I've always taken good care of my cars, and right now I'm driving a 1997 Mercedes C280. In the past I have always used nothing but premium gas and I just wanted to be sure that this is the right thing to do with the C280. A lot of people are saying that it's not necessary to use the higher octane.
First thing to do is check the manufacturer recommended octane rating for the particular engine. The 2.8-liter straight-six in your C280 is supposed to run on a 91 or higher octane fuel. The octane rating of gasoline with the Premium name tag can vary depending on where you buy it, but you certainly are in the right ballpark.
The octane rating of fuel is a unit of measurement on a scale intended to indicate the point of detonation or knock. This is the sound produced from a non-uniform burn in the combustion chamber, and this can produce permanent engine damage.
There are several variables that determine which engine needs what octane fuel to run efficiently, without producing a knock. The compression ratio is a major factor (compression ratio determines pressure within the combustion chamber). Mercedes uses a slightly higher ratio than most non-performance passenger cars, and therefore will require a higher octane fuel.
The majority of cars sold in the U.S. can run on their recommended octane rating of 87 without producing a knock, and this is what a lot of drivers want in order to save cash at the pump. However, staying a step ahead of the minimum octane rating to get the best performance and avoid the damaging knock couldn't hurt. For example, using 89 octane in a vehicle you care about which has a recommended rating of 87, is a safe way to go. But using 93 octane would be unnecessary and produce insignificant gains.
See what I mean?