Originally Posted by PWGuy
Ok, an update - the tank was about half-emtpy at 103.3 miles. I filled it up last night to the FIRST CLICK ONLY and the amount filled was 4.940 gallons.
So I achieved 20.9mpg on the last 103.3 miles.
Now, I did take the car on a few extra jaunts around town out of necessity in the 103.3 miles without considering the affect on my test.
I also filled it with premium gas last night and the fill-up previous to last night.
Lastly, I removed the K&N filter from the stock airbox about 25 miles ago and added a Fram filter from Walmart.
Averaging just over 20mpg for primarily short cycle city mix isn't all that bad. Especially if you are running ethanol blend and the ambient temps are cooling off below 70 degrees. In my SVT with primarily highway on ethanol blend I average 25mpg. If I burn an entire tank at 70mph I get about 33mpg. This goes down to 30 at 80mph.
The fact is you may never average much better if you drive short trips with no extended run times above 55mph. Allowing the engine to warm will not increase your mileage necessarily but it will certainly extend the life of your powertrain... so you are kinda making a tradeoff between saving every drop of gasoline and keeping your rig in proper working order.