Best Engine Additive (2026): 4 Additives Compared
Engine additives compared by type, size, dosing and stated claims: a gasoline fuel cleaner, an oil friction reducer and title-only oil treatments.
On this page
Top picks at a glance
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- 1
Best Fuel System CleanerHot Shot’s GE12Z9.6/10View on Amazon - 2
Best Oil AdditiveHot Shot’s FR39.6/10View on Amazon - 3
Prolube 16 ozProlube 16 oz9.4/10View on Amazon - 4
Prolube 1 QTProlube 1 QT9.5/10View on Amazon - 5
STA-BIL Small Engine Pro Multi-System AdditiveView on Amazon - 6
VP Racing Octane Booster Unleaded Gasoline Additive 473 mlView on Amazon - 7
Design Engineering Radiator Relief Coolant Additive 16 ozView on Amazon
During an oil change, with the drain plug back in and fresh oil going in, the question comes up naturally: is there an additive worth adding while you are already under the hood? This roundup compares the best engine additive listings for fuel systems and oil, so you can match the bottle to the job instead of guessing at the shelf.
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Quick picks
- Best Fuel System Cleaner Hot Shot’s GE12Z: 12 oz treats 20 gallons, cleans injectors and fuel system Check price on Amazon
- Best Oil Additive Hot Shot’s FR3: 8 oz treats 5 quarts, for gas and diesel engines Check price on Amazon
- Prolube 16 oz Prolube 16 oz: Oil treatment for gas and diesel engines, 16 oz bottle Check price on Amazon
- Prolube 1 QT Prolube 1 QT: Oil treatment for gas and diesel engines, 1 QT bottle Check price on Amazon
Picks for the garage
Hot Shot's Secret Gasoline Extreme Fuel Additive
A gasoline fuel system cleaner that pours into the tank to clean injectors and restore performance.
Pros
- Cleans valves, pumps, injectors, rings, pistons and upper cylinders per the listing
- Stated dose of 12 oz for every 20 gallons of gasoline
- Maker claims fuel economy gains of up to 7.9%
- P.E.A. technology stated for dissolving gum and varnish
Cons
- No safety certification is stated on the listing
- No warranty term with a time limit is stated
- Fuel system cleaner only, not an oil additive
- Dosing repeats at fill up or every 10,000 miles
Hot Shot's Secret FR3 Friction Reducer Oil
A synthetic oil additive for gas and diesel engines that doses per quart to reduce friction and noise.
Pros
- For gas and diesel engines, with synthetic and conventional oil
- Stated dose of 1.5 oz per quart, treating 5 quarts
- Maker claims reduced lifter and valve noise and restored compression
- Maker claims horsepower and fuel economy gains of up to 5 percent
Cons
- Must not be combined with Stiction Eliminator or other aftermarket oil additives
- No safety certification is stated on the listing
- No warranty term with a time limit is stated
- Displaces the same amount of oil, so measure before pouring
Prolube Oil Treatment - Engine Oil Additive
A 32 fl oz oil treatment for gas and diesel engines and transmissions, with maker claims of reduced wear, noise and vibration and improved fuel economy.
Pros
- Stated for gas and diesel engines, plus transmissions
- Clear mixing ratios: 1 oz per quart standard, 2 oz per quart heavy-duty
- Maker claims wear reduced by up to 45 percent
- Blends with synthetic and conventional oils, per the listing
Cons
- No warranty term is stated
- Horsepower and fuel economy gains are maker claims, not stated results
- No weight is stated in the listing
- No flash point or temperature limit is stated
Prolube Oil Treatment - Engine Oil Additive
A 16 fl oz oil treatment for gas and diesel engines, transmissions and differentials, with 1 oz per quart for standard engines and 2 oz per quart for heavy-duty or high-mileage engines, and a claim of wear reduced by up to 45%.
Pros
- Claims wear reduced by up to 45%
- Works on gas and diesel engines, transmissions and differentials
- Blends with synthetic and conventional oils
- Clear mixing ratios for standard and heavy-duty engines
Cons
- No warranty term is stated
- No stiction claim is stated
- No fuel system product is included
- 16 fl oz bottle is smaller than the 64 oz and 128 Fluid Ounce picks
Other tools worth a look
STA-BIL Small Engine Pro Multi-System AdditiveCheck price on Amazon
VP Racing Octane Booster Unleaded Gasoline Additive 473 mlCheck price on Amazon
Design Engineering Radiator Relief Coolant Additive 16 ozCheck price on Amazon
Compared on paper
| Additive | Shop Score | Type | Size | Treats | Use |
|---|---|---|---|---|---|
| Hot Shot’s GE12Z | 9.6/10 | Fuel additive | 12 oz | 20 gallons | Gasoline engines |
| Hot Shot’s FR3 | 9.6/10 | Oil additive | 8 oz | 5 quarts | Gas and diesel engines |
| Prolube 16 oz | 9.4/10 | Oil treatment | 16 oz | Not stated | Gas and diesel engines |
| Prolube 1 QT | 9.5/10 | Oil treatment | 1 QT | Not stated | Gas and diesel engines |
Specifications are manufacturer rated, as published on each listing and collected 2 November 2026.
How the points were given
Each additive is scored on performance, build, value, safety and warranty, with the weights published on our How We Pick page. None of the listings here states a safety certification, and none states a warranty term with a time limit, so safety and warranty score zero across the list. The two title-only listings score below the two full listings because their pages state no bullets, specs or dosing.
| Product | Shop Score | Perf. /35 | Build /25 | Value /25 | Safety /10 | Warranty /5 |
|---|---|---|---|---|---|---|
| Hot Shot’s GE12Z | 9.6 | 30 | 21 | 21 | n/a | 0 |
| Hot Shot’s FR3 | 9.6 | 29 | 21 | 20 | n/a | 0 |
Scores run from 9.2 to 9.8: each product’s point total is placed on that range, so more points always means a higher score. Safety counts only for powered gear or where the listing states safety features; where it does not apply, the score is taken over the remaining 90 points.
What the listings tell you
The listings split cleanly into two kinds. Hot Shot’s Secret gives full pages: a fuel system cleaner with a stated dose and interval, and an oil additive with a stated dose per quart, while Prolube gives title-only pages that name the job and the bottle size and nothing else. Every performance claim here is a maker claim, from fuel economy gains to restored compression, and the listings state no independent verification. Read the dose and the stated engine types before buying, since the fuel cleaner goes in the tank and the oil treatments go in the oil.
How to choose the best engine additive
Fuel additive or oil additive
Start with where the bottle goes. Gasoline Extreme pours into the fuel tank at 12 oz for every 20 gallons of gasoline, and its listing pitches cleaning for valves, pumps, injectors, rings, pistons and upper cylinders. FR3 and the Prolube pair are oil treatments: FR3 doses at 1.5 oz per quart of oil for gas and diesel engines, while the Prolube titles name gas and diesel engines plus transmissions and differentials. For more oil options, see our best engine oil additive roundup, and for diesel fuel options, see our best diesel fuel additive picks.
Dosing and intervals
Dosing is the clearest difference between the full listings and the title-only pair. Gasoline Extreme states 12 oz per 20 gallons, applied at fill up or every 10,000 miles, while FR3 states 1.5 oz per quart and treats 5 quarts from an 8 oz bottle, displacing the same amount of oil. The Prolube titles state no dose at all, only bottle sizes of 16 oz and 1 QT, so a buyer must guess at the pour. FR3 also states a restriction: do not use it in combination with Stiction Eliminator or other aftermarket oil additives.
What the title-only listings leave out
A title-only page leaves every practical question open. The Prolube titles state the scope, gas and diesel engines, transmissions and differentials, plus wear, noise and vibration claims, but they state no bullets, no specs, no dosing and no warranty term. That does not make them wrong, but it does make them a weaker buy than a listing that states its dose, its interval and its limits. If the title scope is exactly your job, they still deserve a look; if you want dosing guidance, pick a full listing.
Use rated jack stands on solid ground, wear eye protection with power and air tools, keep fuel-burning equipment out of a closed garage, and follow the manual for every tool. Read our Safety Disclaimer.
Garage Fit Check
- Check the dose before pouring: 12 oz per 20 gallons for the fuel cleaner, 1.5 oz per quart for FR3.
- Check compatibility: FR3 states gas and diesel engines with synthetic and conventional oil, while the Prolube titles name gas and diesel engines.
- Check the warranty field before buying: neither Hot Shot’s listing states a warranty term with a time limit.
- Do not mix FR3 with Stiction Eliminator or other aftermarket oil additives, per the FR3 listing.
FAQ: garage tools
What are oil additives?
Oil additives are liquids poured into engine oil, and the listings here claim they reduce friction and wear, quiet lifter and valve noise, and restore lost compression. FR3 doses at 1.5 oz per quart of oil.
Are oil additives good for an engine?
The listings claim reduced friction and wear and smoother operation, but those are maker claims and no listing here states independent verification. Match the stated engine types and dose to your own vehicle before deciding.
What is the difference between a fuel additive and an oil additive?
A fuel additive goes in the tank, like Gasoline Extreme at 12 oz per 20 gallons, while an oil additive goes in the oil, like FR3 at 1.5 oz per quart. They serve different systems, so the bottle must match the job.
How often do you use a fuel additive?
The Gasoline Extreme listing states application at fill up or every 10,000 miles, in a single treatment per dose.
What is the best engine oil additive to stop smoke?
None of the listings here states a smoke claim, so pick by the stated claims instead: fuel system cleaning, friction reduction, or the oil treatment scope in the Prolube titles.
Related: the engine and shop equipment guides. Also see our best engine oil additive. Also see our best diesel fuel additive. Also see our best oil additive for diesel. Also see our best engine oil additive for high mileage.
