How to Check a Generator Fuel System for Leaks

Why fuel leaks matter

A fuel leak on a generator is not just a mess. Fuel that drips onto a hot engine or exhaust can ignite, and gasoline vapors spread quickly. Because generators burn fuel, any leak in the fuel system also raises the risk of a fire in a location where you may already be dealing with an emergency power outage. Checking the fuel system is a routine inspection that belongs on your generator safety checklist.

Leaks also tie into carbon monoxide safety. A damaged fuel line can allow the engine to run unevenly, which may change how the generator burns fuel and how much carbon monoxide it produces. The CPSC warns that one portable generator produces as much CO as hundreds of cars and that CO can kill you in minutes. Keeping the fuel system intact helps the engine run as designed, which is part of operating the generator safely outdoors, far from windows, doors, and vents. See where your generator must be placed before you do anything else.

• Check the fuel system only when the engine is cold.
• Work outside, not in a garage or shed.
• Have a working CO alarm at home, as recommended by CPSC and CDC.

Prepare and stay safe before you start

Before touching any part of the fuel system, shut off the generator. If the engine has a fuel valve, turn it to the off position. Let the generator cool completely, because fuel can ignite on a hot engine or exhaust. Move the generator outdoors to an open area, away from the house, garage, and any structure. The CDC advises running generators outdoors more than 20 feet from windows, doors, and vents, and the same logic applies when you are inspecting the fuel system. You want fresh air and no confined space.

Keep the area clear of anything that could spark. Do not smoke, and keep any tools that create sparks away from the fuel tank and lines. A small leak can release vapor you cannot see. If you are working where fuel has spilled, let the vapor dissipate before continuing. Consider having a dry chemical or rated extinguisher nearby, though you should not rely on a fire extinguisher to make an unsafe inspection procedure acceptable.

Inspect the fuel tank

Start with the fuel tank itself. Look at the outside of the tank for wet spots, dark staining, or streaks of fuel running down the side. A damp area that smells of fuel is a leak even if you do not see dripping. Check the bottom of the tank, because small pin holes often form there, and the area around the fuel cap.

Inspect the fuel cap and its seal. A cracked cap or a missing gasket can let fuel slosh out during transport and can allow vapors to escape while the generator sits. Many tanks also have a vent in the cap. If the vent is clogged, pressure can build in the tank and push fuel past the cap seal or through a weak seam. If you cannot remove the cap to check the seal, at least look for fuel stains around the cap opening. The fuel tank is one of the most common places to find evidence of a slow leak, especially on an older generator.

If the generator has an external tank or a remote fuel supply, inspect that tank the same way, including the supply hose that connects it to the generator.

Inspect fuel lines and fittings

Trace the fuel line from the tank to the carburetor or fuel injection system. On many portable generators, the line is a short rubber or plastic hose with a clamp at each end. Look for cracks, cuts, brittleness, bulges, or areas where the outer layer is worn through. A fuel line that feels hard and brittle when you squeeze it is at the end of its life, even if it is not currently leaking.

Check every fitting and clamp. A loose clamp is one of the simplest causes of a fuel leak, and you can often fix it by tightening the clamp or replacing it with a fuel-rated clamp. Look for wetness around the barbed fittings where the hose meets the tank and the carburetor. Pay attention to the fuel filter if the generator has one in the line. A cracked filter housing or a loose connection at the filter can leak under pressure or vibration.

If the generator runs on dual fuel, it has additional fuel system components. For the propane or natural gas side, inspect the regulator hose and the connection at the tank. Propane is heavier than air and can pool in low spots, so a leak in the gas side is especially dangerous in an enclosed space. The EIA describes natural gas as mostly methane, which is lighter and disperses differently, but the risk is still real. For a generator that uses gasoline and propane, the fuel system check covers both sides. See how dual fuel generators differ if you are not familiar with the layout.

Look for the subtle signs

A fuel leak is not always a visible drip or puddle. Sometimes the only sign is a strong fuel smell around the generator, or a light oil sheen on the frame underneath the tank. Run your fingers along the underside of fuel lines and fittings. If you feel a wet film that smells like fuel, you have found the leak location. On rubber lines, a spot that is swollen or sticky can mean the fuel has soaked into the hose wall, which is a sign of deterioration.

On a generator that is not running, you can start the inspection by simply letting it sit for a few hours on a clean, flat surface, then looking under it for stains. If you want to be more thorough, place a clean drop cloth under the generator. Any fresh stain after the generator has been sitting still points to a fuel weep, because oil leaks behave differently and are usually not present on a new generator that has not been run.

What to do when you find a leak

If you find any sign of a leak, do not run the generator. A fuel leak that ignites can destroy the machine and can create a serious fire risk to anything nearby. Shut off the fuel valve if the generator has one. If the leak is at a loose clamp, you may be able to tighten it and then revisit the generator after an hour to re-check the area. If the leak is in a hose, replace the hose with a fuel-rated line that matches the manufacturer's specification. Do not use generic tubing that is not designed for fuel.

If the leak is in the tank itself, do not attempt a temporary patch. A patched tank can fail later, and even a small leak can create a fire hazard. Drain the tank and replace the tank or the generator, depending on the design. For a standby generator that is hard-wired and plumbed for fuel, a fuel leak is a reason to bring in a qualified service technician. If you are replacing parts yourself, turn off the fuel supply, work in a well-ventilated outdoor area, and allow the system to dry before you make any repair.

After you have made a repair, run the generator briefly, shut it off, and re-inspect the same areas. A leak that appears only when the engine runs and the fuel system is under pressure can be missed during a static check.

When to call a professional

Do it yourself only for the simple checks: a loose clamp, a cracked fuel line, or a worn cap gasket. Anything that involves the carburetor, the fuel pump, or an external fuel tank connection is best left to a mechanic, especially if you are not comfortable working with fuel. A small mistake on a fuel system can turn a routine check into a fire.

For a standby generator, the fuel system is often connected to a natural gas or propane supply. The Federal Register safety standard for portable generators exists in part because of the documented danger of carbon monoxide exposure, but a gas-connected standby unit has its own hazards. If you smell gas anywhere, do not operate the generator and call a qualified technician. If you are choosing a new generator, know the fuel system type before you buy. Read about gasoline vs. propane and natural gas fuel supply if you are comparing options.

What to pick for your use

Questions

How do I know if my generator has a fuel leak?

Look for wet spots, fuel stains, a fuel smell, or a sheen on the frame under the tank, along the fuel line, and at the fittings. If the generator has been sitting, place a clean cloth underneath it and check for stains after a few hours.

Can I run a generator with a small fuel leak?

No. A fuel leak creates a fire risk and can cause the engine to run incorrectly, which may increase carbon monoxide production. Shut off the fuel valve, find the leak, and repair it before the next run.

What should I do if I smell fuel but do not see a leak?

Shut off the generator and move it outdoors if it is not already. Check the cap seal, the underside of the tank, and the carburetor area. If you cannot locate the source, do not operate it and take it to a qualified service person.

How often should I check the fuel system for leaks?

Check the fuel system each time you change the oil, before seasonal use, and after the generator has been transported. More often if the generator is older or is used frequently. A quick visual check takes only a few minutes.

Is a propane generator leak different from a gasoline leak?

Yes. Propane is heavier than air and can pool in low areas, so even a small gas leak is dangerous in a garage or shed. Check the regulator hose and the tank connection, and if you smell gas, do not operate the generator and leave the area.

Can I use tape or a sealant to fix a leaking fuel line?

No. Tape and general-purpose sealants are not rated for fuel and can break down or move, causing a sudden larger leak. Replace the hose with a fuel-rated part that fits the manufacturer's specification.