If you’re looking to get power and fuel economy gains out of your car, chances are you’ve probably seen one of the online, including the HHO generator. But do HHO generators work or do they only lighten your wallet?

These things were super popular over a decade ago when fuel prices were high and people with gas-guzzling vehicles were trying trying to find a way to ease the pain at the pump.

These generators often come with amazing claims like a 35 percent gain in fuel economy, more horsepower, less emissions, extended engine life and even a cooler-running engine. You get all of that for about $200. It sounds too good to be true.

The took a crack at this mystery by setting up an HHO generator in a Chevrolet Suburban and a generator.

Oxyhydrogen (HHO) generators work by taking power from your car’s battery or alternator to run a current through electrodes into water mixed with an electrolyte. The result is that the water molecules split into hydrogen and oxygen, making oxyhydrogen gas. From there, the gas gets inserted into the engine from the intake. This gas is explosive enough that an internal combustion engine can run on it.

Effects on the Suburban were measured over 250 miles and included acceleration times before and after installation of the HHO generator. Unfortunately, not only did the generator not increase performance, but it didn’t clean the SUV’s engine, either.

The generator was used for a fuel economy test. Surely the HHO would make a difference here since it only has to help a small engine.

In this test, the generator was first run dry on regular fuel as a baseline then run on the HHO and fuel mix for comparison. Unsurprising by now, but the HHO generator failed to increase the fuel economy of the generator.

As another test, the Project Farm host used double the recommended amount of potassium hydroxide (the electrolyte), but still failed to see any results.

So what gives? If hydrogen can make an engine run, why doesn’t it work with a kit purchased from eBay?

Back in 2009, Popular Mechanics, with the help of NBC’s Dateline up with all of the silly fuel-saving gadgets and found that not a single one of them did a thing except waste $1,900. In fact, the HHO generator drew 15 amps of power from the car and it couldn’t make enough oxyhydrogen gas to break even.

Mythbusters tested an HHO generator over a decade ago and found that while oxyhydrogen gas can power a car’s engine, the HHO generator that they used made no impact.

A more modern study in the Alexandria Engineering Journal found that it is possible to see some fuel economy gains using an HHO generator, but the researchers custom fabricated a unit that was optimized for the test vehicle.

Is it possible to get your car to burn hydrogen gas? Sure. But as Project Farm and other tests show, an HHO generator from eBay really isn’t going to cut it.

(Updated 3/3/22 with new details)