All of the oil charts I have seen end at 86F. all 40W and 50W oils just have an arrow past 86F. My question is, at what temp is one supposed to switch from 10 or 15-40 to 20-50? it seems to be too cold in the summer mornings in CO for 20-50, but alot of people have told me to use that in the summer, which is fine when it is 90F but not so good at 60F.

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Will
94 E420
82 300DT
77 F250 4x4 429 Cobra Jet
69 Thunderbird 429 Thunder Jet
92 Mitsubishi Galant VR-4