PeachParts Mercedes-Benz Forum - View Single Post - Will synthetic differential oil give better fuel economy?

Jeremy5848 · #9 11-24-2010, 11:56 AM

Because synthetic oils are made to have smaller molecules (this is why they have better cold-flow characteristics) they will leak out of tiny gaps that dino oil won't. When I put Mobil-1 synthetic diff fluid in my '85 300D-T (W123, OM617), it would drip one drop of fluid every few months. The diff cover has no gasket, you know, and sealing depends on the metal surfaces plus whatever sealant you put on them. There might be some advantages in extremely cold climates but I don't see any improvements in fuel economy measurable by normal drivers.