How to Clean a Generator Fuel Tank

Why Clean the Generator Fuel Tank?

Over time, fuel in a generator tank can break down and leave varnish, sediment, or water behind. Rust can form on the inside of a steel tank, and debris can collect around the fuel outlet. When that material reaches the fuel valve, filter, or carburetor, fuel flow becomes uneven and the generator may stall under load or refuse to start. Cleaning the tank restores fuel flow and often fixes rough running without replacing parts. If you are deciding whether to buy a new generator, a tank you can drain and inspect is easier to maintain; portable generators vary in tank access and fuel system design.

Look for these signs that the tank needs attention:

• Fuel that smells sour or looks dark and cloudy
• Sediment or rust flakes in the tank or in the fuel filter
• The generator starts, then dies after running briefly
• Surging or stumbling when a load is applied
• Fuel stains around the cap, fuel lines, or tank seams

Safety Before You Start

Fuel tank cleaning starts with fuel safety. Work outside or in a very well-ventilated area, away from open flames, pilot lights, sparks, and anything that can ignite fuel vapor. Keep a fire extinguisher nearby and put oily rags in a metal container. Do not smoke. Let the engine cool completely before opening the fuel system. Before you touch the tank, close the fuel shutoff valve if your generator has one, and disconnect the spark plug wire on a pull-start engine. On electric-start models, disconnect the battery to prevent accidental starting. See generator electric start battery if your model has a battery.

Never run the generator indoors while you work on the fuel system. The U.S. Consumer Product Safety Commission warns that portable generators should never be operated inside homes, garages, basements, or sheds. The CDC describes carbon monoxide as an odorless, colorless gas that kills without warning, and the EPA warns that it can be fatal at high concentrations. Do all fuel work in open air and keep generator exhaust away from windows, doors, and vents.

Drain the Fuel Tank

Start by draining the old fuel. Remove the fuel cap and use a hand siphon or pump to empty the tank into an approved portable fuel container. If the tank has a drain or a removable fuel line, you can let the remaining fuel flow out through the fuel valve. Do not pour fuel on the ground. Dispose of old fuel according to local rules, and do not mix it with new fuel.

Follow these steps to drain the tank completely:

• Turn the fuel shutoff valve to the off position if your generator has one.
• Disconnect the fuel line at the tank or carburetor, and label or photograph where each line goes.
• Drain the tank fully so no fuel remains when you flush it.
• If the tank is mounted with bolts or straps, remove it for easier inspection. Some generators have an external pickup tube; related fuel plumbing is covered in how to install external fuel tank kit.
• Empty the fuel sediment bowl if your generator has one; see how to replace generator fuel sediment bowl.

Flush the Tank and Remove Debris

With the tank empty, flush it with fresh fuel or a commercial fuel-tank cleaner. Pour a small amount into the tank, swirl it around, and pour it out through the fuel valve. Repeat until the liquid comes out clear. For varnish and gum, let the cleaner sit for the time stated on the product label before draining. Do not use water or soap. Water left in a fuel tank can cause rust and make the engine run poorly. If you removed the tank, wipe the inside with a lint-free cloth.

Use these guidelines while flushing:

• Use a soft nylon brush to loosen sediment from the bottom and corners.
• Inspect the pickup screen or fuel filter at the tank outlet, and clean or replace it if clogged. See how to replace generator fuel filter.
• Check the fuel cap vent for dirt; a blocked vent can stop fuel flow. See how to clean generator fuel cap vent.
• For a steel tank, remove loose rust with fine steel wool or a wire brush. For a plastic tank, use plastic-safe abrasives only; steel wool can scratch the surface and create rough spots where debris collects.

Remove Rust and Decide Whether to Repair

Surface rust on the inside of a steel tank can be cleaned if it is light and flaky. Wipe away loose particles and rinse again with fresh fuel. If you see pitting or holes, or if rust keeps forming after cleaning, replace the tank. A repaired tank can shed new debris into the fuel system and cause the same problem again. Many portable generators use plastic or coated steel tanks; tank material affects how you clean and how much rust you are likely to see. See generator fuel tank material.

If the tank is badly rusted, the reliable fix is a new tank or, for some generators, a replacement fuel system. If you are shopping, look for a generator with a fuel system that is simple to service. Compare dual fuel generators if fuel storage and tank maintenance are part of your decision.

Reassemble, Test, and Prevent a Repeat

Reconnect the fuel lines, tighten clamps, and reinstall the tank. Fill the tank with fresh fuel and check every connection for leaks before you start the engine. A leak at the tank outlet or fuel line can become a fire hazard. If you added or replaced a fuel filter, install it in the correct direction. Start the generator outdoors and let it run briefly with a small load to confirm steady fuel flow.

To keep the tank clean longer:

• Use fresh fuel and add a fuel stabilizer before storage. See generator fuel stabilizer and storage life.
• Drain the tank before long periods of storage, especially if the generator will sit for months. See generator storage preparation.
• Keep the fuel cap vent clean and avoid letting water enter the tank.
• If the carburetor also has old fuel residue, clean it while the fuel system is apart.

What to pick for your use

Questions

How often should a generator fuel tank be cleaned?

There is no fixed interval. Clean it when you see rust, sediment, or varnish, whenever fuel flow becomes uneven, or after the generator has sat with untreated fuel for a long time. For seasonal use, drain or stabilize fuel before storage to reduce the need for cleaning.

Can I clean the tank without removing it from the generator?

Yes, if the tank is easy to reach and you can drain it fully. Flush with fresh fuel or a fuel-tank cleaner and drain through the fuel valve. Removing the tank makes it easier to inspect and scrub the inside. If the tank is part of the frame or has a complex shape, removal may not be practical; use a flexible pick-up tool and inspect with a flashlight.

What dissolves old gas varnish?

Commercial fuel system cleaners are formulated for varnish and gum. You can also use fresh fuel as a flush for loose debris. For stubborn deposits, follow the cleaner instructions and give the solvent time to soften the residue. Avoid water-based cleaners or soapy water, since water left in a fuel tank can cause rust and fuel delivery problems.

Will rust in the fuel tank ruin my generator?

Rust can clog the fuel filter, fuel lines, and carburetor jets, which can make the generator stall or refuse to start. Remove loose rust with a brush for steel tanks. If rust has eaten through the metal, replace the tank instead of patching it. You can read more in generator troubleshooting won't start.

Is it safe to clean a generator fuel tank indoors?

No. Fuel vapors and carbon monoxide are dangerous. Do all fuel work outside, away from ignition sources, and never run the generator indoors. The U.S. Consumer Product Safety Commission says portable generators should never be used inside homes, garages, basements, or sheds. See generator safety checklist outdoor use.

Should I clean the carburetor at the same time?

If the generator sat with old fuel, the carburetor may also have varnish. Cleaning the tank is a good start, but fuel drawn from a clean tank still passes through the carburetor. If the engine runs rough after tank cleaning, inspect the carburetor and fuel filter.