Managing Fuel System Rubber Components & Seals with Ethanol Exposure

The primary culprit behind NBR (nitrile) rubber swelling or cracking isn't just the fuel, it’s the chemistry of storage.

The Cause: Ethanol and Water

• The Ethanol Factor: Modern fuels blended with ethanol naturally affect rubber products. However, US ethanol levels are generally consistent and well-monitored.
• The Water Catalyst: The real issue arises when water enters the fuel system. Water can bond with ethanol to create a mixture that significantly accelerates the absorption rate in NBR seals.
• The Result: Amplifies several effects on NBR rubber. This leads to:
  • Increase swelling (dimensional changes).
  • Plasticizer Extraction (Rubber may first soften which can cause sticking to components and functional problems. Then the rubber can become brittle over time, which leads to cracking and leaking).
  • Accelerated Degradation (Reduced product lifespan).
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Best Practices for Maintenance

To ensure the longevity of the rubber components that are exposed to fuel, especially in vehicles that sit for extended periods, follow these steps:

• Monitor Fuel Quality: Be mindful of the ethanol content in your local fuel.
• Prevent Phase Separation: Keep fuel tanks full to minimize condensation (water buildup) during storage.
• Fresh Fuel is Best: Avoid using old or "stale" fuel, as the chemical composition shifts over time, increasing the risk to rubber components.
• Use Fuel Stabilizer: When your vehicle is stored (not operated) within a period of three months. 
• (Store-N-Start 220-375)