I use Mobil 1 15W50 year round in this naturally-occuring sauna that we call Louisiana, and I have nothing but good things to say about it. I change it every six months, as the 300D is only driven about 6 or 7 thousand miles per year. I used to lose (use?) about 1/2 quart per month when using dino oil. I last changed the oil in December, and I've lost less than 1/2 quart in the last 5 months! As for OM617 oil capacity, I think it's 6 quarts, but it may be a little more. I buy Mobil 1 in 5 quart jugs at WalMart for about $20.

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1982 300D, black w/ palomino leather, 203K
2001 E320, champagne, 105K (Mom's)
1999 Dodge Dakota, squeaky & battered, 142K