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Originally Posted by Brian Carlton
I too like the extended drain intereval with the synthetic. I run Rotella T synthetic, at $13.00/ gallon, and I change it at 5K miles. Now, oldnavy, I have to disagree with attempting to go more than 8K with a 617 engine. I did that one time. I had the oil tested after that 8K run and, although the additive package was fine, the soot levels were definitely elevated. Since soot is an abrasive, it would be foolish to attempt to go 10K or more with any oil in a 617. The 616 is similar.
Since I feel the need to change every 5K due to soot levels, it does not make a whole lot of sense to purchase the better Group IV synthetics.
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Some important points to keep in mind:
1)
Every engine produces different amounts of soot. The only way to tell how much is to test YOUR engine. Don't attempt extended drains based on other people's data! My 603's make about 1% per 10kmi. My 617 makes about 1% in 2500 miles. Your engine type, driving habits (lead foot?), and conditions (stop & go?) affect this a lot.
2)
Different engine oils can suspend different levels of soot. I believe Delvac-1300, Delo 400, Delvac-1, and Mobil-1 5W-40 can all suspend at least 4% soot. The other Mobil-1 varieties (of which 15W-50 is the preferred choice for MB's) can only suspend 2%! You need to change the oil before you reach that oil's soot limit.
3)
Mercedes has recommended not exceeding 2% for MB diesel engines, especially for engines with hydraulic lifters. (That just means I should change my 603's oil at 20kmi/2% with Delvac-1, instead of the ~40kmi/4% which the oil is able to suspend.)
4) Side note on Group III synthetics. They appear to shear down more quickly and then the oil consumption increases, making them a poor choice for extended drains. They are probably OK for standard intervals like Brian is using. My Group IV/V oil lasts twice as long, which offsets the cost. BTW - the Rotella Syn is ~$14/gallon ($3.50/qt) at Wal-Mart, while the M-1 15W-50 is $19/5qt ($3.80/qt)... that convinced me to ditch the Group III stuff permanently, at least given that pricing!
