Seafoam vs Stabil: Which Fuel Stabilizer is Better?

Fuel stabilizers are organic compounds that are added to gasoline during the refining process. Stabilizers keep the gasoline stable and prevent it from separating. The need for a fuel stabilizer arises when fuel has to be stored for a long time. Lawnmowers, motorcycles, snowblowers, RVs and classic cars often store gasoline for a longer time and need additional fuel stabilizers as additives to avoid damage. The best fuel stabilizers work in ways that your engine would never imagine, helping you make your car run smoother, longer, and with less maintenance. When it comes to battling the EOT (end of travel) fuel issues in today’s trucking industry, there are two fuel stabilizer products that come to mind – Seafoam vs Stabil. Which one is better? Well, let us take a look at both of these products and understand how they differ in terms of science, application, and cost. This way you can make your own decision as to which fuel stabilizer is right for you.

The main difference between stabil and seafoam fuel stabilizers is that seafoam acts as both fuel stabilizer and fuel-system detergent. Seafoam is all alcohol (isopropyl alcohol) that is used as a solvent and a couple of drops of light 10-weight oil in it is added as a very light lubricant while Stabil has no ethanol. Stabil only acts as a fuel stabilizer. Seafoam acts as an oxygenator to help burn off and dissolve combustion chamber deposits like carbon bits and sludge while Stabil keeps the fuel fresh by extending the storage life of gasoline and helps prevent some kinds of ethanol-related fuel issues. 

Want to know which oil is better for your engine? Check my guide on 5w20 vs 5w30

Sta-bil 360
Sta-bil 360
Sta-bil Regular
Sta-bil Regular

Why Do We Need Fuel Stabilizer?

The main problem with gasoline is that it’s unstable and prone to oxidation. As a result, it may become rancid, lose its flavor, turn brown, smell bad, and become contaminated with water and dirt. 

A solution for storing gasoline for a long time is to use a gasoline stabilizer. Stabilizers prevent oxidation by absorbing oxygen, neutralizing acids, and reducing volatility. They also prevent the formation of sediment and dirt and reduce the chances of fire. They may be added to gasoline at the filling station or you can buy them at any local store.

Sta-bil vs Seafoam Comparison 

The most important thing to consider when choosing between Sta-bil and Seafoam is their application, their effectiveness, and their cost. Seafoam and Sta-bil are both designed to protect your engine, but they work differently.

Below, I have made a detailed comparison between Stabil and Seafoam fuel additives so that you can decide which one works better for your engine.


Seafoam is better known for cleaning the engine as it mainly targets carbon deposits in the engine’s fuel system, such as the carburetor jets, fuel injectors and passages. Seafoam is amazingly good at cleaning sludge out of a motor and gummy resins as you can also add it to the crankcase where motor oil is present. 

Here is what a user says about Seafoam:

“I put 1/3 in my oil and 2/3 in my gas on a ’93 geo prizm(120,000m). I ran it for 1000 miles or so… had oil changed. It cleaned up so much gunk I swear my mileage went up 3 or 4 miles a gallon.”

Moreover, people claim that seafoam is good for higher-mileage vehicles and is no better than a placebo for vehicles that are lower-mileage and thus don’t yet have carbon buildups. Apart from dissolving the deposits in the engine, Seafoam is supposed to produce a lot of smoke from the engine as it contains 40-60% of heavy pale oil that is going to smoke no matter what. 

On the other hand, people like to use Sta-bil as a fuel stabilizer to prevent fuel separation when they let their engines sit for months. Here is what a user says about his use of Sta-bil:

“I use Sta-bil Marine, and Techron. I pulled apart a boat motor carburetor last fall, in a boat that sat in my backyard for a decade. I had used this combo while running the boat in prior years. The carb looked brand new. No tarnish, no deposits, perfectly clean.”

Unlike Seafoam, Sta-bil doesn’t contain alcohol. The company has not shared the exact ingredients they have used for the formulation of Sta-bil as these are the brand’s proprietary materials. According to the experiments done by the people, Sta-bil is a hydrotreated isoparaffinic solvent heavy naphtha, petroleum distillates, mineral oil, and low odour cleaning solvent. The exact proportion of chemicals in Sta-bil is still not known. Once Sta-bil is added to your fuel it separates and creates a thin film on top of the fuel which keeps out the air and more importantly keeps out moisture.


If you’re using ethanol-free gasoline, it is safe to use Seafoam in the gas tank. 1oz of seafoam in one gallon of gasoline is fine for small engines. You can do 1/3 through the throttle and 2/3 in the tank for better performance. Seafoam also has some octane booster and fuel stabilizer (Naphtha) in it as well to make sure it is safe to pour into the gas tank. If you can also use seafoam in oil, use it an hour or so before an oil change. Let the engine run and circulate the Sea Foam to clean gunk, etc from your system. Make sure to change your oil down the road. Changing of oil is recommended after using Seafoam in crankcase because a large amount of built-up junk cleaned by the Seafoam can clog up your oil flow.

The myth about Seafoam is that it helps remove water from the fuel. This is not correct. Alcohol is actually hydrophilic, which means it attracts the water. When you add seafoam, which contains 10-20% of isopropyl alcohol, to fuel that has become contaminated with water, the water gets attracted to the alcohol. Since the water is bonded with the alcohol, water is then dragged along into the combustion process by the alcohol and is flashed off as steam. 

There are two types of Sta-bil stabilizers. One is Sta-bil 360 (marine) and regular Sta-bil. You should use 1 ounce of Sta-bil 360 per 10 gallons of fuel and 1 ounce of a regular Sta-bil per 2.5 gallons of fuel. Unlike Seafoam, you shouldn’t add Sta-bil through air throttle passage, vacuum lines, and crankcase. You should only pour Sta-bil into the gas tank. Beware, when adding SeaFoam to the air intake, harmless plumes of white smoke will come out of the exhaust.

If you have gasoline in your tank that has ethanol i.e. E10, you can use Sta-bil, but only in the recommended amount. Adding more, again, can cause problems. If you use Seafoam with E10 gasoline, it can harm rubber and plastic parts in the carburetor. 

Effective Duration to Stabilize Fuel

Regular gasoline has a shelf life of 3 to 6 months. So, it matters a lot to determine which one between Sta-bil and Seam will keep the fuel fresh for a longer time. Sta-bil regular claims to stabilize the fuel for up to 2 years and Sta-bil Marine claims to stabilize the fuel for up to 12 months. According to the Seaforam’s site, Sea Foam will clean carburetors, and fuel injectors, clean carbon, gum, and varnish deposits, add lubricity to fuel, and stabilize fuel for up to 2 years.

Comparison Table of Seafoam vs Sta-bil

Used as a fuel stabilizerActs as a fuel detergent and fuel stabilizer. But, majorly used as a fuel detergent
Can be used poured only into the gas tankCan be poured into the oil, gas tank and throttle body
Contains proprietary chemicals formulated from naphtha, mineral oil, paraffin etc.Contains:
40-60% Pale oil – Thin oil that’s why it smokes
25-35% Napata – A basic solvent Can find in some carb cleaners
10-20% IPA (Isopropyl alcohol) – Same active ingredient in rubbing alcohol.  
Keeps the fuel fresh and prevents it from separationBurns off the carbon deposits and liquifies the sludge
Can be used with the E10 fuelShould be used with ethanol-free fuel. However, if you insert Seafoam into oil, it’s fine to use
Sta-bil should be used 1oz per 10 gal of fuel      Sta-bil 360 should be used 1oz per 2.5 gallon of fuelSeaFoam should be used 1-2 ounces per 1 gallon of fuel
Perfect for off-season storage of fuelCan be used every couple of months to clean the engine

Final Thoughts About Seafoam vs Sta-bil

So, there is a strong competition between Seafoam and Sta-bi which has made it difficult for me to decide which one of these is better for your engine. I would like to say that Sta-bil is the perfect fuel for engines which sit for a long time i.e. for off-season storage On the other hand, Seafoam is more likely used for running and cleaning out stuff like carbon deposits and engine sludge. You can also use SeaFoam as a fuel stabilizer for storing the fuel. But you should ensure that the fuel is ethanol-free.

I would recommend using Sta-bil Marine as it performs better for water moisture, and is more suitable for harsh and humid environments.

Here is what a user says when he used Sta-bil to store the fuel for a long time.

“I’ve had 40 gallons of regular gas stabilized using Stabil for over 12 months. I did run 3 different vehicles with it and had no issues.”

Stabilizing fuel means helping fuel resist the oxidation and evaporation of petroleum hydrocarbons. Oxidized fuel, known as gum and varnish, is the most common cause of poor engine function. Unlike most other gas and diesel fuel stabilizer products, Sea Foam Motor Treatment is also a high-temp cleaner and upper cylinder lubricant. SeaFoam dissolves gum and varnish that has already formed in the engine, overcoming lost engine power and function. More, Sea Foam resists fuel evaporation and adds petroleum lubricity and corrosion protection to engine parts. Seafoam only contains highly-refined petroleum ingredients. It does not have harsh detergents or abrasive chemicals that can harm your engine.


Can You Mix Stabil and Seafoam Together?

Some people mix Seafoam and Sta-bil when they have to clean the sludge and carbon deposits in the engine. It is fine to run Seafoam through the engine to clean carbon deposits if your fuel has been treated with Sta-bil.

Will Sea Foam Harm O2 Sensors?

If Seafoam is used in adequate amounts, it cannot harm the oxygen sensor.  Seafoam is basically naphtha and sweet oil which aren’t going to do as much damage to the O2 sensor. However, the O2 sensor is damaged while using Seafoam if there are too much problems in the engine. Also, keep in mind that using carb cleaner i.e. Seafoam you can clean the carbon build-up from the O2 sensor’s louvered cover, but you don’t actually clean the sensor, itself. Moreover, even if you could clean the sensor, itself, there’s no guarantee that doing so would restore the sensor to its like-new condition and, therefore, readings.

Will Sea Foam Damage Seals?

Seafoam does not damage seals. In fact, in high mileage or old engines, there are too much carbon deposits that they act as a seal to prevent leakage. Older engines make a better seal in the bore with a little carbon in there. Using Seafoam will just clear away elements that might be hiding evidence of the failure of those parts.

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