Not quite.
A more basic base oil would need more VII's to stay in grade, but generally 5w40, 5w30 0w30 etc are fully synthetic with a more stable base oil, and, importantly, better quality VII polymers thus are very stable. Also it isnt about staying in grade when hot, its shearing dowm to lighter 'weights' due to the vii's becoming 'broken', this is why you avoid cheap oil and/or wide ranging semi's.
So no, a 10w40 isnt more stable than say 0w40, but a high quality 10w40 might be more stable than a cheap/semi 5w40. A cheap 10w40 would be less stable than a high quality 0w40.
Basically, avoid cheap oil, stick to the big names, use the right spec. 👍
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