18 mpg for a 1.8T is really low. Get it on a VAG to see if everything is working within specs.

 

I only get about 19 but its on a 2.8, so yours seems pretty low

 

I can't even check mine because of those missing pixels!!!

 

You can fill up your tank, reset your trip guage and when u fill up your tank just take the gallons you filled by the miles you drive

 

Mine gets 16-17 mpg city, and about 23-27 highway. I hate the poor fuel economy since I don't drive on the highway often. I'm due for a tune-up in 3 months....

 

My 2.8 gets better than that even when hustling it around.

Change the spark plugs, change the air filter, change your fuel filter.
Run 93 octane WITHOUT ethanol. Ethanol sucks man and gives you worse mileage.

I changed my plugs and stopped using ethanol and immediately picked up 2-3 mpg. Doesn't sound huge, but its almost another 50 miles to the tank which adds up.