Off-the-Shelf Fuel Additives: Magic Potion or Snake Oil?

The Shelf of Promises

Walk down the automotive aisle of any supermarket or parts store, and you will see dozens of small bottles promising miracles. Fuel additives, such as Redex, STP, and Wynns, claim to clean your fuel injectors, reduce emissions, and drastically improve your fuel economy. But are they worth pouring into your tank?

The Chemistry Behind the Bottle

These pour-in additives are primarily composed of concentrated detergents, such as Polyetheramine (PEA) or Polyisobutene amine (PIBA). These are the exact same cleaning agents that major fuel brands inject into their premium fuels at the refinery.

When you pour a bottle into your tank, the concentrated chemicals run through your fuel lines and injectors, breaking down minor carbon deposits and varnish. If you are driving an older car with 80,000+ miles that has never had its injectors cleaned, you will likely notice a smoother idle and a slight bump in MPG after a treatment.

The Cost-Benefit Analysis

While the chemicals do work, the economics often don't make sense. A single bottle of fuel injector cleaner can cost between £5 and £10, and it treats one tank of fuel.

Alternatively, you could use the FindPetrol price map to find the absolute cheapest premium unleaded or premium diesel in your area. Filling up with a tank of premium fuel (which already contains these exact same detergents) will usually only cost you £4 to £6 extra per tank-making it a cheaper and more effective way to clean your engine than buying an off-the-shelf bottle.

Local prices differ far more than most drivers expect. For a worked example, see current petrol prices in Edinburgh.

Where to find the cheapest fuel near you

Supermarket forecourts usually undercut the oil majors, but the gap varies enormously by town - a competitive independent will often beat a supermarket that has no rivals nearby. You can compare every UK fuel brand side by side, or search your postcode to find the cheapest petrol near me right now. The UK average is currently 161.4p a litre across 7,916 stations.