Sylvie Willis
Connecting a 3/8 hard fuel line to an engine can be a tricky process. It involves a range of considerations, from the type of fittings and tubing to the placement of the fuel line itself. The tubing must be bent to fit the engine, and the right fittings must be chosen to ensure a secure connection. This process can be complex, with many potential pitfalls, and it's important to choose the right tools and materials to avoid issues down the line.
Characteristics and their values for connecting 3/8" hard fuel lines:
| Characteristics | Values |
|---|---|
| Fuel line material | Steel, stainless steel, rubber, nylon |
| Fittings | Flare, flare union, compression union, tube nuts, AN(JIC) union, Dorman nylon line, GM style fittings |
| Tools | Swedging tool, MAP gas torch, Oaty flux, Oaty solder, acetylene torch, brazing rod, flaring tool |
| Hose clamps | Hose clamps can be used to secure the fuel line |
| Brackets | Used to hold the fuel line in place, may need to be purchased separately |
| Fuel pump | A high-flow mechanical fuel pump may be required |
| Hose fittings | Push-on rubber hose fittings can be used |
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What You'll Learn
Using a flare union
Fittings are available to connect two 3/16" hard fuel lines. A double flare union is one way to do it. This method is not recommended for high-pressure applications. You can get two tube nuts and an AN(JIC) union from your local hydraulic shop.
One user recommends using Dorman nylon lines and GM-style fittings. You will need a 3/8" supply and 5/16" return. You must have the Dorman tool to insert the line over the GM fittings, although there are alternative methods of doing this without the tool.
Another user recommends using 3/8" and 5/16" brake lines with F.I. rubber hose for flex at the engine and filter. You can obtain GM fuel line fittings from your local junkyard at reasonable prices. Dorman nylon line is available at O'Reilly's in 25-foot rolls.
You can also join the two lines with a positive seal by double flaring them (inverted flare) like you would join two brake lines with a union between them. This method is rated for over 1200 psi and can be done with minimal tooling. You can buy a 7-piece tube flaring kit from Harbor Freight and pick up two nuts and the union at most auto parts stores.
Another user recommends using a swedging tool and putting one line inside the other, then sweating it like a copper water pipe. You will need a MAP gas torch, Oaty flux, Oaty Solder, and a swedging tool. You can get the MAP torch and Oaty flux at Home Depot, and the swedging tool at Harbor Freight or an HVAC supply store.
You could also use a flare union if the lines ever need to come apart. Compression unions are not recommended by this user, but they can be picked up at any hardware store. Note that compression fittings are not legal for fuel and brake lines in Canada and would not pass safety.
Another user recommends using 5/16" and 1/4" compression fittings to create some homemade "barbs" on the steel lines. Install a compression fitting conventionally, then remove the coupling. Next, swedge the ferrule onto the steel line, then cut the compression nut off the hard line with a Dremel and cut-off wheel. Now, push the EFI-rated hose well past the ferrule. With the clamp in place and tight, it becomes nearly impossible for the hose to move over the larger diameter created by the ferrule swedged onto the hard line.
One user is re-routing the stock fuel line (and return line) on their '69 BB to provide header clearance. They cut the original 3/8 line at the frame rail and used 3/8 aluminum tubing to form the new piece. They bent it by hand without kinking it, then did the "start" of a 45-degree flare to expand the tubing a little, then slid a short section of braided line over both pieces where they join and hose clamped them. They plan to one day double flare both pieces and use a flare union.
Earls Auto-Fit fittings (3/8" fuel line and 1/4" return line) are also recommended by a user and are easy to attach with no leaks. They also used Earls Pro-lite braided nylon hose along the top of the frame rails to the FP.
Inline Tube Replacement For 5/8-18 Inverted Flare Union is available on Amazon for 3/8" fuel lines. Unions are used to join two brake, fuel, or transmission lines together. It is important that both flare type and thread match for a leak-proof connection.
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Using compression unions
Compression unions are a cheap, easy, and readily available method of connecting hard fuel lines. They are suitable for high-pressure applications, with some products capable of withstanding up to 5,000 PSI. They are also protected against rust and corrosion.
To use a compression union, start by cutting your line and installing fittings/ferules. Then, tighten the connection. This method is cleaner than splicing in some stainless braided. You can also use a flare union if you need to separate the connection later.
Some users have expressed concerns about the safety of compression unions, noting that they are not legal for fuel and brake lines in Canada. However, others have used them successfully on fuel lines without issues.
You can purchase compression unions and fittings from various online retailers and hardware stores. Some retailers offer kits that include all the necessary components for creating replacement fuel lines, such as connectors, compression unions, adapters, and nylon fuel lines. These kits can save time and money by providing all the necessary tools in one package.
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Using a swedging tool
To connect two 3/16" hard fuel lines, you can use a swedging tool. This method involves putting one pipe inside the other and sweating them together, similar to how copper water pipes are joined. Here is a step-by-step guide on using a swedging tool for this purpose:
- Prepare the Pipes: Ensure you have the correct pipe dimensions for your project. In this case, you are working with 3/16" hard fuel lines.
- Obtain a Swedging Tool: Purchase or rent a swedging tool. You can find these at hardware stores, specifically at Harbor Freight or an HVAC supply store.
- Insert and Sweat the Pipes: Using the swedging tool, insert one pipe inside the other. Then, apply heat to sweat the joint, similar to soldering copper pipes.
- Materials and Safety: For safety, use a MAP gas torch along with Oaty flux and Oaty Solder. The user in the forum recommends Oaty brand due to their positive experience. These materials can be found at Home Depot.
- Brazing: If you want an even stronger joint, you can use an acetylene torch to braze the joint with a brazing rod. This provides a secure connection.
- Alternative Methods: While swedging is a recommended method, you can also consider flare unions or compression unions as alternative connection methods. However, some users in the forum expressed concerns about the aesthetics and safety of compression unions.
- Nylon Lines: If you are working with fuel injection lines, consider using Dorman nylon lines with GM-style fittings. The nylon lines are resistant to fuel additives that can degrade regular rubber hoses.
- Double Flaring: For a positive seal, you can double flare the lines (inverted flare) using a flaring tool. This method creates a secure joint similar to how brake lines are joined.
- Adapters: Depending on your specific application, you may need adapters to connect different types of fittings. For example, when connecting a fuel line to a mechanical fuel pump, you may need an adapter to transition from a 3/8" line to a smaller fitting.
Remember to prioritize safety and follow local regulations when working with fuel lines. Always consult a professional if you have any doubts about the procedure or the materials being used.
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Using a flaring tool
There are a few different types of flares that can be used, including a double flare, an inverted flare, and a bubble flare. The type of flare you choose will depend on the specific application and the tools you have available. For example, a double flare is easy to do yourself with minimal tooling, whereas a bubble flare can be replicated using a bubble flare tool.
To create a double flare, you can use a 7-piece tube flaring kit, which can be purchased from auto parts stores or Harbor Freight. This type of flare is not recommended for high-pressure applications. First, place the inverted flare fitting (45-degree flare) or tube nut and tube sleeve (37-degree flare) over the cut and finished end of your line. This will prevent you from forgetting to add the fitting later. Then, use the flaring tool to create the flare.
For a bubble flare, you can use a bubble flare tool to replicate a bead-rolled end, and then push a soft fuel hose over the flared end, securing it with a fuel hose clamp. This method is safe for stock fuel systems with pressure around 50 psi, but it is not recommended for higher pressures.
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Using a braided stainless steel hose
Braided stainless steel hoses are a popular choice for fuel lines, especially in high-performance applications. They offer the highest level of performance and are designed to handle the demands of high-performance racing cars. They are also suitable for daily drivers who want the highest-performing fuel lines.
When using a braided stainless steel hose to connect a 3/8 hard fuel line, there are a few things to keep in mind. First, you need to ensure that you have the correct hose size. The hose diameter and length must be appropriate for your vehicle's fluid system. Too small a diameter may restrict the flow rate, while too large a diameter may result in inadequate pressure. The length of the hose should also be considered, as it will affect the system's flow rate and pressure.
To connect the braided stainless steel hose to the 3/8 hard fuel line, you will need the appropriate fittings. Fittings are available in various materials, including brass, steel, and nylon. You can source these fittings from automotive stores or hydraulic shops. The fittings will ensure a secure connection between the braided hose and the hard fuel line, preventing leaks and ensuring optimal performance.
When installing the braided hose, it is essential to consider its routing and any necessary bends. Braided stainless steel can be more challenging to work with than other materials, so a strong tubing bender is recommended. Additionally, if you need to cut the braided hose, it is advised to use a hacksaw instead of a tubing cutter, as the latter can work-harden the stainless steel, making it harder to flare.
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Frequently asked questions
You can flare the end of the line and adapt the metal line from a 3/8" flare fitting to the rubber hose fitting.
Retroford offers a 3/8" Push-On Fittings Hard Fuel Line Kit with R9 rubber hose and grey brackets. AGS Company also offers a master kit that contains all the connectors, compression unions, adapters, and nylon fuel line needed to make quick and cost-effective replacement lines.
Avoid using soft lines as fuel additives can damage them over time. Braided stainless steel AN-6 hoses are a good option as they will not rot.
You will need a swedging tool, a MAP gas torch, Oaty flux, and a swedging tool.
It is important to consider the bends and test fit to ensure a proper connection. Pre-bent lines can save time and money. If you are using a mechanical fuel pump, you may need to adapt the line to the pump inlet.
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