0W-20 is only their for the sole purpose of CAFEMy 2009 Scion has the troublesome 2az-fe engine. A piston soak plus a couple of flushes have greatly Improved oil consumption from a quart in <300 miles to now >1000 using a CK-4/SN rated 5w-40 HDEO. I’m very pleased with the reduced consumption and am hopeful that using the HDEO will result in even more cleaning of the oil control rings and drain holes.
My question is about long-term use of a 5w-40 HDEO in an engine that’s supposed to us a 0w-20 PCMO. The engine has 154k and the car is a spare/beater, so the world won’t end if it dies, but obviously I would prefer that it not. What’s better for a car in the long term: using the oil grade it specifies or using one that helps significantly reduce consumption? My gut tells me they wouldn’t give an oil an S rating unless it was OK for extended use. Right?