There are two basic types of auxiliary tanks: in-bed and underbody. One advantage of an underbody tank is that it doesn't take up any space in the cargo bed, as is the case with an auxiliary tank. The latter also may require extra plumbing and valves for switching between two tanks. On the other hand, you can add a pump-out nozzle to an auxiliary tank in the bed, which is an advantage for a customer with other diesel engines that might require refueling in a remote area.
Aero Enterprises makes replacement tanks for every domestic make of truck as well as tanks for toy haulers, RVs and all sorts of custom applications. Instead of plastic (used by vehicle manufacturers), Aero fabricates its underbody tanks from enamel-coated, aluminized steel with internal baffles, a drain plug and through-bolted steel mounting tabs. (Plastic tanks typically are secured with metal bands that can rust or trap debris that chafes against the outer surface. Also, plastic tends to swell with changes in temperature, which can lead to leaks around the fuel pickup.)
The application shown here was on a 1996 Dodge Ram, which required some custom work in order to clear the mounting plate for a Gear Vendors gear splitter. For a modest extra charge, Aero can provide a custom-welded tank with a recessed area for extra clearance, if needed. Even with this modification, the tank capacity went from 36 gallons for the stock unit to nearly 60 gallons in the underbody tank.
The 12-valve Cummins in this truck typically consumes 19 mpg on the highway, so that's more than a 1,000-mile range between fill-ups.
Here's one other point to consider when changing out the tank on this particular make of vehicle. The sending unit on the fuel pickup assembly on older Dodges is known for wearing out as soon as 40,000 miles or so, and that was the case on this truck. Remembering to reset the trip odometer at fill-up time (in order to estimate the fuel level by miles traveled) was getting annoying, so we were really glad that Jake Jacobs at Aero swapped out the sending unit with a newer type made of a more durable material.
Jacobs points out one difference in the gauge readout after upgrading to a larger tank. The fuel needle will stay on full for the first 15 to 20 gallons, because Aero uses the factory fuel pickup and does not make any adjustments to this part. So while your customer is not actually improving your fuel efficiency, it at least seems like they're getting more miles to the gallon!
Steve Temple is a freelance technical writer and photographer with more than 25 years' experience. He has served as director of sales and marketing for Shelby American and as online editor for major magazines such as Hot Rod, Car Craft and Rod & Custom.
