AMSOIL Fuel Additives Explained: Which One Should You Use?

AMSOIL offers a wide range of petrol and diesel fuel additives, but they are not all designed to do the same job. Some are concentrated cleaners, some are intended for regular use, some improve fuel ignition quality and others solve specific problems such as fuel storage, cold-weather operation or insufficient octane.

That can make choosing the right bottle surprisingly confusing. Do you need P.i. Performance Improver or Upper Cylinder Lubricant? What is the difference between Diesel Injector Clean, Cetane Boost and Diesel All-In-One? And where do products such as Quickshot, Gasoline Stabilizer and DOMINATOR Octane Boost fit?

This guide explains what each AMSOIL fuel additive is designed to do, where the products overlap and which one makes the most sense for the problem you are trying to solve.

Start With the Problem You Are Trying to Solve

The easiest way to understand fuel additives is to stop thinking of them as one product category and instead consider the job each additive is intended to perform.

A fuel-system cleaner is different from an octane booster. A regular-use petrol additive is different from a concentrated deposit-removal treatment. Likewise, a diesel additive designed to clean injectors is not necessarily the same product you would choose to improve cetane or prevent fuel gelling in very cold weather.

Choosing the correct additive therefore starts with a simple question: what are you trying to achieve?

AMSOIL Petrol Fuel Additives

AMSOIL petrol additives cover several different applications, including intensive fuel-system cleaning, regular-use maintenance, fuel storage, powersports equipment and octane improvement.

P.i. Performance Improver: Deep Fuel-System Cleaning

AMSOIL P.i. Performance Improver is the concentrated cleaning option in the petrol range. It is designed to attack stubborn deposits in fuel injectors, intake valves and combustion chambers and is suitable for both port-injected and gasoline direct-injection engines.

Rather than being intended as an additive for every tank, P.i. is best thought of as a periodic deep-clean treatment. AMSOIL recommends treating the fuel system periodically to help control deposit accumulation and maintain performance.

AMSOIL testing has shown P.i. can restore heavily fouled GDI injector flow and help recover performance lost to deposits. In one third-party test using a high-mileage 2016 Chevrolet Silverado, one treated tank was associated with an improvement of up to 14% in measured horsepower. Results will naturally vary depending on the vehicle and the amount of existing deposit build-up.

Choose P.i. when: you want an intensive petrol fuel-system clean, particularly where deposits may be contributing to rough running, reduced performance or injector fouling.

Upper Cylinder Lubricant: Regular-Use Protection

AMSOIL Upper Cylinder Lubricant serves a different purpose. Rather than acting primarily as an aggressive clean-up treatment, it is designed for regular use to help maintain injector cleanliness while adding lubricity and corrosion protection to the fuel system and upper-cylinder area.

It is particularly useful where the aim is to maintain cleanliness after deposits have already been removed. AMSOIL positions Upper Cylinder Lubricant as a product that can be used regularly to help preserve fuel-system cleanliness and provide additional lubrication to fuel-system and upper-cylinder components.

Its formulation also provides corrosion protection for fuel-system components, including applications using ethanol-blended petrol.

Choose Upper Cylinder Lubricant when: you want an ongoing petrol treatment focused on cleanliness, lubricity and corrosion protection rather than a one-off intensive clean.

P.i. vs Upper Cylinder Lubricant

P.i. and Upper Cylinder Lubricant are sometimes viewed as competing products, but they are better understood as complementary treatments.

P.i. is the deep cleaner. It is designed to remove stubborn deposits that have already accumulated.

Upper Cylinder Lubricant is the maintenance product. It helps preserve cleanliness while providing additional lubricity and corrosion protection during regular use.

A simple way to think about the pair is: P.i. cleans it up; Upper Cylinder Lubricant helps keep it clean.

Gasoline Additive: Regular Fuel-System Cleanliness

AMSOIL Gasoline Additive is another regular-use petrol treatment designed to help control fuel-injector, intake-valve and combustion-chamber deposits.

It sits between the aggressive periodic cleaning approach of P.i. and the lubricity-focused role of Upper Cylinder Lubricant. It provides a convenient treatment for drivers who primarily want to help prevent deposit accumulation and maintain fuel-system cleanliness.

Choose Gasoline Additive when: you want a straightforward regular-use petrol treatment focused primarily on deposit control.

Quickshot: Motorcycles, Small Engines & Powersports

AMSOIL Quickshot is designed specifically for motorcycles, small engines and powersports equipment, where fuel can spend long periods sitting in tanks, carburettors and fuel systems between uses.

These applications can be particularly vulnerable to degraded petrol, varnish, gum, water contamination and ethanol-related fuel problems. Quickshot is formulated to clean fuel systems while also helping stabilise fuel during short-term storage.

That makes it especially well suited to equipment such as motorcycles, lawn equipment, generators, boats, ATVs and other petrol-powered machines that may not be used every day.

Choose Quickshot when: you are treating a motorcycle, powersports vehicle or small engine where fuel cleanliness, ethanol-related issues and short-term storage are concerns.

Gasoline Stabilizer: Long-Term Petrol Storage

AMSOIL Gasoline Stabilizer is the dedicated storage product in the petrol range.

Petrol can deteriorate during storage, leading to oxidation, gum and varnish formation that can contribute to blocked carburettors, injectors and fuel passages. Gasoline Stabilizer is designed to slow this deterioration and help keep stored fuel usable.

It is particularly useful for vehicles and equipment that may sit unused for extended periods, including classic cars, motorcycles, marine equipment, generators and seasonal machinery.

Choose Gasoline Stabilizer when: the primary concern is protecting petrol during extended storage rather than cleaning an engine that is regularly operated.

DOMINATOR Octane Boost: Increasing Petrol Octane

AMSOIL DOMINATOR Octane Boost has a completely different purpose from the cleaners and maintenance additives above. It is designed to increase petrol octane and is aimed primarily at performance applications where additional knock resistance is required.

AMSOIL states that DOMINATOR Octane Boost can increase octane by up to four numbers when used at the recommended treatment rate. It is also marketed for use as a lead substitute in compatible older or collector vehicles.

It should not be confused with a fuel-system cleaner. If the problem is dirty injectors or deposits, P.i. or another cleaning additive is the more appropriate starting point.

Choose DOMINATOR Octane Boost when: the objective is to increase the fuel's resistance to knock in a compatible high-performance application.

AMSOIL Diesel Fuel Additives

Diesel fuel additives cover an even broader range of problems. Modern high-pressure common-rail fuel systems require extremely precise injector operation, while diesel fuel quality can also affect lubricity, cetane, cold-weather performance, corrosion and deposit formation.

Diesel Injector Clean: Concentrated Injector Cleaning

AMSOIL Diesel Injector Clean is the cleaning-focused option in the diesel range. It is formulated to target deposits in both traditional diesel injectors and modern high-pressure common-rail systems.

Injector deposits can interfere with the extremely small clearances and precise operation found in modern diesel injection systems, potentially affecting spray pattern, combustion quality, power and drivability.

Diesel Injector Clean also adds lubricity and corrosion protection, but its primary distinction is strong injector and fuel-system cleaning without the added cetane emphasis of some other products.

Choose Diesel Injector Clean when: your main priority is cleaning dirty diesel injectors and maintaining fuel-system cleanliness.

Diesel Injector Clean + Cetane Boost: Cleaning Plus Ignition Quality

AMSOIL Diesel Injector Clean + Cetane Boost combines strong injector-cleaning performance with an increase in cetane.

This makes it a useful option where both injector cleanliness and fuel ignition quality are priorities. AMSOIL states that it can increase cetane by up to eight points while also providing detergency, lubricity and corrosion protection.

If you are already considering Diesel Injector Clean but would also like the benefits of increased cetane, this is the more comprehensive option.

Choose Diesel Injector Clean + Cetane Boost when: you want concentrated injector cleaning and a significant cetane increase from the same treatment.

Diesel Cetane Boost: Improve Diesel Ignition Quality

AMSOIL Diesel Cetane Boost is focused primarily on increasing the cetane number of diesel fuel.

Cetane describes how readily diesel fuel ignites after injection. Fuel with suitable cetane characteristics can support easier starting, smoother combustion and better engine response.

AMSOIL Diesel Cetane Boost is designed to raise cetane by up to eight points, making it the most direct choice when fuel ignition quality is the main concern rather than injector cleaning or cold-weather protection.

Choose Diesel Cetane Boost when: you primarily want to improve diesel fuel ignition quality and cetane number.

Diesel All-In-One: The Broad-Spectrum Diesel Treatment

AMSOIL Diesel All-In-One combines several different diesel-fuel treatments into one product.

It provides injector cleaning, increased lubricity, corrosion protection and a cetane increase while also including cold-flow protection for low-temperature operation. It is the convenient option for users who want broad diesel-fuel treatment without purchasing several separate additives.

It is particularly useful as an ongoing general-purpose diesel additive where cleaning, lubrication, cetane and fuel-condition protection are all desirable.

Choose Diesel All-In-One when: you want one product that addresses several common diesel-fuel concerns at the same time.

Diesel Cold Flow: Preventing Fuel Gelling

AMSOIL Diesel Cold Flow is a preventative cold-weather treatment designed to improve the flow characteristics of diesel fuel as temperatures fall.

Diesel contains naturally occurring waxes that can crystallise in sufficiently cold conditions. As these crystals grow, they can restrict or block fuel filters and eventually prevent fuel from reaching the engine.

Diesel Cold Flow is designed to be added before this gelling occurs. It is therefore a preventative product rather than a cure for fuel that has already gelled.

For most Australian road vehicles this will be a specialised requirement, but it can be relevant to vehicles and equipment operating in alpine or particularly cold environments.

Choose Diesel Cold Flow when: you need preventative protection against diesel waxing and filter plugging in very cold conditions.

Diesel Recovery: When the Fuel Has Already Gelled

AMSOIL Diesel Recovery is an emergency treatment rather than an everyday diesel additive.

It is designed to dissolve wax crystals after diesel fuel has already gelled and can also be used to help thaw a wax-blocked fuel filter.

The distinction between Diesel Cold Flow and Diesel Recovery is therefore simple: Cold Flow helps prevent the problem; Diesel Recovery is intended to deal with the problem after it has occurred.

Choose Diesel Recovery when: diesel fuel has already gelled or wax has blocked the fuel system in extreme cold.

Which AMSOIL Fuel Additive Should You Use?

Can You Use More Than One Fuel Additive?

Some AMSOIL fuel additives perform complementary jobs, so there are situations where more than one product can form part of a maintenance routine.

P.i. and Upper Cylinder Lubricant are a good example. P.i. can be used periodically for intensive deposit removal, while Upper Cylinder Lubricant can be used regularly between treatments to help maintain cleanliness and provide additional lubricity.

Likewise, specialised diesel products can address different fuel characteristics. However, there is no advantage in adding multiple products simply because they are available. Diesel All-In-One already combines several functions that would otherwise require separate treatments.

Always follow the treatment instructions for the product being used and avoid exceeding the recommended concentration.

Fuel Additives Cannot Fix Mechanical Problems

Fuel additives can help control deposits, improve certain fuel properties and address problems associated with fuel quality, but they are not a substitute for diagnosing a mechanical or electrical fault.

A vehicle with a failed injector, low fuel pressure, ignition fault, compression problem, damaged sensor or other mechanical issue will not be repaired simply by pouring an additive into the tank.

Where a vehicle has persistent starting problems, severe misfires, warning lights or significant loss of performance, the underlying fault should be diagnosed rather than assuming contaminated fuel or deposits are the only possible cause.

The Bottom Line

There is no single "best" AMSOIL fuel additive because the products are designed to solve different problems.

For petrol vehicles, P.i. Performance Improver is the intensive cleaner, Upper Cylinder Lubricant is the ongoing lubricity and maintenance treatment, Gasoline Additive provides convenient regular deposit control, Quickshot targets powersports and small-engine fuel systems, Gasoline Stabilizer protects stored petrol and DOMINATOR Octane Boost is intended to increase octane.

For diesel engines, Diesel Injector Clean focuses on cleaning, Diesel Cetane Boost focuses on ignition quality, Diesel Injector Clean + Cetane Boost combines the two and Diesel All-In-One provides the broadest all-round treatment. Diesel Cold Flow and Diesel Recovery handle the specialised problem of diesel waxing in extreme cold.

Rather than choosing an additive based on which bottle sounds the most powerful, start by identifying the result you actually need. Once that is clear, the AMSOIL fuel-additive range becomes much easier to understand.