When Should Fuel Additives Be Added to Petrol Vehicles

From a mechanic’s perspective: fuel additives are a quick fix, not a cure-all. Use them sparingly—only when symptoms like rough idling or reduced MPG appear. For example, a Vauxhall Corsa with sticky valves might benefit from a decarbonising treatment. Avoid cheap, untested products; stick to reputable brands like BG or Liqui Moly. Regular servicing is far more effective than relying on additives.

Additionally, the use of fuel additives depends on the vehicle's operating environment. For instance, vehicles frequently driven in urban areas are more prone to carbon buildup and thus require regular use of fuel additives. Secondly, it is essential to use fuel additives before long-distance journeys, as petrol quality can vary across different regions, potentially causing issues. Using fuel additives serves as a protective measure.

Purchasing legitimate petrol additives generally ensures quality and provides certain benefits for your vehicle. Counterfeit or substandard petrol additives not only fail to save fuel but may also have adverse effects. Adulterated petrol additives often contain excessive impurities or are simply diluted with water. Adding such products to your vehicle can cause severe damage to the engine. Do not blindly trust products promoted by petrol station attendants; instead, opt for those from manufacturers with proper certifications or third-party on-site accreditation.

There are two types of petrol additives: cleaning and cleansing. Cleaning: The primary function is to clean the fuel system and remove carbon deposits. Typically, this type of additive should be used in a course (three bottles) every 5,000-8,000 kilometres. Of course, the first application requires a larger quantity for thorough cleaning. Cleansing: Its main purpose is to purify the fuel and reduce emissions. If possible, use one bottle per tank or every other tank. As a petrol additive, it is introduced into the fuel tank during refuelling. This is the basic method of using petrol additives. For engine oil additives, they are added alongside the oil.

Fuel tank

Engine oil

Before adding the additive, check the fuel level in the tank and wait until refuelling is needed. Drive the vehicle to a petrol station, park next to the pump, open the petrol cap, and remove the seal from the fuel additive bottle using the sharp edge of the cap. Pour the entire contents of the opened bottle directly into the petrol tank. The petrol station attendant can then begin refuelling to fill the tank, allowing the force of the petrol to disperse the additive and ensure complete mixing with the fuel.

Fuel additives should be added to petrol vehicles when addressing specific issues or maintaining engine performance. Common scenarios include improving fuel efficiency, cleaning injectors, preventing carbon deposits, or protecting against corrosion. For optimal results, follow these guidelines:

1. Preventative maintenance: Add a fuel system cleaner every 3,000-5,000 miles to prevent carbon buildup. Products like Redex or STP can help maintain injector performance.
2. Poor performance: If the engine feels sluggish or fuel economy drops, a cleaner may restore efficiency by removing deposits.
3. Older vehicles: High-mileage engines benefit from additives that reduce wear and seal minor leaks.
4. Ethanol-blended fuel: Additives can counteract moisture absorption, which is common with E10 petrol.

Avoid overuse—excessive additives can harm sensors or catalytic converters. Always check the manufacturer’s recommendations, as some modern engines (e.g., direct-injection turbos in a Ford Focus ST) may require specific formulations.