The most common generator failure has nothing to do with the generator. It is a machine that sat in a shed for fourteen months, with a half-tank of fuel that had turned to varnish in the carburetor. The homeowner pulls the cord at the start of an ice storm and nothing happens. The fix, by then, is a messy repair in the cold.
Fuel is the part of backup power that is easiest to ignore and hardest to improvise. This guide explains the three common fuel options, how to store them safely, what regular maintenance keeps a generator ready and how to plan fuel for an outage that lasts longer than a day. It stays at the level of what any owner should know. Your manual is the authority on your machine, and a service technician is the right person for repairs.
A homeowner pulls the cord at the start of an ice storm and nothing happens. The tank holds fourteen-month-old gasoline, and the carburetor is full of varnish. The generator was fine; the fuel plan was missing.
The three common fuels
Gasoline
Gasoline is the default for portable generators. It is easy to buy, cheap per unit of energy and available at most stations, though not necessarily during a widespread outage when pumps cannot operate.
Widely available, high energy content, and many models run on it.
It degrades. Standard gasoline blended with ethanol can begin to break down in a month or two, forming gum and varnish that clog small passages. It is also highly flammable, and storing it carries risks.
Propane
Propane stores in tanks that can sit for years without degrading. It burns cleanly and does not gum up the carburetor.
Long shelf life, cleaner combustion, easy to store in standard cylinders.
Slightly lower output from the same engine, fuel consumption can be higher by volume, and cold weather can reduce vaporization in small cylinders. A standard cylinder holds limited energy.
Natural gas
Natural gas is available on standby units and some portable models with conversion kits, supplied from the home’s gas line.
No tank to refill and potentially unlimited runtime while the supply is working.
It depends on the gas utility staying up. Output is lower than with gasoline on the same engine. Connection to the home’s piping is regulated and must be done by licensed professionals.
Dual and tri-fuel machines
Some portable generators can run on gasoline and propane, and some on all three. They are a flexible choice: you can keep propane for emergencies and use gasoline when it is available. Check the output on each fuel; it is often lower on propane.
Comparing fuels
| Factor | Gasoline | Propane | Natural gas |
|---|---|---|---|
| Shelf life | Weeks to months, longer with stabilizer | Years | Not stored |
| Handling risk | High, very flammable liquid | Moderate, pressurized gas | Piped, professional installation |
| Output compared with gasoline | Full | Slightly lower | Lower |
| Availability in a regional outage | May be limited | Stored supply helps | Depends on the utility |
| Suits | Portable use with rotation | Long-term storage | Standby installation |
Storing gasoline safely
If you use gasoline, the rules are straightforward.
- designed for fuel, clearly marked and with a spout that seals.
- such as in a detached shed or well-ventilated outbuilding, away from ignition sources, pilot lights and water heaters. Never store fuel in a basement or a living area. Check local fire codes about quantities.
- and away from heat.
- Leave expansion space.
- so you can use the oldest first.
- Use stored fuel in your car and replace it with fresh fuel every few months.
- Fuel stabilizers can extend storage life when used as directed on the label. Follow the product’s instructions exactly.
We do not advise on quantities allowed by your local fire code. Ask your fire department.
Storing propane
Propane cylinders should be stored upright, outdoors, in a ventilated area, away from ignition sources and not in a basement or garage attached to the house. Do not store them in a vehicle. Follow cylinder safety markings and local rules. Check the cylinder’s expiry date and condition. Never modify valves or fittings, and have any leak checked by a professional immediately.
Maintenance that keeps a generator ready
A generator is a small engine and needs the same attention as a lawn mower or a car, even though it rarely runs. The manual contains the schedule. In general:
- at the intervals stated, and check the level before every run.
- at the recommended interval.
- Look for leaks, cracks and clogged filters.
- Start the machine every month or two and run it under a modest load for the time the manual suggests. That circulates oil and keeps the fuel system moving.
- and covered appropriately.
- on electric-start units and charge as needed.
- on a tag attached to the generator.
For standby units, an annual service by an authorized technician is standard practice and often required to maintain the warranty.
Stale fuel: the usual culprit
If a machine will sit unused, there are two common approaches. One is to drain the fuel system according to the manual, so no gasoline is left to degrade. The other is to treat the fuel with a stabilizer and run the engine long enough for it to circulate. Never drain fuel indoors or near ignition sources, and dispose of old fuel at a proper facility rather than pouring it onto the ground or down a drain.
Planning fuel for an outage
Fuel planning is arithmetic. Manufacturers publish run times at different loads. Suppose a generator burns about a gallon every five hours at half load. A 48-hour outage then needs around ten gallons, plus a margin. Multiply by the number of days you want to be prepared for, and compare with what you can safely store.
Remember that refueling a hot generator is dangerous. Let the engine cool before adding fuel, as the manual instructs, and never refuel while it is running. In a long outage, fuel stations may be closed, so a plan for rotating stored fuel and a propane backup are worth considering.
Refueling and operating safely
- Run generators outdoors only, well away from windows, doors and vents, in the open.
- Keep them on a flat, dry surface under a vented cover or canopy designed for generators, as the manual allows.
- Use a carbon monoxide alarm inside the house, with fresh batteries.
- Let the engine cool before refueling.
- Keep children and pets away from the machine.
For the load list that decides how much fuel you burn, see our guide on sizing a generator. For how the generator connects to the house, see transfer switches and safe hookup.
The short version
Fuel is the weak link. Gasoline is convenient and perishable, propane keeps for years and natural gas depends on the utility. Store fuel safely outdoors in approved containers, rotate it, run the generator regularly and follow the maintenance schedule. A machine that starts on the first pull in the dark is the result of unglamorous habits practiced in calm weather.
Key takeaways
- Propane keeps for years; untreated gasoline does not.
- Run the generator under load every month or two.
- Store fuel outdoors in approved containers and rotate it.
- Let the engine cool before refueling.
Related: how to size a generator tells you how much fuel a given load will burn.
