Designed for 2-Inch OD Fuel Tank Filler Necks
The Moroso 65385 is designed around a 2-inch outside-diameter fuel filler tube.
Installation involves removing approximately a 3-inch section of the appropriate filler-neck area and installing the aluminum adapter between the remaining sections using the supplied flexible sleeves and clamps. Moroso’s current product description specifies removing approximately 2-3/4 inches when fitting the adapter.
Before purchasing, measure the actual filler-neck diameter on the vehicle.
This is not a direct-fit kit for every make and model simply because the vehicle has a fuel tank and hopes for the best.
3/8-Inch Aluminum Fuel Return Fitting
The adapter incorporates a 3/8-inch aluminum fuel fitting.
This fitting provides the connection point for the return line running from the EFI regulator’s bypass/return port toward the tank.
Moroso recommends its 65330 3/8-inch OD aluminum fuel line for plumbing between the EFI regulator and the filler-neck return fitting.
The appropriate return-line size should always be confirmed against the requirements of the regulator, fuel pump, EFI system, and engine combination.
Factory-Welded Return Fitting
The 3/8-inch aluminum fitting is factory welded to the adapter, eliminating the need for the installer to fabricate or weld the return connection onto the adapter.
This provides a permanent metal connection between the return fitting and the filler-neck adapter.
For custom EFI installations, that means one less critical fuel-system joint that needs to be fabricated in the garage.
Internal 90-Degree Return Tube
The return fitting doesn’t simply dump fuel randomly into the filler neck.
Inside the Moroso adapter is a smooth-contour 90-degree bend designed to direct the returning fuel downward toward the tank.
Correct adapter orientation is critical.
Moroso specifically warns that the inner return tube must point toward the fuel tank. Installing it backward could direct returning fuel toward the filler-cap opening instead.
That’s a mistake worth avoiding for reasons that hopefully don’t require a demonstration.
Two Buna-N Filler Neck Sleeves
The kit includes two Buna-N sleeves that connect the aluminum adapter to the existing filler tube.
Buna-N, also known as nitrile rubber, is commonly used for petroleum-fuel sealing applications.
One sleeve is installed at each side of the adapter, creating flexible connections between the original filler neck and the new aluminum return section.
Four Stainless-Steel Hose Clamps
Four stainless-steel hose clamps are included to secure the two Buna-N sleeves.
Using two clamps at each adapter connection creates a mechanically secure filler-neck assembly when properly installed.
After installation, every connection should be inspected carefully for leakage before the engine is started.
Ideal for EFI Conversion Projects
The Moroso 65385 is particularly useful when converting an older vehicle to modern electronic fuel injection.
Potential applications include:
- Aftermarket throttle-body EFI
- Multi-port EFI conversions
- LS engine swaps
- Restomod fuel systems
- Classic muscle cars
- Street rods
- Hot rods
- Custom EFI conversions
- Return-style fuel-pressure regulator installations
- Electric fuel-pump conversions
Fitment ultimately depends on the fuel filler-neck dimensions and available installation space, not simply the engine installed in the vehicle.
Useful for LS Swap Fuel Systems
An LS swap often requires significant changes to an older vehicle’s fuel system.
Many factory LS EFI combinations require high-pressure electric fuel delivery and a properly configured pressure-control system.
Depending on the regulator and fuel-rail arrangement, that can mean adding a return circuit to a chassis that never had one.
The Moroso 65385 provides one way to add that return connection without welding a fitting directly into the fuel tank.
If you’re planning the rest of the conversion, the Pro Street Ultimate GM LS Engine Guide covers the LS family and the considerations involved when installing one into another chassis.
For an application-specific example, Pro Street’s LS1 240SX Swap Guide also discusses the fuel-pressure requirements involved when installing an LS1 into a chassis originally designed around a completely different engine.
How a Return-Style EFI Fuel System Works
A return-style EFI system generally uses a bypass regulator to control fuel pressure by routing fuel that the engine doesn’t currently require back toward the tank.
A simplified layout might look like:
Fuel Tank → EFI Fuel Pump → Filter → Fuel Rail → Fuel Pressure Regulator → Return Line → Moroso 65385 → Fuel Tank
Actual component placement varies according to the EFI system.
The return circuit matters because the regulator must be able to bypass enough fuel to maintain the required pressure.
An undersized or restricted return line can make pressure difficult to control.
For a deeper explanation, the Pro Street Fuel Pressure Regulator Guide covers bypass regulators, fuel pressure, return circuits, and performance fuel-system design.
Return-Style vs. Returnless EFI
Not every EFI conversion requires a full-length return line from the engine compartment.
Some systems use an in-tank or rear-mounted regulator arrangement that returns fuel close to the tank. Others use a conventional bypass regulator near the engine, requiring a return line from the regulator back toward the tank.
The Moroso 65385 is particularly useful for systems that need a dedicated external return connection at the tank.
Before purchasing, determine exactly how the chosen pump, regulator, rail, and EFI system are intended to be plumbed.
Moroso 65385 Installation Overview
Moroso provides detailed installation instructions for the 65385, and those instructions should be followed completely.
At a high level, installation involves:
- Locate and measure the fuel tank filler neck.
- Confirm a suitable 2-inch OD installation section.
- Drain the fuel system as required.
- Safely access or remove the fuel tank where necessary.
- Remove the specified section of filler tubing.
- Remove all cutting debris.
- Install the supplied sleeves over the filler-neck sections.
- Insert the Moroso aluminum adapter.
- Orient the internal return tube toward the tank.
- Secure the assembly with the four supplied clamps.
- Fabricate the 3/8-inch return connection from the EFI regulator.
- Reassemble the fuel system.
- Add fuel and inspect every connection for leakage.
- Start the engine only after confirming that the system is leak-free.
- Inspect the system again while the engine is running.
Moroso notes that some installations can be performed without removing the fuel tank, while others require tank removal depending on filler-neck construction and vehicle configuration.
Fuel Tank Safety Is Critical
Fuel-system modification requires special care because gasoline vapor is extremely flammable.
Moroso’s instructions specifically warn installers to follow proper gasoline safety procedures and recommend keeping a fire extinguisher ready during installation.
Never cut, drill, grind, or weld around a fuel tank that has not been made safe using the proper procedure.
If the installation requires tank removal or filler-neck modification beyond your experience level, have the work performed by a qualified professional.
Why Choose the Moroso 65385 EFI Return Line Kit?
The Moroso 65385 solves a very specific problem extremely well: adding a dedicated EFI return connection to an older fuel system without welding directly onto the tank.
Key features include:
- Designed for EFI conversion return systems
- Installs into compatible 2-inch OD filler necks
- 6061-T6 aluminum adapter
- Factory-welded 3/8-inch aluminum return fitting
- Internal 90-degree return tube
- Directs return fuel toward the tank
- Two Buna-N connecting sleeves
- Four stainless-steel clamps
- Can install on many vehicles without tank removal
- Compatible with custom return-style EFI plumbing
- Made in the USA
For classic cars and engine swaps where the original tank doesn’t provide a convenient EFI return, the Moroso 65385 offers a clean alternative to fabricating a return fitting directly into the tank.
Frequently Asked Questions
What is the Moroso 65385?
The Moroso 65385 is an EFI fuel return line adapter kit designed to add a return connection to a compatible fuel tank filler neck.
What size filler neck does Moroso 65385 fit?
The kit is designed around a 2-inch outside-diameter fuel tank filler tube.
What size is the return fitting?
The adapter has a 3/8-inch aluminum fuel return fitting.
Do I have to weld the Moroso 65385 to the tank?
No. Avoiding the need to weld a return fitting onto the fuel tank is one of the main purposes of the kit.
Is the 3/8-inch fitting welded to the adapter?
Yes. The aluminum return fitting is factory welded to the adapter.
What are the flexible sleeves made from?
The kit includes two Buna-N sleeves.
How many clamps are included?
Four stainless-steel hose clamps are supplied.
Which direction should the internal return tube face?
It must face toward the fuel tank. Moroso warns against installing the internal tube toward the filler opening.
Does the fuel tank have to be removed?
Not always. Moroso states that the adapter can install on many vehicles without tank removal, but some filler-neck configurations require the tank to be removed.
What return line does Moroso recommend?
Moroso recommends its 65330 3/8-inch OD aluminum fuel line for connecting the EFI regulator return to the filler-neck adapter.
Is the Moroso 65385 vehicle specific?
No. Although some catalog data describes fitment generically, Moroso’s installation design is based primarily around a compatible 2-inch OD filler neck and sufficient installation space rather than one specific vehicle model.
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