How to read a fuel-economy claim

Plain definition

What “fuel economy” means

Fuel economy is how far a vehicle goes on a set amount of fuel, usually miles per gallon (MPG). A fuel-use rate is the reverse idea: how much fuel an engine burns in a set time, such as milliliters per minute (mL/min).

A generator test usually reports a fuel-use rate. A road test usually reports fuel economy. They are not the same number, so check which one a claim uses.

Plain definition

Even official numbers vary in real life

The US Environmental Protection Agency (EPA) rates cars with standardized tests. The government site FuelEconomy.gov says these ratings are useful for comparing vehicles but may not predict the MPG you will get.

It lists several things that change MPG: how and where you drive, vehicle condition and maintenance, fuel variations, vehicle variations, and engine break-in. Any before-and-after claim has to hold these steady.

Plain definition

Four questions to ask

1. What exactly was measured, and how? Weighing or timing the fuel is stronger than reading a dashboard estimate.

2. Was there a baseline — the same engine, same load, same route — run without the device?

3. How many runs, and under what conditions? Wind, temperature and load all move the number.

4. Who ran the test, and who supplied the hardware or paid for it?

Measured

An example that answers most of the questions

The Embry-Riddle test — an Embry-Riddle Aeronautical University master’s (M.S.) thesis (2026) — weighed and timed gasoline on each run of a small generator at about 2,760 watts (W) of load. Fuel use fell from 35.27 to 31.86 mL/min, a 9.67% lower fuel-use rate.

Its one-vehicle road test (a 1989 Chevrolet Blazer, 10 runs each way on a loop of about 20 miles) found about 8.7% better fuel economy. The thesis notes limits: only four of eight cylinders were covered, retrofit runs had high winds, and the manufacturer, Plasmoid Power, supplied the road-test hardware.

Seller claim

An example that leaves questions open

The seller’s Thunderstorm.tech test-results page reports a Clearwater, Florida generator test (June 24, 2024) with a 19.45% longer fuel run time, under a 2,400 W load. The page does not name the tester, and the units in its table are unclear.

This is shown as reported by the seller, not as a measurement this site can check.

Plain definition

Why the size of the number is not the point

A bigger percentage is not more convincing on its own. A modest number with a clear method, a baseline and named limits tells you more than a large number with none of those.