Go to any auto-parts store and you'll find a whole shelf of bottles and plug-in gadgets promising "10 to 25% more MPG." Some are built on real chemistry. Most are marketing with a federal-trade-commission history. Here's the short version of what's actually worth your money.
Top-tier injector cleaners — these work
The strongest consensus in independent testing (Consumer Reports, SAE technical papers, fueleconomy.gov) is around injector cleaners based on polyetheramine (PEA). Brand names include Chevron Techron, Red Line SI-1, Gumout Regane, and BG 44K. These meaningfully dissolve carbon deposits on intake valves and injectors.
Expected effect: on a car with 60,000+ miles that's never had one, 2 to 4% MPG recovery is realistic. On a well-maintained car, essentially zero — there's nothing for the cleaner to clean. Not a miracle, but cheap and worth doing every 10,000 miles on older cars.
Octane boosters — mostly not what you think
Octane boosters raise the anti-knock rating of gasoline. For cars that require premium, a bottle of octane booster added to regular gas will prevent pinging, but it's more expensive per octane point than just buying premium.
For cars that run regular (the vast majority), octane booster does nothing for fuel economy — your engine management doesn't advance timing beyond what the knock sensor says is safe at 87 octane. Skip them unless you're running an older high-compression engine in a hot climate.
Ethanol treatments — situational
Products like Star Tron, StaBil Marine, or similar ethanol-specific treatments matter mostly for cars that sit — boats, motorcycles, snow-blowers, the summer car in the garage. They prevent phase separation (where water and ethanol absorb each other and settle out of gasoline) during long storage.
For daily-driven cars that cycle through fuel every week or two, ethanol treatment does very little. Good to have on the shelf if you have a lawn mower or a boat.
Magnet clips on the fuel line — pure placebo
Magnetic "fuel ionizers" clipped to the steel fuel line are a classic pseudoscience product. Gasoline is not magnetic, its molecules are not meaningfully affected by neodymium at room temperature, and independent testing has never shown any measurable MPG change.
The same applies to air-intake "turbulators," exhaust-tip "resonators," and "fuel line water separators" sold at flea markets. If the physics would need to be wrong for the product to work, the product doesn't work.
| Product | Real MPG effect | Verdict |
|---|---|---|
| PEA injector cleaner (older car, 60k+ mi) | +2–4% | Worth it — every ~10k mi |
| PEA injector cleaner (well-maintained) | ~0% | Skip — nothing to clean |
| Octane booster (regular-gas car) | 0% | Skip |
| Ethanol treatment (daily driver) | 0% | Skip |
| Ethanol treatment (stored vehicle) | N/A | Worth it for boats/mowers |
| Fuel-line magnets / "ionizers" | 0% | Avoid — pseudoscience |
| Air-intake turbulators / vortex chips | 0% | Avoid |
The takeaway
Save your money. A $10 bottle of polyetheramine injector cleaner every 10,000 miles on an older car is the only over-the-counter fuel-additive product with broad independent support. Everything else sold as a "fuel saver" is either marketing a real maintenance item under a dramatic label, or simply not doing anything at all.
