Actually since it's got just shy of 170k on it I could do whatever I want. But the fact that it's made it to 170k miles, not a single engine problem ever, does not use a lick of oil between changes, does not leak a drop, gets reasonable economy tells me something. Why try to second guess Toyota? Also the reason they require 0W20 synthetic oil is due to the VVTI system in it. Using something else can cause issues with the VVTI gears. Not gonna mess with success.I dont blame ya for not wanting to mess with warrenty, but i think the 3.5L (same as my taco) in other parts of the world allow whatever weight of oil suits the temps..... what reading ive done is these thin oils help with economy/emmissions. Ive ran T6 5w40 in my tacoma a few oil changes. Cant say i noticed any difference.