Written by:

David Hosea

Last updated: November 1, 2023

My wife and I are full time RVers and we pull a 30 foot Airstream Classic that weighs roughly 9,000 pounds.  We don’t expect great mileage, of course, so we were prepared to stop frequently for fuel and simply wrote off the delays as the cost of doing business. Then, we started looking for a way to increase the time between fuel stops.

If the load and tow vehicle’s miles per gallon do not change, how do you increase the tow vehicle’s range?

If there are no significant changes to the gross combined vehicle weight and the fuel efficiency of a tow vehicle, increase the tow vehicle’s range by replacing the stock fuel tank with a larger one.

Fueling

Our 31-gallon fuel tank allows us to wander about 275 miles down the road before stopping for fuel while towing.  We can go farther when not towing, of course. Our overall length is roughly 52 feet, so we fill the diesel tank in the truck lanes at truck stops.  There are advantages and disadvantages for us to stop there.

First, we tow with a Ram 2500 diesel and the truck lanes have fast flow nozzles.  So, we can fill up faster in a truck lane than we can at the auto island.  That assumes that we can fit and maneuver through the auto lanes, of course.  The downside to fueling in the truck lanes is that we often have to wait in line a long time before getting to the pump. 

Tractor-trailers can take a long time to fuel.  The tractor can hold up to 300 gallons and even with fast flow nozzles, it can take a few minutes to fill them.  If the driver needs DEF (diesel exhaust fluid) or if they are pulling a reefer trailer that also needs diesel, it can take a long time for a truck to clear the pump. 

Common courtesy in the truck lane is to pull your rig past the pump when finished fueling so the person behind you can pull into the pump and start filling their rig.  It is common to see a line painted in the parking lot so drivers know where to stop.  From there, the driver will park the tractor-trailer and go inside to get their receipt, buy snacks, take a bio-break, and take care of any other business. 

The entire process for one truck can take quite a while.  When there are a couple of trucks in front of is, it is not unusual for us to spend up to an hour at a truck stop to fuel.

Travel Day

We travel using the 3-3-3 rule, which is like the trifecta of travel planning – cover no more than 300 miles in a day, arrive at your destination before 3 pm, and stay for 3 days. It’s like the travel version of “Goldilocks and the Three Bears” – not too much, not too little, but just right.

With a tank that limits our range to about 275 miles, we can expect to fuel twice on a travel day.  With up to an hour at each stop, a lot of our travel day can be spent waiting in line and it can threaten our arrival target of 3 pm.

The thought of replacing our stock 31-gallon tank with an aftermarket 52-gallon tank didn’t cross our minds at the beginning of our full-time adventure.  We looked forward to frequent stops at first because we could take bio-breaks, grab breakfast burritos and coffee, lunch and snacks, and stretch our legs. 

The frequent stops are not as appealing after a year of experience. Now, we have a problem to solve.   

Options

How do we increase the fuel-carrying capacity of our tow vehicle and reduce the delays in our travel day?  Our options include:

1. Install an auxiliary fuel tank:  This is a second tank that can be mounted in the bed or under the chassis and transfers fuel to the primary tank as needed.  Gravity feed tanks will allow fuel to drain into the main tank and will keep that tank full until the auxiliary tank is empty.  Auxiliary tanks with a pump will transfer fuel on demand.  Flip the switch on the auxiliary and watch the fuel gauge go back to full on the primary.
2. Use a fuel bladder: A fuel bladder is a flexible and durable bag that is carried in the truck bed.  Bladder sizes vary, but all take up space in the truck bed.
3. Carry a few extra gallons in Jerry cans:  Jerry cans are good when you need to extend your range on occasion and are cheap when compared to the cost of buying and installing auxiliary fuel tank systems or bladders.  But you have to find a place to carry them.
4. Replace the stock fuel tank with a larger one: A larger fuel tank fits in the same general space as the stock tank.  After market designs are different so expect a larger tank to take up more room front to back and/or top to bottom. They take up no space in the bed.

We planned routes through southwest Texas and New Mexico and assumed that there would be long stretches of highway where diesel was not available, so we carried two, five-gallon Jerry cans for several months as a reserve.  There were a couple of instances traveling along that route where we needed to transfer fuel from our reserve, so carrying the cans was the right choice.

Jerry cans are nice to have, but they are inconvenient.  They weigh between 35 and 40 pounds when full and must be moved from the bed, then hoisted high enough to drain the fuel into the tank.  Our Jerry cans got dirty over time and they sometimes leak a bit, so I had to wash up after refueling.  Transferring 10 gallons of fuel takes a little time so our travel was still delayed. Jerry cans take up room in the truck bed and because we travel full time, space in the bed is a valuable commodity.

Our Choice

I wanted to create more space in the bed and reduce the number of extra fuel stops so, we chose to replace our 31 gallon stock fuel tank with an aftermarket 52 gallon tank (I assume 48 gallons of usable fuel).  Auxiliary fuel tanks and bladders were non-starters for me because they take up too much space in the bed. The benefits to replacing our stock fuel tank with a larger one includes:

1. Extended range: The larger tank extends our range while towing from about 275 miles to 450.  When we spend a couple of weeks in one location and are not towing, our range will be over 800 miles.
2. Avoid unnecessary delays:  We decreased the number of passes through truck stops, spend less time overall waiting in line to fuel up, and spend more time on the road.
3. Saves money: On long stretches of highway with few truck stops, there will be little to no competition between facilities.  So, prices are often higher than in more heavily populated areas.  With a longer range, we have more choices and we can find a station with better prices.
4. Increases available space in pickup’s bed:  Removing two Jerry cans opens a small space that can be used to store other things, or nothing at all.  It reduces the clutter in the back of the truck.
5. Peace of mind: We don’t worry about running out of fuel.  Jerry cans provide a reserve when we need fuel in the middle of nowhere, but a larger tank gives us enough fuel to get to the next station, even if it is miles down the road. 

There are cons to replacing a stock fuel tank with a larger one.  They include:

1. Added weight:  A larger tank adds weight and reduces the amount of weight I can carry, but the difference is not significant.  Adding 21 gallons of fuel carrying capacity adds only 147 pounds to the gross weight.  The added weight also adds strain on the suspension and may reduce overall fuel efficiency.  It could lead to higher maintenance costs.
2. Cost:  The fuel tank and installation costs are optional expenses.  There may not be added expenses for extra hardware like support straps or sending units, but there can be.  Some tank replacements are plug and play meaning that existing sending units are removed from the stock tank and installed into the new one.  But, some tanks may require fuel pump or sending unit replacements as well.
3. Filling up: Filling up the tank will happen less frequently, but each stop will cost more. Some pumps at the auto-island side of the station will stop pumping after a set dollar amount. Some will stop after a gallon limit is reached. Either way, two transactions may be required at the pump to completely fill the tank.
4. The Distance to Empty (DTE) or Time to Empty (TTE) readings on the instrument cluster may not be accurate.  As of this writing, there seems to be no reliable way to change the tank capacity in a Ram Heavy Duty truck from 31 gallons to 52.  Ram requires a proprietary application called AlfaOBD to change the fuel tank capacity so DTE is calculated correctly.  However, results seem to be inconsistent.  Some reviewers report that the fuel gauge becomes unreliable after reconfiguring the truck’s computer with the larger tank.

Distance To Empty (DTE)

The Distance to Empty algorithm calculates how far you can drive based on fuel level and driving patterns.  But the mileage displayed is an estimate and changes quickly.  I often compare DTE to the distance remaining on our trip and assume that I will not need to stop for fuel because my range was more than 100 miles farther than my destination.  Then over a short time, I watched as the DTE range fell below the mileage to my destination.

My tank’s manufacturer pointed out that if I use my stock sending unit, my fuel gauge will report correctly.  Since I don’t rely heavily on my DTE, I chose not to attempt adjusting the tank capacity in my truck’s configuration.  I’ll continue to monitor my fuel gauge just as I did before the tank replacement.

Wrapping Up

Upgrading to a larger fuel tank increases our range on travel-day.  It reduces the time we spend in line at truck stops and gives us more choices on where to stop.  The downsides related to cost and weight are not an issue for us.  

Anyone that spends a lot of time on the road should consider how much easier travel will be with a larger fuel tank.  If you want to spend more time enjoying the journey, consider replacing your existing fuel tank with a larger one.  

See you down the road!

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