Where's the "gamble" it's well established that the difference between 20 grade and resource conserving 30 grade is next to nill, the only way you'll damage an engine running oil thicker than specified is if you do something blatantly stupid like put straight SAE50 or 25W60 in a car in the dead of the northern winter and floor it hard while it's cold.
Thanks for the input. You are entitled to your opinion, but I stand by to mine.You will get a much wider swing in viscosity between morning and afternoon starting temps. I honestly don't think many people comprehend how much oil viscosity (even of multigrade) changes with variation in temp. The difference between a 20 and 30 Grade is miniscule in comparison.
As as long as the oil has the required pumpability for minimum temps and the required minimum HTHS for the engine design and oil temps I don't see it as a gamble at all.
Putting 40 Grade in your car in a Death Valley Summer or a 0W-20 in a car in a Wiseman AK winter is unlikely to be an issue just because a car has a 5W-20 or 5W-30 oil cap. My car says SJ on the oil cap and I don't use that either.
My Jaguar requires 0W-20 and I will keep it that way.
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