Quick question about thin motor oil, specifically xW-20

[2EHA]

View attachment 90401
This is what Toyota recommends for the fj cruiser 1GR engine .
can someone explain how 5w30 is not ok but 10w30 is? they both have the same hot viscosity .

lack of trust in historically terrible middle eastern oils

 

[ssaaff]

lack of trust in historically terrible middle eastern oil

Maybe, but can you say the same about Australian oil since they recommend the same thing ?
I think heat is the killer here

 

[OVERKILL]

Maybe, but can you say the same about Australian oil since they recommend the same thing ?
I think heat is the killer here

Since Toyota doesn't have an oil spec, they have no guarantees other than the basic API stuff as to stay in grade. Historically, that has not been very rigorous, so it makes sense in that context that, in climates where the lower Winter rating isn't needed, to just avoid it.