How to Stabilize Gas in a Generator for Long-Term Storage
The most common reason a generator will not start after months of storage is not a broken part. It is old gasoline. Fuel degrades faster than most people expect, and ethanol-blended pump gas makes it worse. The residue left behind clogs the carburetor, and suddenly a generator that worked fine last winter will not run when you need it.
This guide explains why fuel goes bad, two safe ways to prepare a generator for storage, and how to choose a stabilizer.
Why Gasoline Goes Bad in Storage
- Oxidation. Gasoline slowly reacts with air, forming gums and varnish that clog small passages.
- Ethanol. Most pump gas contains up to 10 percent ethanol, which attracts moisture from the air. Over time this can cause phase separation, where water and ethanol settle out of the fuel, and can lead to corrosion and poor running.
- Evaporation. The lighter, more volatile parts of the fuel evaporate, leaving fuel that is harder to ignite.
Untreated gasoline can start to degrade in a matter of weeks to a few months, which is why a generator that sat all summer is a classic no-start.
Two Ways to Prepare a Generator for Storage
Option 1: Treat the fuel with a stabilizer (best for emergency generators)
If you want your generator ready to run on short notice, keeping fuel stabilized in the tank is the practical approach.
- Use fresh gasoline. Stabilizer slows degradation, but it cannot restore old fuel. Start with fresh fuel.
- Add the stabilizer according to the label’s ratio, ideally to the tank before or as you fill it so it mixes well.
- Run the engine for 5 to 10 minutes outdoors so the treated fuel reaches the carburetor and fuel lines.
- Fill the tank mostly full to limit air space and moisture. Leave a little room for expansion.
- Store the generator in a dry, ventilated place, away from ignition sources, with the fuel valve in the position recommended by the manual.
Option 2: Drain the fuel system (best for long, planned storage)
For storage over many months with no outage risk, many people prefer to remove the fuel entirely.
- Turn off the fuel valve if your generator has one and let the engine run until it stops, which burns the fuel in the carburetor. Follow your manual’s instructions.
- Drain the tank into an approved container, outdoors and away from ignition sources.
- Drain the carburetor bowl if the model has a drain screw, again into a container.
- Dispose of or use the old fuel appropriately, for example by mixing small amounts into a vehicle’s tank if your local guidance allows. Do not pour it on the ground or down a drain.
Choosing a Fuel Stabilizer
- Ethanol protection. Look for products designed for ethanol-blended fuel.
- Storage claims. Many stabilizers claim protection for 12 to 24 months. Check the label, and still rotate your fuel regularly.
- Correct dosing. More is not better. Follow the label’s ratio.
- Compatibility. Make sure it is suitable for small four-stroke engines.
Recommended Products
STA-BIL 360 Protection is a widely used fuel stabilizer that is formulated for ethanol-blended gasoline, with protection against gum, varnish, and corrosion. It is an easy option for treating a generator’s tank before storage. #CommissionsEarned
Sea Foam Motor Treatment is a petroleum-based additive used as a fuel stabilizer and cleaner in small engines, and it is popular for helping keep fuel systems clean during storage. Follow the label instructions for the correct ratio. #CommissionsEarned
Star Tron Enzyme Fuel Treatment is an enzyme-based additive designed to condition fuel and help with ethanol-related problems, and it is a common choice for stored equipment. #CommissionsEarned
If you would rather skip pump gas entirely, TruFuel is a pre-mixed, ethanol-free fuel in cans that stores well and is popular for generators and other small engines that sit unused. It costs more per gallon than pump gas, but it can be a worthwhile option for a generator that rarely runs. #CommissionsEarned
For safe fuel handling, a Scepter 5-gallon fuel container is a reliable, approved container for storing and transferring gasoline without spills. #CommissionsEarned
Quick Comparison Table
| Product | Type | Best For |
|---|---|---|
| STA-BIL 360 Protection | Stabilizer | General long-term storage, ethanol fuel |
| Sea Foam Motor Treatment | Stabilizer / cleaner | Keeping fuel systems clean in small engines |
| Star Tron Enzyme Fuel Treatment | Enzyme fuel conditioner | Ethanol-related fuel problems |
| TruFuel | Ethanol-free pre-mixed fuel | Rarely-used generators |
Storage Checklist
- Use fresh fuel and the correct stabilizer dose.
- Run the engine to circulate treated fuel through the system.
- Change the oil if it is due, since used oil can contain acids and contaminants.
- Remove the battery on electric-start models, or put it on a maintainer.
- Cover the generator with a breathable cover once it is fully cool.
- Store in a dry, ventilated location away from heat and ignition sources.
- Start and run it for a short time every one to three months if you can.
Common Mistakes to Avoid
Adding stabilizer to old, stale fuel. It cannot restore degraded gasoline. Start with fresh fuel.
Not running the engine after adding stabilizer. Treated fuel must reach the carburetor to protect it.
Overdosing the additive. Follow the label.
Storing fuel in unapproved containers. Use proper fuel cans, and store them away from ignition sources.
Forgetting the battery. A dead starting battery is the next most common no-start cause.
FAQ
How long does gas last in a generator?
Untreated gas can degrade within weeks to a few months. With a stabilizer, many products claim 12 to 24 months, but regular rotation is still a good habit.
Should I drain the fuel or use stabilizer?
Stabilizer is better if you want the generator ready for outages. Draining is better for long, planned storage with no emergency use.
Does ethanol-free gas need stabilizer?
It lasts longer, but still degrades over time, so a stabilizer is still useful for long storage.
Can I just run the carburetor dry?
Many people do, and it can work, but some stored fuel in the tank may still go bad. Follow your generator’s manual.
How often should I run my generator in storage?
Every one to three months for 10 to 20 minutes under light load is a common recommendation.
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