I think I am abnormal then if I get the best diesel mileage, my ghareeb VW diesel returned me 22 to 24 km/lit easily, the nissan CD17 I overhauled could manage the same - I couldnt find any petrol corolla doing that, my current mercedes benz diesel is 3000cc NA, and it can return me 15 km/lit.
How does your corolla diesel come out lower than your petrol one?