Yep, needing real heavy oil in hot temps is an old wives tale left over from the days of dino.

5w-40 is just fine for year round use. Heck GM runs 0w-20 in a bunch of their engines, and MB factory fill has been 0w-40 for years.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200