My C320 requires premium fuel but a few years ago there was such a price spread between premium and mid-grade that I thought I'd try it. I didn't notice any real difference in power and don't recall whether there was a drop in mileage or not. Since the M112 V6 has knock sensors, they would hear any detonation before I did anyway and retard the timing. But, the timing is retarded only until the detected sound goes away and normal timing is then restored almost instantly. This is done on per-cylinder basis. Turbocharged (and supercharged,, perhaps?) gassers also reduce boost at the same time and have done so for more than twenty years but that effects the entire engine.
I mentioned to one of our local factory reps that I was trying mid-grade and he said that when warm weather returned I should go back to 92 octane. Speaking of M112 V6s, I dropped in to the dealer yesterday to make a repair appointment and drove into the shop to have my "personal" MB tech order the parts and I saw an M112 block on the engine stand with a sizable hole in it's side. Laying nearby was a connecting rod twisted in two at the midpoint. Seems that during our Wet Period recently, the driver of the vehicle from whence the parts came didn't appreciate the significance of the bow wave of water in front of his car. Even after the "noise" and the car came to a halt, he restarted it to drive to shore. I imagine the sound of the lower half of a connecting round spinning around in there might continue to be "noisy." Inhaling a quantity of water into the intake resulting in hydrolock is to be avoided. His insurance will pay to repair, not replace it due to the $14K cost of a crate motor. The crankshaft is thought to be bent, also. RLE
