[lear31a driver]

I have a couple of responses to address. First to the skeptic, I have a degree in Aeronautical Engineering with several advanced classes covering chemical engineering. I have run several advanced tests on fuel, and additives ( utilizing independent labs that specialize in fuel analysis ).. to further my own knowledge base as well as for optimum performance in engines that are designed to put out rated horsepower for hours on end. Some of these engines (piston) are rated in the excess of 1200 horsepower and are normally aspirated. If you were to place these same demands on your off the shelf M/B the engine would self destruct. I also have the hands on experience, tearing these engines down (including M/B engines) completely and using advanced tooling to determine wear and develop improvements.

Off the shelf cleaners don't really work unless you use them on a regular basis. This applies especially to fuel injector cleaners. Carbon and sulfur deposits build up over time and divert or restrict the fuel spray. This happens regardless of the fuel you use, including grade. I use a force feed injector cleaner in my shop that the consumer can get the same service at a competent mechanics shop. This forces under pressure (60-100 psi) a strong injector cleaner not heavily diluted with fuel. Cleaners introduced to the oil are bad, I never have found an advantage to using them. In fact, they often do more damage than good. I am a believer in regular oil changes (draining vs. siphon) and the use of synthetic oil such as Mobil 1.

Now for some personal experience. I previously owned a 2003 E500 with 165k on the clock. The new owner paid me to overhaul the engine and make some needed performance upgrades. I drove the car with a 50/50 city highway mix. I used regular fuel over 90% of the time. The only deviation was when I knew I would be going up long grades into higher altitudes (the Sierra's to Tahoe). Upon teardown, the pistons and cylinder walls were in fine shape. The spark plugs never showed glazing. The valves were all within factory tolerances and the seats weren't pitted or unusually worn.

Using premium fuel is a personal choice. You are right if you do, not wrong if you don't. Basically use common sense. If you try and get E55 results from a E350 .. use premium. Otherwise, take the money you save and put it into more frequent oil changes/maintenance.

Post note .. the 03 E500 motor turned out 385hp on the Dyno .. not bad for a rebuild.