Generator Fuel & Run-Time Guide
Stale gas kills more generators than every other cause combined. Here’s the fuel knowledge that keeps yours running — and running long.
I fueled fighter jets for 19 years, and if the Air Force taught me one thing it’s that fuel is a maintenance item, not just a consumable. Gasoline has a shelf life, carburetors have a memory, and run time is a math problem you can actually solve. This page covers all of it.
Gasoline Goes Bad in About 30 Days
Modern ethanol-blend pump gas starts oxidizing and absorbing moisture in roughly a month. The light ends evaporate, the leftovers turn to varnish, and that varnish plugs the pinhole jets inside your carburetor. This is the story behind most “ran fine last time” no-starts — the whole chain is laid out in Generator Starts Then Dies: The Carb Fix and Generator Surging? The Pilot Jet Fix.
The rules: stabilizer in every gas can the day you fill it, run the machine monthly so fresh fuel moves through the carb, and never store it wet — either drain the carb bowl or run it dry. Full storage routine: How to Store a Generator for the Off-Season.
Propane Never Goes Stale
This is dual-fuel’s superpower for outage duty. A propane tank filled five years ago burns exactly like one filled yesterday, and the fuel never touches a carburetor bowl. You give up 10–15% of rated wattage running on propane, but for a machine that sits 360 days a year waiting for a storm, that trade is a bargain.
How Long Will It Run? The Math
| Load | Typical Fuel Burn (5–8kW portable) | Per 5-Gallon Tank |
|---|---|---|
| 25% load | ~0.3–0.4 gal/hr | 12–16 hrs |
| 50% load | ~0.5–0.6 gal/hr | 8–10 hrs |
| Full load | ~0.8–1.0 gal/hr | 5–6 hrs |
Inverter generators change this math at light loads because they throttle the engine down to match demand — that’s how a 2,200-watt inverter runs all night on a gallon. For multi-day outage runs, the limit isn’t the engine, it’s the refuel cycle and the oil: How Long Can You Run a Generator Continuously.
Fuel Problems and Their Symptoms
Ethanol-Free: Worth It?
For a machine that sits, yes. Ethanol-free gas (sold as recreational fuel at some stations, or canned as TruFuel and similar) stores dramatically longer and doesn’t pull moisture into the fuel system. It costs more per gallon — I use pump gas plus stabilizer for regular running, and ethanol-free for the last tank before storage. Best of both without paying premium prices year-round.
Generator acting up right now?Run the Fix My Generator diagnostic — pick your symptom and I’ll walk you straight to the fix. →