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All 3 spec 5w20 because they believe it takes a minimum 5w oil to make the system work correctly. If you use 0w20 you may be fine but maybe not.....
This claim makes no sense to me. There is a minimum oil viscosity and a maximum oil viscosity with which the engine can operate properly and reliably. The only thing a 0W-20 does relative to 5W-20 is extend that range to lower temperatures.
Yes, true. Makes sense that a 0w20 does everything that a 5w20 does, and more.
But Toyota also waffles on the topic, suggesting in their TSB regarding the change to 5w20 that 0w20 was acceptable in only certain engines that were designed for it. Other engine designs that apparently required no changes or only minor changes, got 5w20.
Makes no sense. Unless the manufacturers are convinced that the 5w20 SM GF-4 testing standards produces an oil that is superior to 0w20 is some way.
To me, that is possible. They are loath to use the word synthetic, and yet it is clear that good quality 0w20 oils must probably be sythetic. (and probably most good 5w20 oils are some variety of sythetic or semi-synthetic as well, right?)
My guess is that, as logic would dicate, equal quality 0w20 oil is fine for an engine specing 5w20.
But remember the first wide range oils? The one's with modifiers that turned to sludge or wax? Perhaps manufacturers are justifiably hesitant to go in that direction, especially when the track record of the current crop of 5w20 oils seems so stellar......