I have heard that oil level should be checked regularly on fill-ups (every second fill-up or so). However, on my car (a 2016 Toyota RAV4 hybrid), the oil level was full when I bought the car as new. It is still after 9000 km full, i.e. there doesn't seem to be any visible oil consumption. I drive about 15000 km per year, and the service interval is year or 15000km whichever is less. The situation seems to be even better than in my 2011 Toyota Yaris which consumed oil, but the 1.5 liter difference between high and low marks meant I never actually had to add any oil.
How often should I check the oil level in these circumstances? As far as I know, the engine doesn't have an oil level sensor (but it does have an oil pressure sensor). I think the Toyota engineers thought that if they design an engine that doesn't consume any visible amounts of oil, they can avoid the cost of an oil level sensor. So, on one hand, it's up to me to check the oil level. On the other hand, the oil level just doesn't seem to go down.
Is it safe to check the oil level twice per year every time I change the tyres (have to use winter tyres at these latitudes)? That means the longest interval between oil level checks would be 7500 km / half a year. This doesn't mean that if the engine starts to consume visible amounts of oil that I would still continue to use this same interval; I will in this case make the checks more frequent.
Is it possible that due to some event the engine would start to suddenly consume oil? Or can I rely on the theory that if the engine seems to consistently have a zero oil consumption, that it will continue to have a zero oil consumption in the future? Of course, if the engine needs any overhaul (unlikely), I will start to monitor the oil consumption situation regularly after the overhaul.