Should You Use Fuel Additives? What Mechanics Say

When it comes to keeping your engine purring, fuel additives often get tossed around as a quick fix or performance booster. But do they really work? Or are they just another bottle of snake oil on the shelf?

As a mechanic who’s spent more hours under bonnets than I care to count, I’m here to cut through the fumes and give you the straight facts about fuel additives, what they do, when to use them, and whether they’re worth your money.

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What Are Fuel Additives?

Fuel additives are chemical compounds you pour into your tank to improve your vehicle’s performance, fuel efficiency, or engine health. Some are designed to clean the fuel system, others to boost octane or prevent corrosion, and a few even claim to reduce emissions.

They usually come in small bottles, cost anywhere from £5 to £20, and can be found in most garages, parts shops, and even supermarkets.

Types of Fuel Additives

Here’s a quick breakdown of the most common types:

• Fuel System Cleaners: Target carbon build up in injectors, valves, and combustion chambers.

• Octane Boosters: Increase the octane level of petrol to improve combustion.

• Diesel Additives: Improve lubrication, prevent gelling in winter, or clean diesel injectors.

• Injector Cleaners: Focused on clearing clogged fuel injectors for better spray patterns.

• Anti Corrosion Additives: Protect metal components, especially in older or stored vehicles.

Do They Actually Work?

Now for the meat of it: sometimes they do, but not always.

According to most seasoned mechanics, fuel system cleaners can be effective if your car’s running rough due to carbon deposits or dirty injectors. A decent cleaner can restore lost performance and smooth out idling issues.

Octane boosters, on the other hand, tend to be overhyped unless you’ve got a high performance engine that specifically calls for higher octane than what’s at the pump. Using these in a standard hatchback? You’re likely wasting your money.

For diesel drivers, additives that prevent waxing (fuel gelling in cold weather) or increase cetane levels can make a real difference, especially in winter or if you’re running older engines.

But for the average motorist who fills up regularly with decent fuel and keeps up with service intervals? Additives are usually unnecessary.

What the Mechanics Say

I’ve spoken with dozens of mechanics across the UK, from MOT testers to race technicians, and here’s what most agree on:

“Additives aren’t magic. If your car’s well maintained, you shouldn’t need them. But if it’s an older motor or you’ve been skimping on services, a good cleaner might help.”

“Cheap fuel can lead to carbon build up, especially in city cars. A cleaner every few months might save you an injector job later.”

“Octane boosters? Only useful if your car’s mapped for premium fuel. Otherwise, you’re paying extra for nothing.”

When to Use Fuel Additives

Here’s when adding a fuel treatment makes workshop sense:

• Your car hesitates when accelerating, idles rough, or has lost power.

• You’ve been running budget fuel for months and suspect build up.

• You’ve just bought a used car with no clear service history.

• You’re preparing a vehicle for long term storage or use in harsh weather.

Just don’t use additives as a band aid for serious engine problems. If you’ve got a misfire, a leaking injector, or failing fuel pump, no additive in the world will fix it.

The Problem with Overuse

More isn’t better. Some drivers chuck additives in every other tank, thinking they’re protecting their engine. Truth is, overuse can damage sensors, clog filters, or mess with combustion ratios.

Stick to manufacturer recommendations, usually no more than once every few thousand miles unless a trusted mechanic says otherwise.

What About Premium Fuels with Additives?

Good question. Fuels like Shell V Power or BP Ultimate already contain detergents and additives designed to keep your engine clean. So if you’re regularly fuelling up with these, additional aftermarket products are redundant for most cars.

That said, if you’re on a budget and using standard fuel, an occasional additive might bridge the gap.

Recommended Brands

Mechanics I trust have had decent results with:

• Redex: Readily available and affordable; their petrol and diesel treatments are solid all rounders.

• STP: Long time player with targeted additives like injector cleaners and fuel stabilisers.

• Liqui Moly: Premium option, especially for German cars.

• Millers Oils: UK based brand known for race quality products.

Always follow dosing instructions to the letter.

Final Thoughts

Fuel additives aren’t a scam, but they’re also not miracle workers. For well serviced cars running quality fuel, you’ll rarely need them.

For older engines, cars that sit idle, or those run hard with cheap fuel? They might just save you a trip to the garage.

The best thing you can do? Stick to a proper maintenance schedule, use good fuel, and drive smart. Fuel additives are just one small piece of the car care puzzle.

Mike Floyd

Senior Maintenance Editor, Car Care Column