I got only 14-15mpg on my first couple of tanks, although I did vary the RPMs quite a bit using sport mode during the engine break-in process. After about 1.5K miles, I've been consistently getting about 16-17mpg in city driving, and 21-22 on hwy. My last tank I squeezed out 370miles (70% hwy/30% local) on 18.5 gallons for an even 20mpg.

To the OP, do you idle alot? You will see that excessive idling has a big effect on mpg. I left it running for 1/2 an hr once and it brought my overall mpg down by close to 2 for the tank, when I had more than 200 miles driven already.

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11' X5 35i Sport Activity - AW/Blk/Alum
06' Subaru Legacy GT - GONE
05' BMW X3 3.0 - GONE
01' Honda Prelude, modded - GONE