Ethanol Fuel & Florida Outboards: What Actually Goes Wrong
Most 'mystery' no-start and rough-idle calls Fox Marine takes in the spring come back to one thing: bad fuel. Florida heat + ethanol + boats that sit = problems. Here's what's actually happening in the tank and how to stop it.
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What ethanol does in a marine tank
E10 absorbs water out of the air through every vent. Once it absorbs enough, the ethanol/water mix separates from the gasoline and sinks to the bottom of the tank — exactly where the pickup tube sits. That layer is corrosive, it doesn't burn well, and it eats fuel-system rubber that's older than about 2005.
Symptoms we see
- Hard starting after the boat has sat 3+ weeks
- Hesitation or stumble above 3,500 RPM
- Visible water or brown gunk in the water-separator filter
- Cracked primer bulb or fuel hose weeping at fittings
- Check-engine codes for lean condition on one bank
Fox Marine's prevention checklist
- Buy ethanol-free 90 octane when you can (most Vero/Sebastian marinas carry it)
- Treat every tank with a marine stabilizer (Yamaha Ring Free + Sta-Bil 360 Marine)
- Keep the tank above ½ full when storing — less air = less moisture
- Change the 10-micron water-separating filter every 100 hours OR after any suspect fill
- If the boat will sit > 60 days, fog the cylinders and add stabilizer at the recommended storage dose
FAQs
Is non-ethanol gas worth the extra cost?
For boats that sit between trips — yes, every time. For a boat that burns through a tank weekly in season, regular E10 with stabilizer is fine.
How long does gas last in a boat tank?
Treated and sealed, 6 months is realistic. Untreated E10 in a vented marine tank in Florida heat starts degrading at about 30 days.
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