I had the same question about a year ago and read somewhere that with synthetic oil, the issue is to determine the minimum air temp in which the vehicle will be started, as well as the max air temp in which it will be operated, and to select your weight grade accordingly. My ML and I spend a lot of time in the mountains in the winter months, and I went with Mobil 1 0-30
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...Tracy
'00 ML320 "Casper"
'92 400E "Stella"
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