Theoretically, yes. But with "multi-grade" oils (like 10W-40,) there are short-chain polymers in solution that combine as the fluid is heated - which resuts in the oil actually getting thicker - to a point - as it gets warmer, and running a bit thinner when cold (to help with cold flow on startups, and adhesion, cooling, and lubricity at operating temperatures.)
I know it doesn't make sense on the face of it, but it does when you think about it for a little bit - from an engineering point of view...
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