It seems common that on car blog sites, very few people know some of the TRUE facts about the wonderful low-viscosity oils, which are more aptly called “water oils”, since they are about as thin as water.
Search for, or go to Castrol’s site, and read about it. You can dismiss what they say as sales talk, but it is not, and there are many mechanics, even Toyota Master Techs who agree that the use of 0W-20 oil is damaging to the engine.
The reason is that ‘water oil’ leaves almost no FILM on the cylinder walls, the rings, the bearings, and the overhead cam shaft. Castrol has found that it takes 20 minutes for a car to reach full operating temps and parameters, and that 75% of engine wear occurs when starting the engine after it has been sitting for hours. It doesn’t matter if it is winter or summer, particularly with water oils as they will just quickly leave parts without just about any lubrication.
It is also a known fact that Toyota has been making the same 2.5 L - DOHC 4 cyl engine design, called the AR, since 2008. From 2008 on, they all are basically identical with slight changes in hp. But they all are DOHC, 16V w/Dual VVT-i.
But, back in 2008 the recommended oil was 5W-20, when they began this foolishness solely to get more gas mileage to meet Federal CAFE higher mileage requirements. The other factor of making cars unsafe due to the absurd reduction in weight, effectively creating traveling tin cans of death, is whole other discussion that should be addressed in another post.
Toyota and other car mfrs. are making more MONEY by doing all this. They could care less about what is best for the engine; they simply want to cater to our Federal requirements, that are extremely misguided and myopic.
Many mechanics, even at Toyota, back in 2008-2010 or later, knew what nonsense water oils were, and they would use weights as high as 10W-30, and the engines operated just fine, and had a good film strength coating the engine parts. Even a 10W-30 synthetic is far from a thick oil. Toyota has done a dirty deed to their customers by demanding that 0W-20 be used, or the warranty is under threat. Ask a Toyota dealership now in 2017 to use another weight oil, and most simply will refuse to, regurgitating the same nonsense Toyota tells them - only 0W-20, and at 10,000 m. intervals. That is insanity. There are metal break-in shavings, and oil deteriorates over time, including synthetic, mostly from the byproducts produced from fuel combustion, which dirty the oil and filter, and are toxic to the engine.
The bottom line is: You don’t leave ANY oil in an engine for 10,000 miles, or you are greatly shortening the life of the engine. Furthermore, you shouldn’t use ‘water oil’ of 0W-20, but you are backed into a corner by Toyota, who is working against you, not for you. You literally have to find a dealer or a non-dealer shop to do your oil changes, and not print a receipt that shows they used anything other than 0W-20. You need to throw it right back at Toyota, and play games just like they do to protect yourself, as YOU are number one, NOT Toyota.