How to Winterize a Generator for Cold Weather Storage

Why Winterizing Matters More Than Most Owners Realize

The number one cause of generator failure at startup is a carburetor clogged with varnish from stale gasoline left sitting in the fuel system over winter. It happens to thousands of homeowners every year — the power goes out in January, they pull out the generator, and it will not start. Or it runs rough, stumbles under load, and dies within minutes.

Proper winterization takes less than 30 minutes and costs almost nothing. Carburetor cleaning or replacement after the fact costs $100 to $400 and requires a repair shop visit. The math is simple.

When to Winterize

Winterize your portable generator when you expect it to sit unused for more than 30 days — particularly going into fall and early winter. In regions where generators see active use during winter ice storms, you may choose to keep the generator in service-ready condition year-round instead, which involves a different maintenance approach covered below.

The critical trigger is not temperature — it is time. Ethanol-blend gasoline (standard at most U.S. pumps) begins to absorb moisture and phase-separate in as little as 30 days. The gummy residue left behind as it degrades is what clogs carburetor jets and passages.

Method 1: Fuel Stabilizer (Recommended for Most Homeowners)

For generators that will be stored for 30 days to 12 months, fuel stabilizer is the simplest and most effective solution.

1. Add stabilizer to a fresh tank of fuel. Do this at the pump or immediately after filling. Do not add stabilizer to gasoline that has already been sitting — stabilizer slows degradation but cannot reverse it. Use STA-BIL 360 or PRI-G at the manufacturer’s recommended ratio (typically 1 oz per 2.5 gallons).
2. Run the generator for 10 to 15 minutes. This circulates the stabilizer-treated fuel through the carburetor, fuel lines, and all passages — not just the tank. This step is critical and often skipped. Stabilizer only protects fuel it has reached.
3. Shut down normally and store. The stabilizer-treated fuel in the system will resist varnish formation for 12 to 24 months depending on the product used.

Method 2: Run the Fuel System Dry (Best for Long-Term Storage)

For generators stored longer than 12 months, or for homeowners who prefer to store without any fuel in the system, running the carburetor dry is the most reliable approach.

1. Turn the fuel shutoff valve to OFF (if your generator has one — most do).
2. Start the generator and let it run until it runs out of fuel and dies on its own. This depletes the carburetor bowl and fuel passages of all gasoline.
3. For generators without a shutoff valve: Run the generator until it is almost out of fuel, then remove the carburetor bowl drain screw and drain any remaining fuel from the float bowl.
4. Drain the fuel tank completely using a hand pump or by tipping the generator (check your manual — not all generators can be tipped safely). Store any drained fuel separately in a treated container if it is still fresh.

Additional Winterization Steps

Change the Oil Before Storage

Used engine oil contains combustion byproducts, moisture, and acids that accelerate corrosion of internal engine components during storage. Changing the oil before storing the generator — rather than after — means the engine sits on fresh, clean oil all winter. This is one of the most overlooked and highest-value maintenance steps for generator longevity.

Remove or Charge the Battery

Electric-start generators have a battery that will self-discharge over winter. A battery discharged to zero and left cold can suffer permanent capacity loss or freeze damage. Options:

• Remove the battery and store it indoors in a climate-controlled space, connected to a battery tender/maintainer.
• Leave it connected and use a float charger to maintain charge level through winter.
• At minimum, disconnect the negative terminal to slow self-discharge.

Fog the Cylinder (Optional but Recommended for Long Storage)

Fogging oil is a preservative spray that coats the cylinder walls, piston, and valve surfaces to prevent rust during extended storage. To apply it:

1. Remove the spark plug.
2. Spray a 2-second burst of fogging oil into the spark plug hole.
3. Pull the recoil starter slowly 3 to 4 times to distribute the oil across the cylinder walls.
4. Reinstall the spark plug.

Clean the Air Filter

Inspect the air filter before storage. A foam filter element can be washed with mild soap, dried completely, and lightly oiled with clean motor oil before reinstalling. Paper elements that are visibly dirty should be replaced — do not start the storage season with a compromised air filter.

Cover and Store Properly

Store the generator in a dry, ventilated location — a garage or shed is fine, never indoors in a living space. Use a fitted generator cover to keep dust and moisture off the unit. Do not wrap it in a tarp that traps moisture inside.

Preparing the Generator for Spring — De-Winterizing

Before the first use after winter storage:

1. Check engine oil level — top up if needed.
2. Inspect the air filter — clean or replace as needed.
3. Check the spark plug — clean or replace if fouled.
4. If you ran the fuel dry: refill with fresh fuel before starting.
5. If you used stabilizer: the stabilized fuel is ready to use — just start it up.
6. Start the generator and let it run unloaded for 5 to 10 minutes to circulate oil and confirm it is running smoothly before connecting any load.

Bottom Line

Winterizing a generator is a 30-minute job that protects a machine worth hundreds or thousands of dollars. Use fuel stabilizer for storage up to 12 months, run the system dry for longer storage, change the oil before you put it away, and tend to the battery. Do this every fall and your generator will start reliably every spring — and every time the power goes out in between.