Originally Posted by Jammer
1) With proper planning, is a 35 gallon gasoline tank sufficient at the 9-10 MPG towing that seems to be realistic with larger trucks and trailers? If not, is a ~15 gallon increase in capacity sufficient?
2) Is the availability of under-bed replacement tanks of higher capacity, and the slightly higher MPG, for diesel trucks a reason to consider them? (I am, in general, not a true believer in diesel engines)
3) More broadly, how much cruising range is necessary?
1) This depends how far off the beaten track you like to get, and how much you tend to anticipate things. Most people don't like to do more than 200 miles or so at (CA) legal towing speeds w/o a stop; if I expected everyone in our truck to make it between needed fuel stops I'd have outright rebellion on my hands
. Out here in the West I've never had trouble finding diesel, but I do tend to not wait until the second tank is nearly empty before discovering we need fuel.
2) The reasons to tow w/ a diesel is because of the very flat power curve, overall longevity and that it will happily operate at high output w/o fuss for hours. Our '96 F250 makes 200+ hp from 2000 to 3400 rpm; this means that as the RPM drops under load the torque climbs proportionally. As a result, the truck pulls hills very easily, and will operate at WOT for as long as needed to climb steep hills. I'm never worried about the engine; the transmission on the other hand has a hard life when towing. Fit a transmission temperature gage if you tow in the hills.
3) Most people find the stocks tanks sufficient. I'd follow 2airishuman suggestion and use one (or two) 5 gallon yellow diesel cans in the bed until the answer for your situation becomes obvious.