I have a 2004 Dakota 3.7 V6 4X4. On the build sheet it says it has a 22 gal fuel tank. When I fill it up from empty it only takes 15 gals. The float assembly has been changed by Dodge dealership and it still only takes 15 gals. Any ideas as to why.

 

Have you had it since new? May have had the tank swapped out.

The 22 gal tank is something along the lines of 60" long and a 8x12 cross section I believe. It was damn close to my wingspan when I was carrying it by the built-in handles.

 

Dodge also left a 'reserve' in the tank. When the gauge hits empty, there can still be several gallons of gas left in there.

 

Most I've ever got in my 24 Gal tank is 20 gallons. Usually filling it long after the light has turned on, I get about 17-18 gallons in it.

 

My '98, per the build sheet, came with a 22 gal tank.
Visual and usage experience confirm that.

The low fuel warning (ding & light) comes on at about the 1/8 tank mark.
When the gauge needle reached empty and no longer can be made to move, I still have at least 3 gal in the tank.
It will take 19 gal to refill.
I can still get 45 miles at 16mpg and not run out.
It takes 21 gals to refill from there.
That's as far as I've pushed it.

From when the needle reaches empty and no longer moves, I am able to assume that I still have 3 usable gallons still in the tank.
That is my "Get your act together or you're in trouble" point.
Been using that for years.
I do occasionally worry about age changing how the gauge reads, though.

 

If it really bugs you, fill the tank full. Put a 5 gallon can of gas in the back. Reset the trip odometer, then drive till you run out. Note the miles traveled. Put in the 5 gallons, then go to the nearest gas station to top off, remembering to add the 5 gallons to the total top-off minus whatever the distance to the gas station from your run-out location divided by your mileage shows the gallons burned to be. Now you'll know how much your tank holds, and how far you can drive on a tank. Going forward, reset your trip odometer every time you fill up, and use that as a gas gauge. Really I'd suggest that you just keep going as you are as several gallons in the tank will keep the fuel pump cool and help extend its life, but if you really want to reduce gas station stops just fill up about 50 to 100 miles before the run-out distance.

If you want the fuel gauge to more accurately reflect when you're almost empty, pull the pump and bend the float arm down so the bottom of its movement is closer to the bottom of the tank. Make sure you put bending force only on the steel rod, don't let any reach where the rod connects to the pump because it's easy to damage. Bending the float arm down will mean the gauge will take forever to come off full, perhaps half your driving range, but when it shows empty it'll be sucking fumes. Don't go all the way to the bottom though, or you'll run out before you hit empty.