.
So does anyone else use bad weather as an excuse for extending the drain interval?
BTW. The old oil didn't look too bad. Though I have to admit that I'm not 100% sure what I'm supposed to be looking for. Mine's always black anyway, because I use MoS2, so color is no guide. I usually just check that it drains smooth and consistent, that the viscosity feels about right and that there's nothing chunky, sludgy or gritty looking in it.