Our manual says we have a 19.5 gallon tank. I don't think 17.5 gallons is going to cause an issue

 

He might have some left in the tank as well. I've always heard the light comes on at 16 gallons, gives you a 3.5 gallon reserve.

 

yeah but your tank isn't bone dry i bet.

 

If you're trying to tell the difference between 10 MPG and 20 MPG, that will work, but if you need precision, then first, you need to fill the tank exactly the same way both times, perhaps using the same pump handle (some pumps will put a little more gas in than others). It also won't work if you have one leg of a trip on it that involved either an elevation change or prevailing winds.

It's better if you keep track over multiple tanks. So do 10 tanks of gas and divide by the total mileage over that period.

When y'all put bigger tires on do you re-calibrate your odometers? If not, that will make it seem like you're getting lower gas mileage than you really are. Hit the trip button when you drive past a mile marker on the interstate and see if you're rolling past another in 10 miles as the clock rolls to 10.0. If not, then make a note of what it says, and you've got a conversion factor for future reference. If you go from a 28" tire to a 31" tire, you'll cover 10% more distance with each turn of the tire, but the odometer won't know it.

 

This is what I do to calculate mine. It might be a little off but it gives me a pretty good idea of what I get, how much I spend, how often I get it and I can see the changes in the price of gas. lol

 

Wirelessly posted

Looks like you don't drive much

 

wow that is some spread sheet.


well, I just checked my milage for the first time since cutting of my last cat and putting on the exhaust system. With 90% highway driving I got 21.49 mpg. Also, I didnt recal my speedo after installing the 32x11.50s either

 

About 12,000 miles a year. I stopped doing the spreadsheet a few times so its not there for a whole year. You can see the mileage difference and the dates, thats where I skipped.

 

Here's what mine looks like. I actually just have a little notebook in the truck that I write my gas purchases, plus any maintenance into. I only type up a spreadsheet on occasion to see how it's doing. It's more a way to remember when I change the oil than anything.

The second set of calculations, on the right, is a rolling average over two tanks of gas. When you do that, it smooths out the measurement error, and minor changes. You can see I got between 20 and 21 MPG in March. For the whole period I drove 2422 miles on 118.19 gallons -- 20.5 MPG overall.