Our Family owns two Skyactiv G engines in the form of recent models of the 1.5 Liter Mazda engines found in the 2019 and 2020 Toyota Yaris compacts (formerly Yaris iA/Mazda2). They take the Toyota 0W-20, which I schedule for 5000 mile or 6 month intervals. [ Toyota is more encouraging toward 10,000 mile intervals as well as lifetime automatic transmission fluid, neither of which thrills me. We are making an effort to keep these cars on toward 200k miles each.]
My problem is that I noticed RISING OIL LEVELS on the dipstick of my 2019 Yaris, and when my wife bought a 2020 model, it was there again. Oil creeping up on the stick. [Level garage, checked in the morning quite carefully and repeatedly]
So I sent in an oil sample from my most recent service checks - one car at 35,000 miles the new one at 13,000 miles. By the time of the oil change they were both up several mm over the original top mark on the stick.
The reports showed- FUEL IN OIL at 2.0% after a 4000 mile interval, and a 'flashpoint' lowered correspondingly. All other oil parameters were normal, and the oil looked good.
I'm going to repeat the samplings at my next oil changes, which will now be aimed at 3000 mile intervals, until I know how well this diluted oil is treating my engines.
These are direct injection, 13-1 compression ratio engines, but they have good reliability and longevity records, as traced back through Mazda cousins.
What to do? Suggestions welcome! I will consider changing to a 5W-30, if the fuel continues to show in the crankcase oil, to adjust for this fuel-thinning effect. My Toyota dealer might balk at that on the 2020 Yaris which is still under warranty, but I'd do it on my 2019 car, to try to lower engine wear over time.
BTW- These cars don't get revved out too often. My 2019 does mostly mellow country roads between 30 and 55 mph with occasional town driving, while my wife's car is almost all short trips in town- which is challenging for the oil I know.
Any perspectives or advice would be appreciated.