Pressurizing Fuel Tanks: Detecting Leaks With Pressure Testing

Fuel tank pressure testing is a crucial aspect of vehicle maintenance, helping to ensure safety, efficiency, and performance. This process involves pressurising the tank with air and monitoring for leaks or pressure loss, which could indicate a range of issues, from increased fuel consumption to fire hazards.

There are several methods for testing fuel tanks for leaks, ranging from DIY approaches to those requiring specialised equipment and qualified mechanics.

One common method is to use compressed air and a pressure gauge to pressurise the tank and monitor for pressure drops. This can be done by sealing the tank's openings, introducing compressed air, and using a pressure gauge to monitor for changes. A soapy water solution is then applied to the tank and its components to check for leaks.

Another approach is to use a cylinder leak-down tester, which involves connecting the tester to the tank's petcock and an air compressor. By regulating the airflow and observing the pressure, you can identify potential leaks.

For those seeking a DIY solution, a simple bike pump can be used to pressurise the fuel system and listen for leaks. This method may not detect slower leaks but can be a quick and accessible way to identify serious issues.

It is important to note that fuel tank pressure testing should be conducted with caution, as too much pressure can deform or damage the tank. It is recommended to consult a qualified mechanic or perform the test under expert guidance.

Prepare the tank

Before performing a fuel tank pressure test, it is important to prepare the tank properly to ensure accurate results. Here are the steps you need to follow:

• Drain the tank: If the fuel tank is still attached to the vehicle, make sure to drain it completely. This will ensure that you are working with an empty tank, which is essential for safety reasons and to get accurate test results.
• Remove the fuel tank: Carefully remove the fuel tank from the vehicle, if possible. This will make it easier to access all the necessary openings and connections during the test.
• Clean the tank: Once the tank is empty, clean it thoroughly to remove any fuel residue or debris. This step is crucial to ensure that residual fuel does not affect the test results or pose a safety hazard.
• Inspect the tank: After cleaning, carefully inspect the tank for any visible signs of damage, such as dents, scratches, or corrosion. Pay close attention to the welds, seams, and fittings, as these are common areas for leaks.
• Seal the openings: Identify all the openings in the fuel tank, such as the filler neck, vent, and outlet. Seal off these openings securely to ensure that the tank can be pressurised. You can use various methods for sealing, such as tape, plugs, or custom-made fittings.
• Connect the pressure gauge: Attach a pressure gauge to one of the sealed openings. This gauge will allow you to monitor the pressure level inside the tank during the test. Ensure that the gauge is functioning properly and that you can easily read the measurements.
• Prepare the compressed air source: You will need a source of compressed air to pressurise the tank. This can be an air compressor or a compressed air tank. Ensure that the air source is capable of providing the required pressure and that all hoses and connections are secure.
• Park the vehicle: If you are unable to remove the fuel tank, park the vehicle on a level surface and engage the parking brake. Ensure that the engine is turned off and has had sufficient time to cool down.
• Locate and inspect the fuel tank pressure sensor: If your vehicle has a fuel tank pressure sensor, locate it and inspect it for any signs of damage or corrosion. Ensure that the sensor and its wiring harness are securely connected and free from debris.
• Gather necessary tools: In addition to the pressure gauge and compressed air source, gather any other tools or equipment you may need during the test. This may include soap and water for leak detection, a multimeter for electrical measurements, and a diagnostic scanner for accessing sensor data.

Once you have completed these steps, you will be ready to begin the fuel tank pressure test. Remember to work carefully and follow all safety precautions when working with pressurised systems.

Pressurise the tank

The first step in pressurising the tank is to ensure that it is safe to do so. If the tank has held gasoline, it is important to purge it of any gasoline fumes. Use a funnel in the gas tank's filler hole and place the larger end of the funnel into the exhaust pipe of your car. Make sure any petcocks are open, and then let the car run for 30 minutes. This will allow the gasoline fumes to escape.

After this, it is important to check for any residual fumes. Using a torch, light it and stick it down the filler hole. If there are any residual fumes, a small flame will shoot out.

Now, the tank is ready for the leak down test. You will need a cylinder leak down tester, which can be purchased from an auto parts store. You will also need some extra hose and fittings to create an adapter kit, allowing you to connect the tester to the tank.

Connect the hose to the petcock and keep it open. If there is a second petcock, close it to maintain pressure in the tank. Connect the other side of the hose to the leak down tester and the tester to an air compressor. It is important to regulate the air pressure so that it is not too high. You should be able to hold your hand over the filler hole with some pressure but without too much force. You can also put your finger over the vent hole of the gas cap to build pressure.

Once the tank is pressurised, it is time to check for leaks. A common area for leaks is the gas cap, so if you are using a vented cap, cover the vent hole with your finger and spray soapy water towards the cap. If the pressure is correct, you should see bubbles.

Next, spray soapy water all over the tank, inspecting weld seams, fittings, and mounts for any leaks. If you find a leak, you will see bubbles forming and growing in that area. Mark the location of the leak and continue searching for more.

Prepare the area for repair

Once you have identified the location of the leak, it is time to prepare the area for repair. Use an air grinder with a wire brush or steel wool to clean the area. Remove any paint from the area, but be careful not to remove any metal. It is good practice to clean a larger area, as the crack may be larger than it appears.

Repair the leak

Now it is time to weld up the leak. Use a TIG or MIG welder with filler to repair the pinhole or crack. Do not braze it!

Re-test the tank

After repairing the leak, it is important to re-test the tank to ensure that the repair was successful. Re-pressurise the tank and inspect the repaired area for any signs of leaks. If the leak is gone, you are ready for the next step in your project.

Monitor pressure levels

Monitoring pressure levels is a crucial aspect of testing a fuel tank for leaks. It involves introducing compressed air into the sealed tank to reach a specific pressure and then observing the pressure behaviour over time.

The pressure level in the tank is typically monitored using a pressure gauge. This gauge allows you to track the pressure and identify any sudden drops, which could indicate a leak. It is important to be cautious and not exceed the safe pressure limit for the tank, as too much pressure can deform or even destroy the tank.

The pressure test should be conducted over a sufficient period to ensure accurate results. While some sources suggest that holding the pressure for a few days is ideal, others recommend a minimum of 15 minutes to account for temperature fluctuations that can affect pressure readings.

During the pressure test, it is crucial to closely observe the pressure gauge and watch for any pressure drops. A decrease in pressure could indicate a potential leak, and further investigation would be necessary.

If the pressure remains stable within the specified range, it suggests that the tank is intact and not leaking. However, if the pressure drops or leaks are detected, further inspection and repairs will be required.

Inspect for leaks

Inspecting for leaks is a crucial aspect of fuel tank pressure testing. Here is a detailed guide on how to inspect for leaks during the testing process:

Preparation:

• Ensure the vehicle is parked on a level surface, and the fuel tank is not overfilled.
• Inform the mechanic about any issues with fuel efficiency or engine performance.
• Address any diagnostic trouble codes related to the fuel system beforehand for accurate test results.

Testing Procedure:

• Seal off all openings of the fuel tank.
• Introduce compressed air into the tank to reach a specific pressure. Avoid over-pressurizing the tank, as it can cause deformation or even rupture.
• Monitor the pressure level over time using a pressure gauge. Any pressure drop suggests a potential leak.
• Inspect the tank and its components for leaks. A soapy water solution or a liquid dye can be used to identify leaks more easily. Spray the solution or apply the dye on the tank's seams, fittings, and welds, which are common leak areas. Look for bubbles or dye penetration, indicating the presence of a leak.
• If a leak is detected, determine its exact location and perform the necessary repairs. Welding or patching may be required, depending on the severity of the leak.
• Re-test the tank after repairs to ensure the leak has been successfully addressed.

Safety Considerations:

• Fuel tank pressure testing should be performed by qualified mechanics or at reputable auto repair shops due to specialized tools and safety considerations.
• Always wear appropriate safety gear, such as face protection, when testing for leaks, especially if using an open flame to check for residual fuel fumes.

Repair leaks and re-test

Once you've identified a leak in your fuel tank, the next step is to repair it. The specific repair method will depend on the type of tank and the nature of the leak. Here are some general guidelines for repairing leaks and re-testing your fuel tank:

• Assess the damage: Not all leaks can be repaired. If your fuel tank has major damage, such as gashes from road debris, large holes, or extensive corrosion, it is best to replace the entire tank. Minor leaks, such as pinhole leaks or small rust spots, can be temporarily repaired using epoxy or other sealants.
• Prepare the work area: Fuel leaks can be dangerous, so it is important to work in a well-ventilated area. Extinguish any open flames or pilot lights, as gas fumes can travel and cause an explosion.
• Clean and prepare the tank: Use sandpaper to clean and roughen the area around the leak. This will remove any paint, rust, or grime and provide a better surface for the repair material to adhere to. Be careful not to use power tools, as sparks could ignite gas fumes. Also, clean the tank with a brake cleaner or carb cleaner to remove any residual fuel or oil.
• Apply the repair material: There are several products available for repairing fuel tank leaks, such as epoxy putties (e.g., JB Weld Autoweld or SteelStik), sealants (e.g., PR-1422 CLASS B FUEL TANK SEALANT SEMKIT - B2), or even a stainless metal screw for small holes. Follow the instructions for your chosen product, ensuring that you mix and apply the material properly.
• Allow the repair to cure: Most repair materials will need time to harden and fully cure. Refer to the product instructions for the recommended curing time.
• Re-test for leaks: Once the repair is cured, re-test the fuel tank for leaks. You can use the same methods described above, such as pressurizing the tank with air and spraying the seams with soapy water, to check for any remaining leaks. If the repair was successful, you should no longer see any bubbles or pressure drops indicating a leak.

Remember, these are general guidelines, and the specific repair process may vary depending on your fuel tank and the type of leak. Always prioritize safety and follow the instructions for any products you use. If you are unsure or uncomfortable with performing the repair yourself, it is best to consult a professional or take your vehicle to a repair facility.

Frequently asked questions