oil viscosity question

her manual says 5w30 and i told her to buy 5w30 but for whatever reason she looked it up on mobil’s website and is asking me why they say 5w20. she doesnt even use mobil 1, she uses castrol syntec i think.

Grab her by the throat and tell her ur gonna use 5w30 and shes gonna like it.
WTF?! My gf has done that before…its like do it yourself then.
Sorry, my rant is done.