I have owned the M6 for the past year. Realising that the fuel guage when at full, takes about 100km to 120km before it drops to half level between F & 3/4. By which time I clocked mileage of 170km - 200km it would reach 3/4 mark. Depending on usage, sometime I encountered only 90km the moment the guage pointed at 3/4. By which time, I reckon the guage reach 1/2, mileage clocked would be hoovering around 240km-300km. The moment the guage showed below half, it drops tremendously with almost every 20km I travelled. By which time it reached the 1/4, usually I would have clocked around 420km to 480km. What amazed me was-when traffic jam, sometime the guage could rise about 10-20% (I suspect due to evaporation of the gasoline)-giving false impression that there was sufficient fuel.
I managed to drive till the fuel guage warning light appeared to exactly see how much a full tank could cover, I realised at time-could take 570km below the 1/4 mark. The record mileage I managed was 620km just when the warning light illuminated. I tested it using same grade fuel & same pump price.
I was sure the fuel guage in the M6 is air tight plus the fuel cap was securely fasten. But to date, I am still puzzled why the fuel guage is so inconsistent.
Fortunately the M6 is equipped with the fuel per mileage cover on the display panel to check if fuel could cover desired distance, if not some time I found hard to determine how accurate the reading could be.