Harley Davidson Plumb In A 2nd Fuel Tank: Ultimate Guide for Longer Rides

Why Riders Choose to Harley Davidson Plumb In A 2nd Fuel Tank

Planning a cross-country tour on your Harley? Running out of fuel in the middle of nowhere isn’t just inconvenient—it’s dangerous. Many Harley Davidson owners solve this by choosing to Harley Davidson plumb in a 2nd fuel tank, effectively doubling their range without sacrificing style or performance. Whether you’re a weekend warrior or a serious road tripper, this mod can transform your riding experience. And no—you don’t need to be a mechanic genius to pull it off.

What Does “Plumb In A 2nd Fuel Tank” Actually Mean?

“Plumbing in” a second fuel tank means connecting an auxiliary tank to your bike’s existing fuel system so it feeds gasoline into the engine seamlessly. Unlike external jerry cans (which are bulky and unsafe), a properly plumbed second tank integrates with your bike’s fuel lines, petcock, and sometimes even the fuel injection system.

According to the American Motorcyclist Association (AMA), over 22% of long-distance touring riders use auxiliary fuel solutions—many of them professionally installed or DIY dual-tank setups.

Is It Legal and Safe to Add a Second Fuel Tank to Your Harley?

Yes—but with caveats. The U.S. Department of Transportation (DOT) doesn’t prohibit auxiliary fuel tanks, but local state laws may impose restrictions on tank placement, material, and venting. For example:

• California requires EPA-compliant evaporative emissions controls.
• Texas allows auxiliary tanks as long as they’re securely mounted and don’t obstruct controls.

Safety-wise, the biggest risks are fuel leaks, vapor buildup, and fire hazards—all avoidable with proper materials and installation. Always use DOT-approved fuel lines, marine-grade fittings, and vented caps. Never use PVC or non-ethanol-resistant tubing.

💡 Pro Tip: The Motorcycle Safety Foundation (MSF) recommends pressure-testing your plumbing at 3–5 PSI before your first ride.

Step-by-Step: How to Harley Davidson Plumb In A 2nd Fuel Tank

Here’s a simplified, beginner-friendly guide. Always disconnect your battery before starting.

Tools & Materials Needed:

• 6–8 ft of ethanol-resistant fuel line (SAE J30 R9 or R14 rated)
• Inline fuel shut-off valve (manual or electric)
• T-fitting (brass or stainless steel)
• Auxiliary fuel tank (3–5 gallon capacity; aluminum or rotational-molded plastic)
• Hose clamps, zip ties, wrench set
• Fuel stabilizer (for long-term storage)

Step 1: Choose Your Auxiliary Tank Location

Common spots:

• Behind the rear fender (touring models)
• Under the seat (softails—limited space)
• Saddlebag replacement (custom builds)

Ensure at least 2 inches of clearance from exhaust pipes and moving parts.

Step 2: Mount the Tank Securely

Use stainless steel brackets. The tank must withstand 8G of force (FMVSS Standard 301). Test by shaking vigorously—no movement should occur.

Step 3: Install the T-Fitting

• Locate the main fuel line between your stock tank and fuel pump/injector.
• Cut the line and insert a brass T-fitting.
• Connect one arm to your stock tank, the other to the auxiliary tank.

Step 4: Add a Shut-Off Valve

Install an inline valve on the auxiliary line. This lets you:

• Isolate the second tank when empty
• Prevent siphoning
• Switch between tanks manually

⚠️ Never run both tanks open simultaneously unless using a balance system—this can cause uneven fuel draw or flooding.

Step 5: Vent the Auxiliary Tank

All fuel tanks must be vented to prevent vacuum lock. Use a filtered vent line routed away from hot surfaces. Reference EPA fuel system guidelines.

Step 6: Pressure & Leak Test

• Fill both tanks with 2 gallons of fuel.
• Start the engine and check for leaks at all connections.
• Ride slowly for 10 minutes, then re-inspect.

Pros and Cons of Adding a Second Fuel Tank to Your Harley

Real Rider Case Study: Cross-Country with Dual Tanks

Mike R., a retired firefighter from Colorado, installed a 5-gallon auxiliary tank on his 2019 Road Glide.

“I rode from Denver to Key West—1,800 miles—without a single fuel anxiety moment. My stock tank gives me 130 miles; the second added another 160. Total cost: $320 in parts and a weekend of work.”

His setup used a Marine-grade aluminum tank from AeroFuel and an electric solenoid valve controlled by a dashboard switch.

Common Mistakes to Avoid

1. Using non-ethanol-resistant hoses → Degrades in 30 days with E10 fuel.
2. Ignoring tank venting → Causes engine sputter or starvation.
3. Mounting near exhaust → Fire risk! Maintain 6+ inches clearance.
4. Skipping the shut-off valve → Risk of uncontrolled siphoning.

For more on fuel system safety standards, see the U.S. DOT’s motorcycle guidelines on Wikipedia.

FAQ: Harley Davidson Plumb In A 2nd Fuel Tank

Q1: Will adding a second fuel tank void my Harley warranty?
A: Possibly. If the dealer determines a failure (e.g., fuel pump) was caused by your modification, they may deny coverage under the Magnuson-Moss Warranty Act. However, unrelated components (like brakes) remain covered. Always document your install.

Q2: Can I use the second tank as my primary fuel source?
A: Yes—but ensure it’s gravity-fed or pump-assisted if mounted lower than the carburetor/injector. Most auxiliary tanks are designed as reserve, not primary.

Q3: How much range will I really gain?
A: A typical Harley gets 40–45 MPG. A 4-gallon auxiliary tank adds 160–180 miles. Real-world range depends on riding style, terrain, and load.

Q4: Do I need to rejet my carburetor or remap my EFI?
A: No. As long as fuel pressure and delivery remain consistent (via proper plumbing), your engine management system won’t be affected.

Q5: What’s the cheapest way to do this?
A: DIY with a used Rotopax 4-gallon tank ($120), ethanol-safe hose ($25), and a manual valve ($30). Total under $200.

Q6: Can I install this on a fuel-injected Harley?
A: Absolutely. Fuel-injected models (post-2008) actually simplify plumbing—just tap into the return line or pre-pump feed. Avoid modifying the high-pressure side.

Final Thoughts: Is It Worth It?

If you love long rides, remote trails, or just hate gas station detours, learning how to Harley Davidson plumb in a 2nd fuel tank is a game-changer. It’s a practical, cost-effective upgrade that boosts both confidence and convenience. Just follow safety protocols, use quality parts, and test thoroughly.

🏍️ Ready to extend your horizon? Share this guide with a fellow rider on Facebook or Reddit—and tag us on Instagram with your dual-tank build! #HarleyDualTank #LongHaulRider

Remember: Great rides aren’t measured in miles—but in how far you dare to go without looking back.