I took the jetta on a road trip from michigan to florida. The weather here has been in the 80's every day. Back home, they have accumulated nearly 20 inches of snow during the 10 days we have been gone.
Here are my fuel mileage numbers: Mk4 jetta 99.5 225k miles, Ipike snow tires over inflated by 10% (at 50 degrees F) Myself, my wife, our 7 month old daughter, and a car full of luggage. (babies and wives need A LOT of stuff!)
first tank of fuel: 55.0 mpg driving under 70 mph with winter diesel. 826 miles when the fuel light came on. Still had about 1.5 gallons left in the tank as i put in only 15 gallons. (ventectomy!) I don't often run my car below 1/4 of a tank and did not realize how much fuel i had left. I could have easily joined the 900 mile club!
2nd tank of fuel: 48.9 mpg driving between 75-80 mph with A/C on. Only 725 miles when fuel light came on.
3rd tank: over 2K miles of driving so far, and have yet to fill up a 3rd time...but mileage is pretty crappy this tank. Spend 6 hours stuck in traffic coming back from the space shuttle launch with the a/c on high.
I wish i had the patience to drive under 70 mph on the way home with a full tank of summer diesel, but i think i am going to be in too much of a hurry. It's about 1,400 miles from here to home.