Petrol/gasoline. I won't go into too many details (to avoid politics) but basically, our gasoline , which should be premium octane, (90 - 95) is actually lower than regular. When my mechanic cleaned the gas tank about 3 months ago, it was black. We're basically running our cars on kerosene.So my query would be what ruined the piston??? They're connected to the crankshaft and have rings around them so they're not supposed to touch *much*.