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The Best Fuel Additives for 4-Stroke Outboard

Written by Anthony Roberts / Fact checked by Jonathan Larson

To any boater who has had the privilege of enjoying the perfect motor and fuel additive pairing, having to do without the latter would almost always mean a less than optimal setup. It’s like spaghetti and meatballs or mac and cheese. Can we really blame them for the way ethanol and carbon from most fuel products wreak havoc on engines?

best fuel additive for 4 stroke outboard

This rings true even for those looking for something more specific, like the best fuel additive for 4-stroke outboard boat motors. With the right setup, you’ll be able to tell the vast difference it makes in the motor’s fuel efficiency, preventive maintenance, and overall performance.

In case you happen to be looking for the same combination that’s right on the money, reading my review of top-rated fuel additives may very well be all you need to do.

<strong>Top 1</strong>

Sea Foam SF-16

+ Easy to use
+ Takes care of rough idling
+ Improves overall engine performance

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<strong>Top 2</strong>

STA-BIL 360 22240

+ Slightly boosts fuel mileage
+ Aids in smooth engine performance
+ Consistent ethanol issues like corrosion

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<strong>Top 3</strong>

YAMAHA Fuel Additive

+ Great value for money
+ Well-recognized brand
+ Markedly improves performance

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Top 10 Fuel Additive for 4-Stroke Outboard Reviews

1. Sea Foam SF-16 Motor Treatment

A true classic, Sea Foam’s no-nonsense usage, performance, and guaranteed results make it one of the safest options for boaters.

This product served as my sweet introduction to the wonders of fuel additives. Back then, the brand’s claim that you only needed to add it to your gas or diesel fuel was what hooked me. It’s basically a pour-and-go setup.

It’s safe to say that I got more than what I bargained for. I saw the immense difference it made on my boat’s already fuel-efficient Yamaha outboard motor. This gas for 4-stroke outboard boosted my fishing boat’s MPG further, by as much as 3 miles, to be exact. As a regular fisher, this is always a welcome bonus for me. This oil treatment allows me to cover greater distances while bringing plenty of perks with me too.

I also noticed that it took care of the occasional rough idling I was getting before. I admit that it’s a fairly old motor, going for 4 years already. Even so, I’m betting it was more of a dirty fuel injector issue, and this product took care of it after the first tune-up and clean-up. I’ve made it a point to add it with every tankful refill I do for the performance boosts.

My only real gripe is the slightly pricey compared to other products. I can empty the entire 16 oz. in one go. Based on my boating habits, it can be quite the wallet-buster in the long run.
  • Easy to use
  • Consistently delivers results in fuel efficiency
  • Takes care of rough idling
  • Improves overall engine performance
  • Pricier than most
If you don’t want to go through all the trouble solving a 4-stroke engine problem, taking the ever-reliable Sea Foam marine pro additive is a guaranteed choice. It saves you time and from all the hassle of finding the correct solution.

2. STA-BIL 360 22240 Marine Fuel Stabilizer

The right fuel additives for outboard motors should be as easy to use as they are able to provide the full-blown benefits of fuel stabilizers. If I could name one good example of a product that deserves that label, STA-BIL 360 marine is often the first one that enters my mind.

I can’t dodge ethanol fuel products for my boat completely, with the sheer amount of these products in the market. What’s good is that there are ready workarounds for the said issue, and this fuel stabilizer basically addresses it head-on. For the amount of expensive damage that ethanol can deal on my vessel’s outboard engine, this is virtually the more economical, long-term route.

It also hits two birds with one stone since the local, extreme weather in the southeast USA where I live may contribute to the damage as well. I’ve been using the one-gallon variety of this product for a long time now, and I’m still not seeing any tell-tale signs of corrosion.

I may have already gotten used to it, but I can safely say that my charter boat’s 4-stroke engine runs cleanly and smoother when compared to other boats I’ve ridden. Besides the smoother performance, I also get more fuel mileage, though it’s only a subtle difference (around 2 more miles) based on a small test I did. Even so, this benefit is one of the main reasons why I can’t make do without great outboard fuel additives anymore.

My complaint about this additive, especially the one-gallon variant I frequently buy, is a very minor one. It doesn’t use the easier-to-pour squeeze container that the other selections have.
  • Great for boats with consistent ethanol issues like corrosion
  • Slightly boosts fuel mileage
  • Actively maintains fuel quality and boat engines
  • Aids in smooth engine performance
  • The one-gallon option doesn’t use a squeeze container
For a thorough ethanol treatment for boats and a remarkable boost in performance, you’d be hard-pressed to find a product that delivers as much quality and bonafide results as this one.

3. YAMAHA ACC-RNGFR-PL-12 Fuel Additive

This Yamaha concoction is a potent remedy for 4-stroke outboard motor ills and can perk it up like a potent caffeine energy boost in the morning — only, it lasts a good while.

I bought this fuel additive after my 9-year-old 30HP Yamaha outboard started showing signs of sputtering. It took almost three visits to my local repair shop before I figured out that I shouldn’t have been all too eager to listen to every piece of advice the mechanic made. I scoured the net for a few days after the issue remained unsolved, and long story short, that excursion led me to this product after a few recommendations.

The fact that it was made specifically for 4-stroke engines is what drew me. Ultimately, I’ll always give it credit for solving the idling issue my boat’s motor and I endured for almost a month. I’m more than willing to rain praises on products that take the time to provide more details about their capabilities and, more importantly, deliver what they promise. My boat’s engine has never sounded this smoother for a long time.

I also discerned a notable improvement in the speed of my vessel after the first few bottles. Unfortunately, I can’t say much about the alleged protective capabilities it has since I’ve only used it for 3 months. However, since we’re talking about a brand as established as Yamaha here, I’m confident that it does a fine job in that regard, too.

It’s downright expensive for that reason, which I definitely hate. But for what I got, I can say that it delivers great value for money. Besides, I paid way more for those consecutive trips to the mechanic, even though I ended up getting nothing from it!
  • Specially formulated for 4-stroke engines
  • Solves a common outboard motor issue
  • Markedly improves performance
  • Well-recognized brand
  • Great value for money
  • Expensive
Like a potent elixir, I know that I can always rely on this fuel additive when my boat engine starts coughing and showing other tell-tale signs.

4. Star Brite 14308 Star Tron Enzyme Fuel Treatment

Cost-efficient and more affordable, Star Tron’s additive is a must for anyone who wants to make the most out of their fuel and hard-earned bucks.

This basically eats up the ethanol that may be present in the gas you’re using. Of course, that’s a good thing because I’ve had boat fuel go to waste after as little as two weeks so that it won’t damage the motor. You can only imagine the money I save from relying on this neat fuel treatment, which extends my fuel’s life for up to 2 years.

I discovered that it works well with Sea Foam, particularly when keeping the quality of my boat’s gasoline. Even when I leave my vessel idle for a couple of months, it fires right up in the first crank as if I only used it yesterday. I attribute the longer fuel life mostly to my decision to combine it with Sea Foam since I don’t get the same longevity when I use either one on their own.

I also use this to restore the old, extra fuel that I tend to store when I don’t have as much time fishing and boating. I even found it ideal for my lawnmower and chainsaw. More importantly, I can confirm that it works best for my boat’s small 4-stroke engine, as evidenced by the stable performance I get every time.

I hope the brand would consider including a way to measure how much I’m pouring as I tend to be meticulous with my mixtures.
  • Efficiently takes care of ethanol problems
  • Works well with Sea Foam
  • Affordable and allows you to save more on fuel in the long run
  • Optimal engine protection
  • Versatile usage
  • Could use a measurer
Though I won’t name them directly, I feel that this product is a far superior option than a few of the additives listed here, especially if I crunch the numbers.

5. Yamaha ACC-RNGFR-PL-32 Outboard Fuel Additive

For anyone with 2-stroke or 4-stroke outboard engines made by this brand, you don’t have to look further than Ring Free. It’s their power juice.

I thought it’s only logical to buy this for my 5-year-old Yamaha outboard when it started showing signs of hesitation problems. Admittedly, I wasn’t a fan of the price tag, and this is coming from someone who usually exceeds 70 hours of active boating time every season. Still, it’s a once or twice per summer purchase, so it’s not really a big thing.

Going back to what problems it solved, it pretty much took care of any ethanol problem I suddenly encountered when the usual signs showed up. I usually go the shock treatment route and pair it with Sea Foam when using this mix, and it’s always brought about solid results. The engine began running whisper-quiet and the air screens and filters were kept clean and working right as rain.

Low-speed idling became smoother. I also found that I don’t need to replace the spark plugs anymore, even if I subject the engine to shock treatment as long as I use this additive with Sea Foam. Incidentally, I also recommended this additive to a fishing buddy of mine who happens to have a 15-year-old engine, and he pretty much got the same results.

I wouldn’t mind the price if I don’t fish or boat as frequently as any casual boater out there. Even so, I can safely say that I get my money’s worth with every purchase.
  • Specifically created for outboard engines
  • Keeps filters and air screen clean and in top shape
  • Can be used to restore the performance of old Yamaha engines
  • Pairs well with Sea Foam to keep spark plugs clean
  • Great value for money
  • Costly for frequent boaters
This fuel additive for Yamaha outboard engines is special in more ways than one, proven by its perks. Once you give it a try, you’ll see the wonders it brings to that type of engine with that brand’s label.

6. Mercury 8M0047920 Quickare Fuel Treatment Additive

Anyone with a Mercury outboard engine should listen to dealers’ recommendations and opt for Quickare’s timely solutions to most ethanol-induced outboard issues.

This fuel additive’s primary strength lies in its specialty in its brand. It may not be as versatile as other options like Sea Foam, but I wouldn’t trade this for any other treatment if I have an outboard made by this brand. Almost any applicable boat that I used this on, whether mine or owned by someone I know, takes care of all the common ethanol and deposit issues.

I always appreciate having a safer option that meets manufacturers’ recommendations for the additives I use for 4-stroke outboards. I’m glad I won’t have to have that dilemma when I need one for anything made by this brand. I get smooth-as-butter performance from my outboard and sound that’s just music to any consummate boater’s ears.

I haven’t tried it on outboards made by other brands but I have a friend who can attest that it works better than STA-BIL. Some of the feedback on Amazon proves this as well.

I do have to critique the relatively shorter duration of its ability to keep fuel fresh. I like that the brand is transparent about it when they state that it maintains the fuel for up to 3 months. Nonetheless, that’s rather too short a time compared to other additives I’ve used.
  • Great in tackling ethanol and deposit issues in Mercury outboards
  • Satisfies manufacturer’s recommendations
  • Assures smoother and better-sounding motor performance
  • Works better than STA-BIL according to a few users’ feedback
  • Stabilizing effect not as long as other fuel additives
This brand-centric additive is as solid as most of the excellent products on this list come when delivering their coveted effects.

7. Star Brite Star Tron Enzyme Fuel Treatment Concentrate

Any boater having perennial problems with ethanol gasoline, not least of which are costly engine repairs and low fuel storage life, should know that a trusty partner can be found with this additive. It delivers a plethora of advantages seldom enjoyed by boaters who rely on fuel additives.

For one, I rarely get no less than two to three years of extended ethanol-gasoline life every time I pour this in my fishing boat’s 4-stroke outboard engine. I even use it for any other vehicle with small engines, especially if I have no other choice but to use ethanol fuel. I’ve been using it for close to three years on my boat, and I haven’t noticed any damage to the whole fuel system yet.

I like that it saves me from the hassle of cleaning my carburetors regularly. Any time saved as a direct result of a product’s effects is gold for me. Moreover, I barely have to pull more than once to get the engine running like it’s as good as new as long as I’m using this additive.

I think it’s important for the brand to start paying attention to the bottle design. I totally agree with other users who complain about the amount of spillage I get almost every time I try to pour this product from its one-gallon container.

That is a big no-no, considering the fact that I tend to pay the higher cost than more well-recognized brands out there. The bottle issue is unfortunate because I regard this product as a solid alternative to them. I just console myself that I can always rely on a syringe to get more accurate measurements.
  • Proven to keep ethanol gasoline for up to 2 to 3 years
  • Cost-efficient and effort-saving in the long run
  • Helps the engine to start up quickly
  • Works with most small engines
  • Hard to pour without spilling
  • Slightly more expensive
Despite its flaws, I won’t be willing to trade this gas additive for outboard motors for anything that can’t surpass its perks.

8. Mercury 8M0047931 Marine Quickleen

Quickleen by Mercury proves the point that it’s infinitely better and safer to opt for specialized formulations made for boat engines in most cases.

I have used numerous fuel additives and stabilizers for my 4-stroke outboards before. However, only a few products are as reliable and as adaptable in the specific boat problems it can address as this formulation. I continue to use this for most of my outboards, 2-stroke and 4-stroke of varying horsepower, and let’s just say it has spared me from numerous trips to the mechanic.

I’ve used this to take care of hesitation and misfire problems. Even back when I wasn’t too knowledgeable on how to clean injectors yet, I remember simply pouring this in one 100HP 4-stroke outboard of my powerboat fixed the problem in no time. I’d definitely use this first before deciding to make any permanent changes like plug and coil replacements to spare me from any unneeded expense.

In most cases, I found that you only need to be patient to see the results, especially if you want a spick-and-span fuel system. I’ve tried it out on Yamaha and Mercury outboards and get the same benefits as any other fuel stabilizer, if not more considering the money-saving advantages.

I can’t say much about the brand’s claim that it extends the spark plug’s life. I can attest, though, that I rarely find the need to replace it unless I subject the motors to shock treatment, which isn’t exactly a regular thing.

While it’s affordable compared to other products, I feel it pales in comparison to other brands when other brands. This is because I almost always have to leave as little fuel as possible in the tank to make the most of its fuel-keeping benefits.
  • Works well for Yamaha and Mercury outboards
  • Addresses numerous outboard-related problems
  • Helps you save more money from repairs and replacements
  • More budget-friendly
  • Doesn’t keep the fuel as well as other brands
If your primary concern is to get an additive that will fix an issue related to a 4-stroke engine or if you’re going for specificity, then I highly recommend this product.

9. Quicksilver 858080Q03 Power Tune

This neat spray could magically whisk away any carbon-related malady your outboard might be encountering. A good dose is often enough to make my engines be in tip-top condition again.

This product spares me from relying on usual shock treatments to remove any excess carbon buildup in the carburetor of my Evinrude outboard. I love that I basically only need to spray it on the carburetor to get the job done. Of course, I still need to burn out all the old fuel, but almost always, it makes a vast difference in the engine startup and operation afterward.

This has since become my favorite carburetor cleaner for my 4-stroke outboards. Where others have failed in removing all that stale, old gas, this one proved to be an exception. The moment I sprayed it the first time and those trademark foams pop up, I know I had a wise choice. Almost any part of your fuel system with any carbon buildup will benefit from this potent spray.

The opposite only means costly teardowns, which I’m glad I get to delay or avoid with the help of this product. It not only saves me money but plenty of time and effort, too. Sometimes, I even only do an overnight soak of one of my engine’s carburetors with this solution and get the same results.

It’s decently priced as well. I haven’t got major criticisms about it other than it could be packed better. After all, a past order of mine arrived with a broken nozzle.
  • Specially formulated for 4-stroke gasoline engines
  • Easy to use thanks to spray design
  • Excellent carburetor cleaner and decarbonizer overall
  • Saves time and effort and costlier expenses down the road
  • Packed poorly sometimes
I wasn’t kidding when I said that this product almost works like magic when functioning as a cleaner for outboard engines. Choose this if you need a quick carburetor cleanup.

10. LUCAS LUC10013 Fuel Treatment

I use this product as a go-to fuel treatment when I want to save money for improving my outboard engine’s performance and making the most out of my fuel. It’s got cost-efficiency written all over it.

Considering the prices of one-gallon fuel additives in the market today, this LUCAS fuel treatment is a godsend. It’s virtually a guaranteed performance boost and long-term fuel savings for less money. I travel 50 to 70 miles when cruising, and based on my tests, I get a slight but no less remarkable boost of at most 2 MPG with my boat.

It doesn’t hurt that I can use it for my trailers as well. I no longer go without this product for the way it makes my outboard engine run smoother and quieter. I can always hear the difference when I use this and when I don’t, and I can say as much for my trailers.

I even remember one time when I was riding in one of my friends’ boats and the engine started sputtering. Good thing we brought my trailer where I keep my stock of this nifty additive. Long story short, we added this stabilizer to the outboard before filling it up with fresh gas, and after around two miles of the motor coughing, the problem subsided altogether.

Through these benefits alone, I can confidently state that I already get my money’s worth every time I buy another gallon of this product. I wish it’s easier to know how much cleaner is going into the tank, though, and they could have easily added the measuring tools to the large bottle. Moreover, the bottle design makes it hard to pour directly.
  • Cheaper than others
  • Proven to increase gas mileage by a bit
  • Versatile, can support numerous types of vehicles
  • Quickly solves sputtering engine problems
  • Excellent value for money
  • Needs an accurate measurer
  • Bottle design makes it hard to pour
Many drivers and boaters find it hard to ditch this product for the cost-savings and engine-boosting advantages it imparts. I’m proud to say that I’m one of them.

Buyer’s Guide


Your purpose for using an additive on your boat’s 4-stroke outboard should be one of the main considerations when deciding the best type of product to go for. Do you wish to take care of problems usually associated with ethanol in fuel? Or do you simply want your gas to last longer and boost engine performance? Perhaps you want to decarbonize your boat?

As my review of the fuel treatment, cleaners and additives can prove, these products don’t share the same benefits, at least in certain cases.

Some choose to specialize in boat engines, while others are more versatile and can cater to numerous vehicle types and motor sizes.

It’s safe to say that you should be mindful of these exact advantages and know whether they apply to your exact situation or cater to your specific needs. Besides this essential factor, it won’t hurt to look at these areas as well:

Fuel and Engine Compatibility

Double-check whether the additive works for the brand of your 4-stroke outboard (e.g. Yamaha fuel additives outboards) as well as the type of fuel you use with it. Each product should tell you which types it optimally works with. If this information isn’t readily available, be sure to ask the manufacturer about it.

Ease of Use

Convenience shouldn’t be overlooked. Does the product require you to take extra, complicated steps just to deliver its benefits? How is the bottle designed? Does it help you make exact measurements so you can pour the precise measurement in no time with every gallon of fuel?

Duration of Stabilization

If you want your fuel to remain viable for as long as you want it to, you need to know the products that can fulfill that. Of course, you should also take into consideration any change in season that might impact that. Winter might render certain stabilizers less effective, at least, compared to their winter-formulated counterparts.

What is the Fuel Additive for 4-Stroke Outboard


Sea Foam is the most popular, safest, and what I would recommend for anyone who’s still trying out fuel additives for this type of engine. More or less, it delivers every major benefit your 4-stroke outboard can gain from a fuel additive.

However, I can say the same for a handful of other products listed here. Each one has its own strength, especially in the amount of money I save with their help and the engines they work best with. For this reason, I recommend them all.

Is Sea Foam Safe for 4-Stroke Outboard

It’s not only very safe but easy to use and recommended for most 4-stroke outboard engines. The brand itself has confirmed this on its main website. You can always pour directly into the tank without any issues. Most boaters use it to give their vessel’s motors a quick fix when they’re having carbon buildup issues. Usually, this is achieved through proper shock treatment.

Which is Better Sea Foam or STA-BIL

If I’m going to consider adaptability in numerous situations 4-stroke engines are placed in, I’d say Sea Foam is the winner. The rule of thumb is that Sea Foam tends to work better with smaller engines that might be more likely to be exposed to moisture, while STA-BIL is the exact opposite.

However, both are household names for a reason. I’ve found that STA-BIL is ideal if you’re planning to keep your boat idle and maintain its fuel for a long time, considering the way it works like antifreeze when stabilizing its fuel.


I hope that with the information I provided above, you now have a good inkling about what fuel to use in 4-stroke outboard engines and their ideal additives. To me, the best fuel additive for 4-stroke outboard is ultimately the one that consistently delivers everything you need from them while helping you save money, time, and effort when boating.

5/5 - (2 votes)