I used regular unleaded and my 1994 C180 goes alright though feels very under powered. Then I used premium unleaded and it feels better. Now I am using 98 octane premium and somehow, the engine feels odd, running a bit rough, power is there, but at higher speeds. At low speeds, it feels like the regular which is only 89 octane I reckon. The normal premium is about 94 here, any Aussies can correct me if I'm wrong. Sometimes I regret getting this car because the motor has very low power and I have to step hard on the gas. Then its got no 5th speed, so you keep stepping harder and harder to get along at 100kph or 110kph on the country highways. Whats making it worse is its winter now and somehow, the suspension which is unrelated feels a lot harder now than Summer??? . Maybe I should release some pressure or get the shockers up front inspected for total or close to total collapse!