All oil temp charts I have seen end at 86F. What are the upper limits of the oils that max out on these charts? What temp should one switch from 10-40 to 20-50? I bought my e420 in Vegas, it came with 20-50 which seems to be to thick for 50 degree mornings in CO.

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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