I think 20mpg+ is possible, if my calculations are correct.

My estimate is based on a stock 05 X with 6-speed manual tranny, 4x2, driving in Southern California winter weather (where its still relatively warm ), mix of city/highway miles, but mostly city.

Simple method I use to calculate mpg:

1) fill up the tank
2) set the trip odometer to zero
3) the mileage gauge is divided by 4 sections by the tick marks, each section equal to 5.25 gallons of fuel. (21 gallon tank/4 = 5 gallons gas per section).

4) Note the trip odometer reading when the needle reaches the 3/4 full tick mark, then divide that reading by 5 (or 5.25 if you want to be more precise) to get your mpg.

In my case, the trip odometer read 110 miles when the needle on the fuel gauge rested squarely on the 3/4 mark.

Dividing 110 by 5.25, gives me close to 21 mpg.

If this result holds up for the remaining 3 sections of the fuel gauge, I will be a happy camper.

So how far can you drive while the needle is still on the full mark? ahhhhh..... now thats good gas mileage there.

That's a guesstimate - and, methinks, wishful thinking. The best way to get your actual mileage is to fill the truck, then note the exact miles driven at your next fillup along with the exact gallonage needed to fill up again. Divide the miles driven by the amount needed to fill up and that's your actual mileage. It's likely to be less.

Every notice that the top half of the fuel gauge goes down slower than the bottom half. The 4 marks on your gauge are not incriments of of how many gallons you have left. It's how full the tank is and all tanks are shaped differently. You burn through the top half of the tank slower than the nottom half.
As far as a K&N filter. I have one on my Talon, made no difference, I have one on my CBR...no differnece. Get a K&N for the re-usability and cost savings in the long run, not if you expect any performance increases.

I've read all the posts, and have to offer my thoughts. My 2004 Xterra consistently gets 16-18 mpg with no modifications. I live in a rural area and drive local roads at 55mph and the interstate at 65mph. The only time my mpg drops is when I drive in 4wd due to snow and/or ice. I usually use Shell gasoline, kkeep the tires at 32psi, and stay off the gas pedal unless it is necessary. The engine is a workhorse, not a jet engine. Just my .02...........

Its hard to get an accurate reading of average mpg on even one tank, as there are so many variables...but if your habits are very consistant, you can at least get a guesstimate.



The BEST way to get real average mpg...which accounts for the differences in top off, etc...is to pick a long term mileage goal, or a ten fill-up cycle, etc...

Ten fill-ups is the easiest to track.

Filler up, note the start mileage, say 30,000. (This is not fill up #1, this is zero/starting point)

At each fill up, note the new mileage, and how many gallons you took.

When you are done with fill-up #10, add up all the mileage (Difference between the zero/start mileage and the end mileage on the #10 fill-up)

Then, add up alll the gallons pumped into the truck in fill-ups #1-10.

Divide the total miles by the total gallons...and that's a good estimate of your mpg.



Also - Huge issue....if you've upgraded to larger diameter tire...you've probably been speeding, as the speedometer told you you were going 60 when you might have been going 70, etc (My speedo for example...)....which KILLS your real mpg.

AND

Your odometer will be off by the same proportion, so your odometer might say you only went 3,000 miles, but you might have ACTUALLY driven more like 3,510 miles (My odometer...)....which KILLS your APPARENT mpg.

I know a guy with a 2001 V6 manual, it's a 4x2 and on the highway he gets around 22 MPG. In the city 18-19 MPG consistent. He drives like an old man.

My 2001 V6 Auto 4X4 gets around 14 MPG with 32X11.50 tires at 59 Lbs. each I weighed one because it is on the roof. I also tow a 20 foot travel trailer that weighs 5200 lbs. loaded and the Xterra does 65 MPH tops with a K&N Filter and a Magnaflow Stainless muffler. MPG with trailer 11. Not bad for the size of the trailer. I had a custom 10,000 lb. hitch installed with 1,000 lb. tounge weight and the Xterra handles it fine. The VG33 engine is a workhorse not a race engine.