Adding an auxiliary fuel tank is a top upgrade for any off-road or long-haul rig. This is more than just bolting a new tank to the frame. You’re integrating a major component into your truck’s fuel system, so it must be done right.
A correct installation frees you from the constant hunt for gas stations. It massively extends your rig’s range and your freedom on the trail.
Getting a Handle on Your Fuel System Upgrade
Before touching a wrench, understand what you’re getting into. This isn’t just about carrying more fuel. It’s about safely integrating a new part into a complex system.
Your first decision is what kind of setup is right for you. For instance, a simple transfer tank is a separate container. You must manually pump fuel from it to your truck’s main tank.
This is a straightforward approach but not very convenient. On the other hand, a fully plumbed-in auxiliary system automatically feeds your main tank. This set-it-and-forget-it option requires a more involved installation.
Comparing Tank Materials
The tank’s material is another huge factor. It affects everything from weight to durability. Most tanks are made from one of three common materials.
- Aluminum: This is a popular pick because it’s lightweight and won’t rust. If keeping your rig’s overall weight down is a priority, aluminum is a great choice.
- Steel: For sheer toughness, nothing beats steel. It offers the best impact resistance, which is a massive plus for serious off-roading where your tank might take knocks.
- Polymer (Plastic): Modern polymer tanks are completely corrosion-proof. They can be molded into unique shapes, making them perfect for tucking into tight spaces.
The global market for auxiliary fuel tanks is expected to jump from USD 1.2 billion in 2023 to USD 2.1 billion by 2032. This reflects the growing trend of adventure travel and overlanding. You can discover more about the growing market for auxiliary fuel tanks if you want to dive into the numbers.
Choosing the Right Tank and Gathering Your Tools
Picking the right auxiliary tank is the most critical decision in this process. You must balance the benefit of added capacity against the penalty of extra weight. A 40-gallon tank sounds incredible, but that’s over 240 pounds of fuel alone.
Where you put the tank is just as important. It will dramatically affect your truck’s handling and cargo space. An in-bed tank is straightforward to install but eats up valuable cargo area.
An under-bed or frame-mounted tank preserves bed space and keeps the center of gravity low. However, the installation will be much more involved. To help you choose, here’s a breakdown of common systems.
Comparing Auxiliary Fuel Tank Systems
| System Type | Best For | Key Advantage | Main Consideration |
|---|---|---|---|
| Gravity-Fed | Simplicity and reliability. A great “set it and forget it” option for tanks mounted higher than the factory one. | Easiest to install with minimal wiring and moving parts. Very dependable. | Fuel transfer is slow and constant. You can’t control when it transfers. |
| Electric Pump | Maximum control and for tanks mounted anywhere, including below the factory tank. | Allows on-demand fuel transfer with a switch. Faster than gravity feed. | More complex installation with wiring and a pump to potentially fail. |
| In-Bed | Quick installations and easy access for filling or maintenance. | Often requires less modification to the vehicle’s frame or underbody. | Consumes significant cargo space in the truck bed. |
| Under-Bed/Frame | Preserving bed space and maintaining a low center of gravity for better handling. | Stays out of the way, leaving your bed completely free for gear. | Installation is much more complex and time-consuming. |
The best system is the one that fits your specific truck and your travel style.
Plumbing and Tool Prep
Once you’ve chosen a location, you need to think about plumbing. A simple gravity-fed system is the most direct route. It usually involves a tee spliced into the factory filler neck hose.
For more control, an electric pump system lets you transfer fuel with a switch. This is essential if your auxiliary tank is mounted lower than your factory one. Our guide on how to pick a fuel transfer tank can help you weigh the pros and cons.
Finally, get every tool ready before you start. Being prepared turns a potential headache into a rewarding weekend project.
Pro Tip: Get a proper set of fuel line disconnect tools and a dedicated hose cutter. Trying to use a knife or regular pliers can damage hoses and cause dangerous leaks. Just get the right tools.
Preparing Your Vehicle for a Safe Installation
Before you grab a wrench, let’s get your rig and workspace ready. Proper prep is non-negotiable for a safe auxiliary tank install. Do not rush this step.
First, disconnect the negative terminal on your vehicle’s battery. This simple move prevents stray sparks or electrical problems.
Work in a well-ventilated space, like an open garage or driveway. You don’t want to breathe in a cloud of fuel vapors. Also, make sure you have a Class B fire extinguisher within arm’s reach.
A successful installation depends on your truck’s condition before you start. Adding over 200 pounds of fuel and steel to a compromised frame is asking for trouble.
Beyond basic fire safety, give your truck a thorough inspection. Get a crawler and slide underneath. Look at the frame rails where you plan to mount the tank.
You’re looking for significant rust, cracks, or any previous damage. This is a big modification, so it’s a good time to check your rig’s overall health. A comprehensive car maintenance checklist can help you spot other potential issues.
It’s far easier to deal with structural problems now than to discover a failure on the trail.
Mounting the Auxiliary Tank Securely
With prep work done, it’s time to mount the tank. Getting the position right is critical for a clean fit and vehicle balance.
Place the empty tank exactly where you plan for it to live. Make sure it’s level and has plenty of clearance from bed walls or other gear. This is a true measure-twice, drill-once situation.
Marking and Drilling Your Mount Points
When you’re happy with the placement, mark your drill points through the tank’s mounting tabs. Use a paint marker or center punch. Then, pull the tank back out so you have a clear shot.
Before you drill, you must look underneath.
CRITICAL SAFETY CHECK: Always verify what is directly behind where you’re about to drill. You do not want to hit a hidden brake line, wiring harness, or exhaust system. That mistake turns a weekend project into a dangerous and expensive mess.
Once clear, start with a small pilot bit. This keeps the larger bit from “walking” and ensures an accurate hole. A little cutting oil will make drilling smoother and save your drill bits.
Securing the Hardware
Use the right hardware for a mounting job that will last. Go for Grade 8 bolts, nuts, and washers. They offer superior strength and vibration resistance.
Finally, tighten everything with a torque wrench to the manufacturer’s specs. This pro touch ensures the tank is locked down securely. It guarantees your new tank can handle years of rough roads.
Plumbing And Wiring Your New Fuel System
This is the part that can seem intimidating: connecting fuel lines and wiring. But if you break it down into smaller tasks, it’s straightforward.
A common way to plumb an auxiliary tank is to splice a tee into the factory filler neck hose. It’s a simple and effective method for gravity-fed systems. Fuel from the new tank flows directly into the main one.
Another route is a dedicated electric transfer pump. This gives you total control via a switch in the cab. Whichever way you go, use a sharp hose cutter and quality fittings with fuel-safe thread sealant.
Routing Hoses And Wires
Properly running your lines is critical for safety and longevity. Secure all fuel hoses far away from hot exhaust, sharp edges, and moving parts. I use cushioned P-clamps to secure hoses to the frame to prevent chafing.
If you use an electric pump, wiring is just as important. Run all wires through a protective loom. The circuit must be properly fused and have a solid, clean ground connection.
A well-built electrical system is as vital as a leak-free fuel line. It’s a core skill, like knowing how to use a winch for a recovery.
It’s interesting to see these same principles in other fields. The aircraft auxiliary fuel tank market, valued at USD 2.1 billion in 2024, is built on the same foundations of secure, reliable fuel transfer to extend operational range. It shows how critical this work is.
Final System Checks and Troubleshooting
You’re in the home stretch. With everything installed, it’s tempting to fill up and go, but this last part is critical. A methodical check now separates a reliable setup from a disaster.
First, don’t fill the whole tank. Just add a gallon or two of fuel. This is enough to pressurize the system and show any potential leaks.
Now, get your eyes on every connection. Trace the lines from the auxiliary tank to the engine. Look for any hint of dampness or the slightest drip.
Common Issues and Quick Fixes
Even a meticulous install can have minor issues. The good news is, they’re usually simple to fix.
- Pump Won’t Turn On: This is usually an electrical problem. Check the fuse, the ground connection, and ensure all plugs are secure. A bad ground is a classic culprit.
- Slow or No Fuel Transfer: If the pump runs but fuel isn’t moving, you may have an airlock or a kinked line. Carefully trace the new hose, making sure there are no sharp bends or pinches.
- Incorrect Gauge Reading: If the gauge is reading funny, check its ground wire first. A poor ground here will throw off the reading every time.
A final system check isn’t just a box to tick. It’s a fundamental part of responsible vehicle modification, much like following a regular truck maintenance checklist. This habit keeps your rig dependable and ready for adventure.
A Few Final Questions
A few questions always pop up before you start turning wrenches. Let’s tackle the common ones.
Should I Hire a Pro for the Install?
This depends on your skill level. If you’re comfortable with fuel systems, wiring, and drilling, you can DIY this project. Many experienced off-roaders do.
However, if any part makes you nervous, it’s smart to call a professional. There’s no shame in it. An expert will get it done safely, which is always the top priority.
What About My Vehicle’s Warranty?
This is a big one. The short answer is: modifying your fuel system might void the warranty on related components.
The best first step is to call your vehicle’s manufacturer or dealership and ask. In the U.S., the Magnuson-Moss Warranty Act offers some protection. It requires a dealer to prove your aftermarket part caused a failure before denying coverage.
Are These Tanks Even Legal Everywhere?
Laws for auxiliary fuel tanks vary by state. Generally, tanks meeting federal Department of Transportation (DOT) standards are fine.
Where things get tricky is the installation method. Some areas have rules against gravity-fed systems. Before you buy a tank, check your local and state regulations.
For more expert guides and off-road gear reviews, check out Offroading.com. We have everything you need to tackle any terrain with confidence. https://www.offroading.com
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