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Ethanol Defense & Storage Guide

Ethanol attracts water. Water kills engines. Here is how to protect your classics, boats, and small engines in .

The Problem: Most pump gas is E10 (10% Ethanol). Ethanol is hygroscopic, meaning it pulls moisture directly from the air. If your car/boat sits for more than 30 days, that moisture can separate and corrode your fuel system from the inside out.

Quick Picks: Best Stabilizers

Product Best Use Case Why We Picked It
STA-BIL 360 Protection Classic Cars Releases a vapor to coat the tank above the fuel line (prevents rust).
Star Tron Enzyme Fuel Treatment Marine / Boats Uses enzymes to break down water clusters. Essential for humid environments.
K100 Fuel Treatment Small Engines Heavy-duty formula that can actually reverse minor phase separation.

The Science: What is Phase Separation?

Think of a salad dressing separating into oil and vinegar. That is exactly what happens to E10 gas.

  1. Absorption: The ethanol in your gas tank absorbs humidity from the air vent.
  2. Saturation: Once the water content exceeds roughly 0.5%, the ethanol can no longer hold it in suspension.
  3. Separation: The water and ethanol bond together and drop to the bottom of the tank (because they are heavier than gas).

The Damage: Your fuel pump sits at the bottom. When you try to start the engine, it sucks up a concentrated cocktail of water and alcohol. This causes instant corrosion, lean conditions, and can hydrolock injectors.

Storage Strategy: Wet vs. Dry?

The most common question we get: "Should I store my car with a full tank or an empty one?"

Strategy A: The Full Tank (Recommended)

Method: Fill the tank to 95%+, add a stabilizer, and run the engine for 10 minutes to circulate it.

Pros

  • Minimizes "headspace" (air) in the tank, limiting moisture absorption.
  • Prevents tank walls from flash-rusting (if metal).

Cons

  • If stored for >12 months, the fuel will eventually go "stale" anyway.

Strategy B: The Empty Tank

Method: Drain the tank and run the engine until it dies.

Verdict: Only do this for small engines (chainsaws, mowers) with plastic tanks. For cars, leaving a steel tank empty exposes the metal to air, inviting massive rust issues.

Marine vs. Automotive Stabilizers

Boats live in the worst possible environment: high humidity and vented fuel tanks.

  • Marine Stabilizers (like Star Tron): Focus on emulsification or enzyme breakdown. They try to disperse tiny water droplets so they can pass through the engine harmlessly.
  • Auto Stabilizers (like STA-BIL): Focus on oxidation prevention (keeping the gas fresh) and corrosion inhibition (stopping rust).
Tip: You can use Marine stabilizer in a car, but it's often overkill (and more expensive). Stick to the right tool for the job.