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The best fuel stabilizer and cleaner keeps fuel fresh in storage and cleans the fuel system while the engine runs, so a generator that sits for months still starts when you need it. The four additives here cover both jobs in different ways: two state stabilizer claims, one states a full system clean, and two state measured economy and horsepower figures. The Royal Purple case leads the scoring on stated figures; the Red Line follows with the widest cleaning claims; and the STA-BIL is the only one that states a storage period.
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Quick picks
Best Overall Royal Purple Max-Clean 6PK: 3-in-1 with 3.2 percent economy and 2.6 percent horsepower figures stated Check price on Amazon
Best Stabilizer STA-BIL 360 Protection: Keeps ethanol-blended fuels fresh for up to 12 months Check price on Amazon
Best System Cleaner Red Line SI-1: Cleans injectors, carburetors, valve and combustion chamber deposits Check price on Amazon
2-Pack Pick Royal Purple Max-Clean 2PK: Same 3.2 percent economy claim in a 2-pack Check price on Amazon
The kits we chose
| # | Product | Solar Score | Buy |
|---|---|---|---|
| 1 | Royal Purple Max-Clean 6PK | 9.6/10 | Buy on Amazon |
| 2 | Red Line SI-1 | 9.6/10 | Buy on Amazon |
| 3 | STA-BIL 360 Protection | 9.6/10 | Buy on Amazon |
| 4 | Royal Purple Max-Clean 2PK | 9.6/10 | Buy on Amazon |
Royal Purple Max-Clean 6PK
A 3-in-1 fuel system cleaner and stabilizer in a case of 6 bottles of 20 oz, with stated economy, horsepower and emissions figures.
Pros
- 3-in-1 cleaner and stabilizer stated
- Fuel economy up an average of 3.2 percent stated
- Horsepower up an average of 2.6 percent stated
- Hydrocarbon, NOx and CO emissions down 12, 13 and 18 percent on average stated
Cons
- No warranty term stated
- No dose stated
- No storage period stated
Detailed Review
The listing states a 3-in-1 fuel additive in a case of 6 bottles of 20 oz that keeps new engines clean and improves performance. It states fuel economy up by an average of 3.2 percent, horsepower up by an average of 2.6 percent, and hydrocarbon, NOx and CO emissions down by 12, 13 and 18 percent on average. It states it prevents rough idle, hesitation and stalling. The spec table lists 5.5 by 8.25 by 9.0 inches.
Who it's for: owners who want stated figures for economy, horsepower and emissions in a case of 6. Who should skip it: anyone who wants a stated storage period, which this listing does not give.
Its Solar Score of 9.6/10 comes from performance 32/35, build 21/25, value 21/25, safety 5/10 and warranty 0/5: 79 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Size | 20 oz, case of 6 |
|---|---|
| Type | 3-in-1 cleaner and stabilizer |
| Economy | 3.2 percent average |
| Horsepower | 2.6 percent average |
| Emissions | 12, 13 and 18 percent down on average |
| Dimensions | 5.5 x 8.25 x 9.0 in |
Figures as published on the retailer listing, collected 10 November 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. Prevents rough idle, hesitation and stalling stated, so safety scores 5 of 10. No warranty term, so warranty scores zero. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
Red Line SI-1
A complete fuel system cleaner in a 2-pack of 15 oz bottles that cleans injectors, carburetors, valve and combustion chamber deposits and prevents corrosion.
Pros
- Cleans injectors, carburetors, valve and combustion chamber deposits stated
- Prevents corrosion in fuel systems stated
- Nearly 100 percent efficiency in one treatment stated
- 2-pack of 15 oz bottles
Cons
- No warranty term stated
- No storage period stated
- No economy or horsepower figure stated
- No ethanol protection line stated
Detailed Review
The listing states a complete SI-1 fuel system cleaner in a 2-pack of 15 oz bottles that cleans injectors, carburetors, valve and combustion chamber deposits with high-temp and low-temp detergents. It states the additive cleans nearly 100 percent efficiency in one treatment, enhances gasoline stability, reduces gum and varnish formation, and prevents corrosion in fuel systems. One bottle per tank is stated for most effective treatment.
Who it's for: owners who want the widest cleaning claims here, across injectors, carburetors, valve and combustion chamber. Who should skip it: anyone who wants a stated storage period, which this listing does not give.
Its Solar Score of 9.6/10 comes from performance 30/35, build 20/25, value 21/25, safety 5/10 and warranty 0/5: 76 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Size | 15 oz, pack of 2 |
|---|---|
| Type | Complete fuel system cleaner |
| Dose | 1 bottle per tank |
| Cleans | Injectors, carburetors, valve, combustion chamber |
| Stability | Gasoline stability stated |
Figures as published on the retailer listing, collected 10 November 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. Prevents corrosion in fuel systems stated, so safety scores 5 of 10. No warranty term, so warranty scores zero. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
STA-BIL 360 Protection
A fuel system treatment and injector cleaner in a 4 oz bottle that treats 5 gallons and keeps ethanol-blended fuels fresh for up to 12 months.
Pros
- Treats 5 gallons per 4 oz bottle stated
- Keeps ethanol-blended fuels fresh for up to 12 months stated
- Removes water, gum and varnish stated
- Protects against corrosion and ethanol damage stated
Cons
- No warranty term stated
- No economy figure stated, only an MPG booster line
- 4 oz bottle, the smallest here
- No horsepower figure stated
Detailed Review
The listing states a fuel system treatment and injector cleaner in a 4 oz bottle that treats 5 gallons. It states the additive cleans fuel injectors and fuel pumps, removes water, gum and varnish, and protects against corrosion and ethanol damage. It states ethanol-blended fuels stay fresh for up to 12 months, with one 4 oz bottle for every 5 gallons of fuel and the engine run for 5 minutes to treat the system. All STA-BIL branded products are good for use up to 2 years after the bottle was opened, per the listing.
Who it's for: owners who store ethanol-blended fuel and want a stated 12-month fresh period with a clear dose. Who should skip it: anyone who wants stated economy or horsepower figures, which this listing does not give.
Its Solar Score of 9.6/10 comes from performance 29/35, build 20/25, value 21/25, safety 6/10 and warranty 0/5: 76 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Size | 4 oz |
|---|---|
| Treats | 5 gallons per bottle |
| Storage | Fresh up to 12 months |
| Use after opening | Up to 2 years |
| Dimensions | 1.6 x 2.6 x 0.5 in |
Figures as published on the retailer listing, collected 10 November 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. Protects against corrosion and ethanol damage stated, so safety scores 6 of 10. No warranty term, so warranty scores zero. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
Royal Purple Max-Clean 2PK
A 3-in-1 fuel system cleaner and stabilizer in a 2-pack of 20 oz bottles, with stated economy and horsepower figures.
Pros
- 3-in-1 cleaner and stabilizer stated
- Fuel economy up an average of 3.2 percent stated
- Horsepower up an average of 2.6 percent stated
- 1.25 pounds at 4.0 by 6.0 by 10.0 inches stated
Cons
- No warranty term stated
- No dose stated
- No storage period stated
Detailed Review
The listing states a 3-in-1 fuel additive in a 2-pack of 20 oz bottles that keeps new engines clean and improves performance. It states fuel economy up by an average of 3.2 percent and horsepower up by an average of 2.6 percent. The spec table lists 1.25 pounds at 4.0 by 6.0 by 10.0 inches, and NumberOfItems 1 for a pack of 2.
Who it's for: owners who want the same 3-in-1 claims as the 6-pack in a smaller pack. Who should skip it: anyone who wants a stated storage period, which this listing does not give.
Its Solar Score of 9.6/10 comes from performance 29/35, build 20/25, value 21/25, safety 5/10 and warranty 0/5: 75 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Size | 20 oz, pack of 2 |
|---|---|
| Type | 3-in-1 cleaner and stabilizer |
| Economy | 3.2 percent average |
| Horsepower | 2.6 percent average |
| Weight | 1.25 lb |
| Dimensions | 4.0 x 6.0 x 10.0 in |
Figures as published on the retailer listing, collected 10 November 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. 3-in-1 cleaner and stabilizer stated, so safety scores 5 of 10. No warranty term, so warranty scores zero. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
As an Amazon Associate I earn from qualifying purchases.
Numbers side by side
| Fuel stabilizer | Solar Score | Size | Treats | Stabilizer stated | Economy claim | Amazon |
|---|---|---|---|---|---|---|
| Royal Purple Max-Clean 6PK | 9.6/10 | 20 oz, case of 6 | Not stated | Stabilizer stated | 3.2 percent average | View on Amazon |
| Red Line SI-1 | 9.6/10 | 15 oz, 2-pack | 1 bottle per tank | Stability stated | Not stated | View on Amazon |
| STA-BIL 360 Protection | 9.6/10 | 4 oz | 5 gallons per bottle | Fresh up to 12 months | MPG booster stated | View on Amazon |
| Royal Purple Max-Clean 2PK | 9.6/10 | 20 oz, pack of 2 | Not stated | Stabilizer stated | 3.2 percent average | View on Amazon |
All numbers here are manufacturer claims from the listings, not our measurements (10 November 2026).
Where the points went
The Solar Score weighs performance, build, value, safety and warranty. For a fuel additive, safety means corrosion prevention, ethanol damage protection or another protection the listing actually states; a listing that states none scores low on that line. None of the four listings states a warranty term, which is why the warranty line scores zero across the group. How we pick explains the weights.
| Product | Solar Score | Perf. /35 | Build /25 | Value /25 | Safety /10 | Warranty /5 |
|---|---|---|---|---|---|---|
| Royal Purple Max-Clean 6PK | 9.6 | 32 | 21 | 21 | 5 | 0 |
| Red Line SI-1 | 9.6 | 30 | 20 | 21 | 5 | 0 |
| STA-BIL 360 Protection | 9.6 | 29 | 20 | 21 | 6 | 0 |
| Royal Purple Max-Clean 2PK | 9.6 | 29 | 20 | 21 | 5 | 0 |
Scores start at 9.2 for the lowest totals and top out at 9.8. In between, a kit’s position follows its weighted points one to one in order.
How to choose the best fuel stabilizer and cleaner
Start from the job: clean or stabilize
Two of the four listings state stabilizer in the name: both Royal Purple bottles are a cleaner and stabilizer, and the STA-BIL is a fuel system treatment and injector cleaner that also stabilizes. The Red Line states it enhances gasoline stability while it cleans. If the fuel sits for months, the stabilizer claim matters; if the engine already runs rough, the cleaning claims matter more.
Read the stated figures
Only the two Royal Purple listings state measured figures: fuel economy up by an average of 3.2 percent, horsepower up by an average of 2.6 percent, and hydrocarbon, NOx and CO emissions down by 12, 13 and 18 percent on average. The Red Line states nearly 100 percent efficiency in one treatment, and the STA-BIL states no economy figure at all, only an MPG booster line. Compare the measured figures, not the adjectives.
Dose and storage
The STA-BIL states one 4 oz bottle for every 5 gallons of fuel, with the engine run for 5 minutes to treat the system, and fuel kept fresh for up to 12 months. The Red Line states one bottle per tank. Both Royal Purple listings state 20 oz bottles with no dose stated. All STA-BIL branded products are good for use up to 2 years after the bottle was opened, per the listing.
Read the warranty lines closely
None of the four listings states a warranty term, so the warranty line scores zero across the group. The STA-BIL listing states its products are good for use up to 2 years after the bottle was opened, which is a shelf-life line, not a warranty term. The other three list no warranty line at all.
| If you need | Look at |
|---|---|
| Widest cleaning claims | Red Line SI-1, injectors, carburetors, valve and combustion chamber |
| Longest stated storage | STA-BIL 360 Protection, fresh up to 12 months |
| Stated economy figures | Royal Purple Max-Clean 6PK, 3.2 percent average |
| Smallest stated dose | STA-BIL 360 Protection, 4 oz per 5 gallons |
Sizing Notes
- Match the additive to your fuel: the listings here are gasoline treatments, and the STA-BIL names ethanol-blended fuels.
- Dose per the listing: one 4 oz STA-BIL bottle for every 5 gallons, or one Red Line bottle per tank.
- Run the engine for 5 minutes after adding the STA-BIL, per the listing, to treat the system.
- Store fuel per the listing: the STA-BIL keeps ethanol-blended fuels fresh for up to 12 months.
FAQ: power away from the grid
What does a fuel stabilizer do?
It keeps fuel fresh in storage. The STA-BIL listing states it keeps ethanol-blended fuels fresh for up to 12 months, and the Red Line listing states it enhances gasoline stability while reducing gum and varnish formation.
How much STA-BIL treats 5 gallons?
One 4 oz bottle, per the listing. Pour it into the tank before fill up, then run the engine for 5 minutes to treat the system.
Which additive here states economy figures?
Both Royal Purple listings: fuel economy up by an average of 3.2 percent and horsepower up by an average of 2.6 percent, with hydrocarbon, NOx and CO emissions down by 12, 13 and 18 percent on average.
Do any of these additives state a warranty?
No. None of the four listings states a warranty term.
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