I've just bought a 99 E320 4matic wagon with only 83 thousand miles, 1 owner. The multifunction indicator suggests next service at 103K. Hmm. I don't know if there has been synthetic oil in this car, or if it has synthetic oil now. Dealer serviced. Would that be synthetic? Do you experts think I should use synthetic oil, in any case? MB seems to recommend it strongly in the manual. And while I am at it, should this old (since 1957) Mercedes driver break down and become a faithful user of premium gasoline in this car? Mason Smith

 

Oh, there are so many tales about synthetic causing seals to leak and never switching from non-synthetic to synthetic and vice versa, etc... Most of the oils available today are better than ever. Their lubrication and cleaning capabilities are excellent and in part this is the reason for which cars are lasting a very long time. The most important factor is that you change the oil at regular 3000 mile intervals or every 3 months, even if you have not driven the afore mentioned distance. If you live in very cold or very hot climates, the synthetic may offer some additional protection. Otherwise, conventional will do fine. I highly recommend Castol oil.

As for the gas issue, stick with premium. The car will run better. It is a fact that the anti knock sensor will compensate for a lower octane rating. However, with premium you may able to make up some of the cost difference, as it will require less fuel to reach the required combustion to move the pistons. Besides, when you fill up, the cost difference between the two grades is about $3-4.