How Long Can Gas Sit in a Generator Before It Goes Bad?

Jun 08, 2025

Left petrol in your camping generator since last summer? Bad news: petrol goes off in as little as 3–6 months. That means clogged carbs and zero power when you need it most. Want to avoid a dead generator and ruined trip? Here’s how to store fuel right and keep things running.

Understanding Gasoline's Shelf Life in Your Generator

The Core Question: How Long Does Untreated Gas Last?

Typical Lifespan of Standard Gasoline (e.g., 30–90 days)

Petrol doesn’t stay fresh forever.

On average, regular petrol lasts 3 to 6 months if it’s stored correctly. After this point, it starts to break down and lose efficiency.

This can make it harder to start your generator or reduce its power output.

Factors That Degrade Fuel Quality (Oxidation, Evaporation, Contamination)

Fuel begins to degrade as soon as it's refined.

Oxidation, evaporation of light hydrocarbons, and contamination all contribute. Exposure to air and moisture speeds up the process.

As a result, the fuel loses its ability to burn cleanly and efficiently.

Champion 3600 generator with yellow frame and black engine, on a white background.

The Special Case of Ethanol-Blended Fuel (E10) and Its Impact

Ethanol-blended fuels like E10 break down faster than pure petrol.

Ethanol attracts moisture, which can lead to fuel separation and microbial growth.

This process often starts within 30 days, especially in humid conditions.

Telltale Signs Your Generator Fuel Has Gone Bad (Smell, Appearance, Performance)

There are a few common signs that your generator fuel may have gone off:

Difficulty starting
Rough or inconsistent running
Sour or varnish-like smell
Cloudy fuel or visible sediment

If you notice any of these, it’s time to drain the tank and refill with fresh petrol.

The Risks: What Happens When You Use Old Fuel?

Common Generator Problems Caused by Bad Gas (Hard Starting, Stalling)

Using stale petrol can lead to frustrating issues.

Hard starting, sputtering, or the generator shutting off unexpectedly are all common.

Even if it starts, power output may be unreliable.

Champion 3500 watt inverter generator with handle and wheels, on a white background.

Potential for Clogged Carburettors and Fuel Lines

Old petrol leaves behind sticky residues.

These can clog the carburettor or fuel lines, restricting fuel flow. If ignored, this may require cleaning or part replacement.

Long-Term Engine Damage and Reduced Generator Lifespan

Continually running on degraded fuel can corrode engine components.

This shortens your generator’s lifespan and may lead to costly repairs.

It’s a risk that’s easily avoided with simple fuel care.

Extending Fuel Life and Protecting Your Generator Investment

Proactive Strategies for Long-Lasting Fuel

The Role and Benefits of Fuel Stabilisers (How They Work, How Long They Extend Life)

Fuel stabilisers help slow the natural breakdown of petrol.

They protect against oxidation, reduce water absorption, and control microbial growth. Some can keep petrol stable for up to 24 months.

Best Practices for Adding Fuel Stabiliser

Always add stabiliser to fresh petrol.

Follow the manufacturer’s dosage instructions and run the generator briefly to circulate the treated fuel.

This protects internal parts and ensures the stabiliser mixes properly.

Choosing the Right Fuel: Considering Non-Ethanol Options

Where available, non-ethanol petrol is ideal for long-term storage.

It doesn’t absorb moisture as readily and tends to degrade more slowly than ethanol blends.

Proper Storage and Maintenance for Optimal Fuel Health

Ideal Fuel Storage Containers and Conditions (Sealed, Cool, Dry)

Store petrol in clean, approved containers.

Keep them tightly sealed and labelled with the storage date. Place them in a cool, dry spot away from direct sunlight.

Good storage prevents evaporation and contamination.

Generator Storage Prep: Running the Carburettor Dry vs. Full Tank with Stabiliser

If storing for more than a month, choose one of these methods:

Drain the carburettor after running the engine
Or store with a full tank of stabilised fuel to reduce condensation

Both methods help preserve engine health over time.

The Importance of Regular Generator Exercise (Monthly Runs)

Running your generator for a few minutes each month keeps parts lubricated.

It also allows you to spot problems before they become serious. Even if you're not using it, this simple habit makes a big difference.

Champion 3600 generator operating beside a motorhome on grass, with extension cords plugged in.

Dealing with Old Fuel: Disposal and Alternatives

How to Safely Dispose of Contaminated or Old Gasoline

Never pour old petrol down drains or into the ground.

Check with local recycling centres or hazardous waste facilities for proper disposal. Many accept small amounts of old fuel for safe processing.

Brief Mention: Fuel Alternatives with Longer Shelf Lives (e.g., Propane)

Propane is a great low-maintenance alternative.

It doesn’t degrade like petrol and can be stored indefinitely when sealed properly. Ideal for occasional users or backup-only systems.

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