Which Aux Gas Tank

[Cal2121]

I have a 68 F-250 CS that came with the in-cab and aux tank under bed (driver's side inside frame rail). Based on my research, the aux tank is either 25 gallons or 17. The tech info says it should be the 25 gallon aux tank unless its body code 84 or 85. I'm not sure how to tell which tank I have. Any help is greatly appreciated.

[Bill Ramsey]

How many gallons does it take to fill it?

[Cal2121]

Great question. My fuel gauge is off so that when the tank is full the gauge shows a little under 3/4. The lowest I ever take it is to the last tick mark/line on the gauge (i.e., it never gets between the line and the "E"). I wasn't sure if that last mark meant it was almost empty and I don't want to run out of gas. But, if I run it down to that last little line, it takes about 17 gallons.

Thanks again.

[colnago]

What engine do you have, and how many miles between fill-ups? My 352 gets ~10MPG, so my in-cab tank usually gets a refill after 160 miles or so. Depending, you might be able to use info on your truck for a SWAG.

Joseph