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Everyone thinks 10w40 is thicker, but they are mainly the old type dino oils that use STP type additives to thicken.
Those additives make hard carbon, and I haven't heard of any for German hot running cars.
A Mobil 1 0w40 is same weight as it's 10w30 oil at 32 deg f, but the 0w40 doesn't thin as much as the 10w30 so it's thicker at operating temps.
Castrol makes a 0w30 that seems about as thick as Mobil 1 0w40, and also has a Edge 0w40.
I like 0w40's for modern long running synthetic oil 's.
The BMW 5w30 has operating temp weight of around 10 cst, and the Mobil 1 0w40 around 12+ cst so it's slightly thicker.
I'm running Mobil 1 0w40 for approx 10k miles even if not listed as BMW on bottle although I took BMW's free changes of 5w30.
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