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Maintenance 10 min readJune 3, 2025

The Complete Inboard Engine Winterizing Checklist

A step-by-step guide from our verified marine mechanics. Save hundreds next spring by doing it right this fall.

T
Tony Greco
Certified Marine Mechanic
πŸ”§

Why Winterizing Matters

Improper winterization is the single most expensive mistake a boat owner makes. Cracked engine blocks, corroded fuel systems, and seized through-hulls can turn a routine winter into a $5,000–$15,000 repair bill in the spring.

The good news: done correctly, winterization is straightforward.

The Checklist

Engine

  • Change engine oil and filter while warm
  • Flush raw water cooling system with fresh water
  • Run antifreeze through raw water circuit until pink at exhaust
  • Fog all cylinders and carburetor with fogging oil
  • Remove spark plugs, spray fogging oil, reinstall
  • Disconnect battery or connect to trickle charger
  • Fuel System

  • Fill tank to 95% capacity (prevents condensation)
  • Add fuel stabilizer β€” run engine 10 minutes to distribute
  • Inspect fuel lines for cracks or softness
  • Close fuel shut-off valve
  • Cooling System

  • Drain freshwater cooling system if equipped
  • Check hoses and clamps for wear
  • Inspect heat exchanger zincs
  • Hull and Drive

  • Inspect anodes (zincs) β€” replace if less than 50% remaining
  • Lubricate steering cable and helm
  • Grease propeller shaft
  • If trailered, chock the trailer and store propeller
  • Interior

  • Remove all food, cushions, and electronics
  • Leave cabin hatches cracked for ventilation
  • Cover bilge with bilge antifreeze
  • When to Call a Pro

    If your engine is exhibiting unusual smoke, the impeller hasn't been changed since 2 seasons ago, or you've had overheating issues during the season, winterization is an excellent time to have a professional assessment.

    Check Boatee for rated marine mechanics in your area with community pricing β€” before you call.

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