A service colleague has examined fuel additives several times in recent years. He tested their ability to prevent the potentially harmful precipitation or separation of water in long-stored E-10 fuels (gasoline containing 10% ethanol). A year later, he again analyzed diesel fuels without additives and gasoline additives, focusing on corrosion prevention that can damage metal parts and cause solid deposits in the fuel system.
In diesel engines, deposits appear in the fuel tank over time due to oxidation, dirty fuel, and bacterial growth. Multi-stage filtration is usually sufficient to collect solid materials in diesel engines. However, in gasoline engines, solids often appear spontaneously in the carburetor, regardless of how many filters are used.
For this test, the colleague analyzed samples from several engines — none of which had used aftermarket additives: two 2001 Yamaha 9.9 HP four-stroke, a 2006 Mercury 6 HP four-stroke, and a 2002 Mercury 3.5 HP two-stroke. The following contaminants were found, expressed as a percentage of total mass: aluminum (21%), zinc (8%), calcium (10%), iron (5%), and copper (<100 ppm).
The presence of metallic elements in solids does not necessarily prove they originated from corrosion. Such solids can enter the fuel tank during refining or filtration and are unlikely to be removed by evaporation or condensation. There are also polymer additives that can dry out and form gels — mechanics may encounter this during carburetor cleaning. Some studies also found sodium salts present in the fuel.
The presence of aluminum requires special attention. Both fuel tanks and carburetors often contain aluminum, and ethanol-blended gasoline is associated with aluminum corrosion. Ethanol acts as a weak acid, attacking the oxide layer that usually protects aluminum from corrosion. This creates a reactive surface where dissolved oxygen in water can rapidly oxidize. In the absence of oxygen, ethanol itself can act as an oxidizing agent, though the process is slower.
If the conditions are right, this two-step chemical process can lead to pitting and structural damage, eventually creating holes in the fuel tank. Corrosion byproducts can block the fuel flow. Corrosion inhibitors added during refining slow this process — but the question remains whether aftermarket additives provide additional protection.
Galvanic corrosion must also be considered. All tested carburetors contained some brass components (the Yamaha engines had brass drain plugs). The potential difference between aluminum and brass on the galvanic scale is 0.45–0.5 volts, depending on the alloy. In “dry” fuel, there is no conductivity and thus no corrosion. However, E-10 fuel can dissolve moisture and saltwater, providing the key element for corrosion: water.
Laboratory corrosion testing is a highly developed science. The ASTM (American Society for Testing and Materials) and NACE (National Association of Corrosion Engineers) define standard testing methods. However, laboratory methods often focus on product development and quality control, and don’t always replicate the slow chemical processes that occur over time.
(For example, in 1995, General Motors introduced a new coolant called Dexcool. Despite extensive testing, it was never tested with certain sealants or other coolants. The result: seal failures and system damage in many vehicles — leading to later reformulation.)
The goal was long-term testing of fuel additives. Instead of adding heat, oxygen, or chemicals, we simulated time itself. Using a controlled laboratory setup, we incorporated methods used to test engine coolants and fuel additives.
To accelerate the test, we added a small amount of seawater (0.03%) to 100 liters of E-10. This helped simulate real-world marine exposure.
Saltwater intrusion is clearly dangerous — even short exposure can cause damage. Ensure the fuel cap is tight, and avoid using incompatible additives that may worsen corrosion.
Ethanol-based fuels are less lubricating and degrade faster than traditional fuels, reducing valve lubrication and octane rating. This can cause valve seat recession, engine knocking, and accelerated rubber component wear.
They are also hygroscopic and corrosive to certain metals, rubbers, and plastics.
Proper fuel treatment is essential for classic cars, motorcycles, and marine engines, ensuring:
For all gasoline engines not compatible with E5/E10 biofuels or those originally designed for leaded fuel but now running on unleaded fuel.
Consult your service provider, ask for advice, and maintain your engine regularly.
We hope this helps.
(Source: Practical Sailor)
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