It might not be a design flaw that would be picked up during testing. The clearances on these engines are so tight now that just one machine slightly out of tolerance could screw things up. They use 0w-20 oil for a reason. The tolerances are roughly 10x tighter than they were a few decades ago. That thinner oil is necessary to get into the tight places and flow properly. Toyota allowed 5W-20 oil to be used for 1 oil change during the pandemic when there were shortages, but they added a disclaimer that 0w-20 must be used on the following oil change. If you look into the detail of the 3.4 engine, they are using different bearing material than the 5.7. The 5.7 engine already require 0w-20 oil. I am only speculating, but I would bet the manufacturing could not meet the extreme tolerances required to keep the bearings lubed enough. It's even worse with a turbo engine and the extra stresses they have to deal with. Could I be wrong...sure. But I know that 2024's have had bearing failures. It's documented on other forums. Toyota is probably scrambling to figure it out right now. I hope Fightnfire is wrong that Toyota won't tell us when they do find out, but I suspect he is right. I like the idea of twin turbo, small displacement gas engine for the power. However, building them en masse may take an extra level of QA/QC that even Toyota hasn't prepared for at this time.For me, a design flaw would have been found during testing. They literally hook up engines and try to destroy them by starving them of oil and running them so hot it glows hot red for days.
A mixup at the factory? That's a whole heck of a lot more believable to me.
Also, this type of comment thread happens with all the manufacturers. Every time Ford/GM or Ram has a recall, the comments immediately go to design flaw. I just find that fascinating.