My 1994 C180 Euro seems to be running better on regular than premium. Why I don't know. Besides saving on about A$0.05 to A$0.10 per litre, it makes the motor smoother with less vibrations when on "D" at idle especially at traffic lights. Less vibrations when I change to "N", but this is not necessary at traffic lights. Is it ok to run on regular or can I do full premium, then full regular and so on or just fill half of each every time??? Will this damage my motor which is only a 4 cyl, twin cam , 16 valve, fuel inj 1800cc motor? The car is only 1350kg kerb weight, but feels and looks like its 2000kg. The tyres are 195s on 15inch Benz steel rims. Your expert advice will be appreciated.