65 Mustang AN fuel line leaking diagnosis
This video diagnoses and repairs a leaking AN-style fuel line on a 1965 Ford Mustang. It shows how to locate the leak, determine whether the hose or AN fittings are at fault, and how to properly replace or reassemble the fuel line and test for leaks.
Build Sequence
1. Safety first: Prepare the vehicle
Park on level ground, chock wheels, disconnect the battery to prevent sparks, and raise the car with a jack and secure on jack stands if needed to access the fuel line.
2. Relieve fuel system pressure
Relieve fuel system pressure before loosening fittings by using the fuel pressure relief method for your setup or removing the pump fuse and running the engine until it stalls. Have a catch pan and rags ready.
3. Visual inspection to locate leak
Inspect the AN fittings and hose along the fuel line for wet spots, cracks, fraying, loose fittings, or fuel spray patterns. Clean the area with rags to reveal the exact leak source.
4. Tighten fittings and re-check
If the leak appears to be from a loose swivel fitting, use the appropriate AN/open-end wrench to snug the fitting (do not overtighten). Clean and re-inspect for leaks under pressure.
5. Assess hose and fitting condition
If tightening doesn't stop the leak, check for damaged hose, corroded or cracked fitting surfaces, or improper assembly of hose ends. Decide whether to replace hose, fittings, or both.
6. Remove and replace damaged components
Loosen and remove the leaking section: catch fuel, remove old hose or fittings, and install replacement braided AN hose or rubber hose and new AN fittings as required. Ensure correct AN size and orientation.
7. Proper assembly and torque
Assemble AN swivel fittings correctly (hand-start threads, then wrench-torque to proper feel) and for rubber hose use proper clamps. Avoid PTFE tape on AN sealing surfaces; verify threads seat properly.
8. Pressure test for leaks
Reinstall any removed components, reconnect the battery or fuel pump fuse, pressurize the fuel system (or use a fuel pressure gauge) and inspect all connections for leaks while the system is pressurized.
9. Final inspection and cleanup
Lower the car if raised, ensure no fuel smell, tighten any remaining clamps, dispose of contaminated rags properly, and perform a short road test while monitoring for leaks.
Frequently Asked Questions
How can I safely check for leaks after repair?
After reassembly, pressurize the fuel system and inspect connections visually for drips or spray. Use a fuel pressure gauge to confirm pressure holds steady. Do the check with a catch pan and rags ready, and perform a brief road test while monitoring.
VIEW FULL ARTICLE →What commonly causes an AN fuel line to leak?
Leaks typically come from loose swivel fittings, damaged or frayed hose, improperly assembled hose ends, or corroded/damaged mating surfaces on AN fittings. Over-tightening or using thread sealant on AN swivel seats can also cause leaks.
VIEW FULL ARTICLE →What size AN fitting do I need for my 1965 Mustang?
AN size depends on your fuel system setup (carburetor feed, fuel pump, return system). Common sizes are -6 or -8 AN for small-block V8s, but verify the hose and fitting size used on your specific installation before ordering replacements.
VIEW FULL ARTICLE →Can I reuse my AN fittings or should I replace them?
You can reuse AN fittings if the sealing surfaces and threads are undamaged and the hose ends were properly assembled. Replace fittings that are rounded, cracked, corroded, or show damaged sealing surfaces.
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Parts Used (5)
Use SAE-approved clamps if replacing rubber hose sections; not required for proper AN swivel hose ends.
PTFE/braided fuel-safe hose recommended for AN fittings; pick correct AN size (-6, -8, etc.) for application.
Replace damaged or corroded AN fittings; ensure correct male/female sizes and thread orientation for your setup.
Used if braided AN hose is not being installed right away or for short replacement runs; ensure fuel-rated material.
Helpful to check for pressure drops and confirm leaks while under fuel pressure.