Fuel Additives: The Complete Guide to Selection, Use and Comparison

Fuel additives are still a big unknown for many drivers. Some people consider them an unnecessary expense, others cannot tolerate them. The truth is, as usual, somewhere in the middle. However, a correctly chosen and regularly used additive is not a placebo, but an effective chemistry that can extend the life of the engine, reduce consumption and prevent expensive repairs. In this comprehensive guide, we look at everything you need to know to give your car the best care.

Why deal with fuel additives at all?

Think of additives as vitamins for your engine. Although basic fuels (gasoline and diesel) must meet strict standards, their quality can vary. In addition, modern engines are increasingly complex, more sensitive to fuel quality and more prone to deposit formation. Fuel additives are special chemical preparations that are added in small quantities to the tank to improve the properties of gasoline or diesel. Their main task is to keep the fuel system clean, protect it from corrosion, improve the combustion process and lubricate key engine components.

There are many types of additives, from those aimed at cleaning injectors to products for winter protection to special performance-enhancing products. The aim of this article is to guide you through the world of additives to understand how they work, what types there are and how to choose the right product for your vehicle.

Did you know that premium fuel at gas stations differs from regular fuel precisely in the quality and quantity of added additives? By adding your own additives, you can achieve similar, and sometimes better, results at a fraction of the cost.

How additives work and what happens in the engine

In order to understand the benefits of additives, it is necessary to know what is happening in the bowels of the engine and what they are actually fighting against. Their effect is based on a combination of several key components.

Detergents (cleaning ingredients)

When burning fuel, solid carbon deposits are formed. This soot gradually settles on sensitive engine parts such as injectors, intake valves, and even the pistons and combustion chamber. Clogged injectors then atomize the fuel poorly, leading to incomplete combustion, higher consumption, loss of power and higher emissions. Quality additives contain detergents (most often based on PEA – polyetheramine) which can gradually dissolve these deposits and keep the fuel system clean.

Lubricating additives

This element is critically important especially for diesel engines. Modern diesel contains very low levels of sulphur, which is good for the environment but bad for the mechanical components of the fuel system, such as the high pressure pump. Sulfur naturally provided lubricity. Additives supplement the missing lubricity of diesel fuel, thereby significantly extending the life of the injection system and protecting it from premature wear.

Corrosion inhibitors

Water can condense in the fuel system due to temperature changes. Water combined with atmospheric oxygen causes corrosion of metal parts such as the tank, fuel line or pump components. The corrosion inhibitors contained in the additives create a protective film on the metal surface that prevents contact with water and oxygen and thus protects the entire system from rust.

Burning Modifiers

These substances affect the speed and quality of the combustion of the fuel mixture. For diesel engines, these are cetane number increasers, which improve the ignitability of diesel. The result is quieter and smoother engine running, better cold starts and lower emissions. Petrol engines, on the other hand, use octane number boosters, which prevent unwanted auto-ignition (so-called engine knocking) and allow the engine to work safely under higher loads.

Types of additives: Division by fuel and purpose

The additive market is huge, so knowing exactly what you're looking for is key. Additives are divided primarily according to the type of fuel and according to their main purpose. Never confuse diesel and gasoline additives!

Diesel additives

Diesel engines are generally more sensitive to fuel quality than gasoline engines, and therefore the regular use of additives is particularly important here.

Winter Additives
An absolute must for every diesel engine driver in the winter months. Diesel solidifies at low temperatures (already around -7 °C) - so-called paraffinization occurs, when paraffin crystals are secreted from it. These crystals clog the fuel filter and make starting impossible. Winter additives contain so-called depressants that prevent the formation of these crystals and keep diesel liquid even at very low temperatures (down to -20 °C and below).

Summer additives
In the warm months there is no danger of diesel freezing, but the engine still needs care. Summer additives are mainly focused on increasing lubricity, thorough cleaning of injectors and fuel system and increasing cetane number. The result is lower consumption, quieter engine operation and protection against expensive repairs to the injection system.

Year-round (universal) additives
They represent a compromise between summer and winter variants. They contain components for cleaning and lubrication, and at the same time provide basic protection against freezing. They are ideal for drivers who want to use one product all year round and live in areas where temperatures rarely drop well below freezing.

Gasoline additives

Although gasoline engines are considered more durable, modern direct injection units are very prone to carbon build-up.

Injector cleaners and fuel systems
They are especially crucial for engines with direct injection (referred to as GDI, TSI, FSI, EcoBoost, etc.). In these engines, gasoline is injected directly into the combustion chamber and does not wash the intake valves, which suffer from the massive formation of carbon deposits. Regular use of quality cleaning additives containing PEA keeps the injectors and combustion chamber clean, ensuring optimal performance and consumption.

Octane boosters
These preparations are intended primarily for sports and high-performance cars whose engines are designed for fuels with a higher octane number (98 and more). Use in a regular car usually has no noticeable benefit. They will also be used by owners of older cars that require high-octane gasoline, which is no longer commonly available.

Gasoline stabilizers
Ideal for seasonally used vehicles such as motorbikes, vintage cars, lawnmowers or marine engines. Gasoline (especially modern with a bio-component) degrades during long-term storage, loses its properties and can form resinous deposits in the fuel system. The stabilizer slows down this aging process and keeps the fuel fresh for several months.

Special additives

Additives for cleaning DPF/FAP filters
Particulate filters (DPF) are the Achilles' heel of modern diesels, especially for frequent short-distance driving. Additives for DPF cleaning reduce the temperature required to burn soot deposited in the filter and thus support its regeneration even in city traffic. They are a great prevention against expensive filter clogging.

Additives for older engines
Veterans and older cars whose engines were designed for leaded gasoline need special care. Additives with lead replacement protect valve seats from wear.

Key parameters and composition or what to choose according to

Looking at the additive rack, it may seem like they are all the same. The opposite is true. Quality is determined by the composition and concentration of active substances.

Engine compatibility

Basic rule: always use an additive designed for your type of engine (diesel vs. gasoline). Also, check if the product is safe for your car's specific technologies, such as diesel particulate filters (DPF) or gasoline direct injection (GDI). Reputable manufacturers always include this information on the packaging.

Cetane/octane number

As already mentioned, the cetane number indicates the ignition quality of diesel, while the octane number indicates the resistance of gasoline to self-ignition. A higher cetane number in diesel means a shorter delay between injection and ignition, which results in quieter running, less smoke and better cold starts. An increase in the octane number of gasoline is mainly beneficial for powerful engines, allowing them to work more efficiently and without the risk of damage.

Lubricating additives

It is one of the most important parameters for diesel additives. Modern low-sulphur diesel without additional additives insufficiently lubricates the sensitive parts of the injection system, which leads to their faster wear. A quality additive can significantly improve lubricity and protect an investment in the order of tens of thousands of crowns.

Detergent capabilities

The ability to clean the engine is key. Look for additives that contain modern and effective detergents such as PEA (polyetheramine). This component is considered one of the most effective in removing even stubborn carbon deposits, both in gasoline and diesel engines.

Dosage

Always follow the dosage recommended by the manufacturer. The usual dilution ratio is 1:1000 (e.g. 50 ml of additive for 50 liters of fuel). Using a smaller amount will reduce the effectiveness, on the other hand, an overdose can cause problems in some cases. However, with high-quality additives, the risk of a slight overdose is minimal.

How to choose the right additive for your car

The choice depends on the condition of your vehicle, your driving style and the problem you want to solve.

For drivers with a new car

If you have a new or refurbished car, focus on prevention. By regularly using a quality year-round additive (for diesel) or a cleaner (for gasoline), you will keep the fuel system in perfect condition from the very beginning and prevent gradual engine clogging.

For owners of older cars

Older vehicles with higher mileage probably already have a significant amount of deposits in the engine. Here it is recommended to start with an intensive cleaning treatment using a more concentrated cleaning additive. After this "cure" it is ideal to switch to regular preventive dosing.

For the driver who drives short distances

Short journeys, especially in city traffic, are the biggest burden on engines. The engine does not have time to warm up properly, which leads to faster carbon formation and, in the case of diesels, to problems with the regeneration of the DPF filter. For these drivers, the regular use of cleaning additives and DPF support additives is almost a must.

When buying a used car

You never know how the previous owner took care of the car. After buying a used one, it is therefore more than advisable to thoroughly decarbonize the engine using a specialized, highly concentrated cleaning additive. This often solves problems such as irregular engine running, worse starts or increased smoke.

What to look out for when buying? Avoid suspiciously cheap products and preparations that promise instant miracles (e.g. 20% performance increase). A quality additive has its basis in chemistry, not magic.

Correct use and dosage

In order for the additive to work properly, it needs to be applied correctly.

When to apply the additive

The most important rule is: Always apply the additive to the tank BEFORE refueling. Subsequent refueling ensures perfect mixing of the additive with the entire volume of fuel. If you poured it up to a full tank, it would not disperse evenly and its effect would be limited.

How often to use

We distinguish between two basic approaches:

1. One time cleaning treatment: Used for heavily soiled engines. A higher concentration of additive is usually applied in one or two successive tanks.
2. Regular preventive use: Perfect condition. Add the recommended amount of additive each time you refuel. This keeps the engine clean and protected at all times.

Tips for safe handling

Additives are chemicals, so handle them with care. Store them out of the reach of children, in a dry and dark place. When applying, avoid contact with skin and vehicle paintwork. If you manage to splash the paint with the additive, wipe it off immediately with a cloth.

The most famous brands and manufacturers on the market

There are several proven brands on the Czech market that you can't go wrong with.

VIF

A Czech manufacturer that is the absolute leader on the domestic market. Its products, such as Super Diesel Additive or Super Benzin Additive, regularly win independent tests and offer an unrivaled price-performance ratio. It's a safe bet for regular and demanding motorists.

Liquid Moly

This German brand is synonymous with premium quality. It offers an extremely wide portfolio of products for solving specific problems – from DPF cleaning to intake channel decarbonization to special additives for LPG engines. Their products are more expensive but very effective.

STP

An American classic with a long history. The STP brand has a strong focus on cleaning and performance additives, especially for gasoline engines. Their injector cleaners are among the most popular and effective products on the market.

Millers Oils

A British premium brand with strong roots in motorsport. Their additives are often developed for maximum performance and engine protection in extreme conditions. If you are looking for uncompromising quality and performance, Millers Oils is a great choice.

Summary at the end

The rightly chosen additive is medicine for the engine, not just a placebo. It helps keep the engine in good condition, reduces the risk of expensive breakdowns and in the long term can even slightly reduce fuel consumption. The most important rule to remember is to strictly distinguish between diesel and gasoline additives, as their composition and function are completely different. When choosing, be guided primarily by the type of your engine, driving style and the purpose you want to achieve, whether it is prevention, cleaning or protection in winter. Whichever brand you choose, your engine will thank you for regular care with reliability and quieter operation.

Frequently asked questions and answers (FAQ)

Can the additive damage the engine or the DPF filter?

When using a high-quality, branded additive and observing the correct dosage, the risk of damage to the engine or its components (including the DPF) is practically zero. The problem can arise when using an inappropriate type of additive (gasoline to diesel and vice versa) or extreme overdose of low-quality products.

Does it make sense to add additives to premium fuels (Verva, V-Power)?

Yes, although to a lesser extent. Premium fuels already contain a superior package of additives from the factory. However, by adding another high-quality additive, you can strengthen their effects even more, especially in terms of lubricity for diesel or cleaning capabilities. Many drivers apply half the additive dose even in premium fuels for maximum protection.

Do I notice a difference in the engine immediately after the first application?

An immediate and pronounced effect is rather exceptional, usually in very neglected engines. Typically, the effects occur gradually. You can notice an improvement in cold starts or quieter running of the diesel engine already after the first tank. However, the full cleaning effect will only become apparent after burning several tanks with the additive, when older deposits are gradually removed. The key to success is patience and regularity.