Ethanol is hydroscopic — it likes to absorb water. If water does get in, the ethanol in the gasoline will absorb it. That's acceptable with small amounts of water because it will simply be burned in the combustion cycle. But ethanol can only absorb so much water. When it becomes completely saturated, phase separation occurs, and the corrosive ethanol-water mixture sinks to the bottom of the tank. If the engine is run, this mixture can damage seals, O-rings, injectors, and other delicate engine parts. The upper "gasoline" layer will be depleted of ethanol and have a reduced octane level, which can also cause engine problems.
If you can't empty the tank completely, then top it off and add a good fuel stabilizer. Run the engine for 10 minutes to distribute the stabilized fuel through the engine and fuel lines. Make sure the seals in the filler cap are still intact, the cap is closed tightly, and the vent for the tank is not blocked.
Once phase separation occurs, there is no way to reverse it. No additive can rejuvenate bad gasoline. Bad fuel is bad fuel, and the only option is to dispose of it.
"Regular service to your boat is cheaper than waiting."
"The best time to service your boat is at the end of the boating season; prior to storage."
"The purpose of winterization is not just freeze protection, it is also storage damage prevention."
"Schedule with us in advance to reserve your preferred time for service."
Many boats are damaged or even destroyed every year because the systems aren't given the attention they deserve. While everybody knows that the engine and freshwater system must be winterized, there are many small but critical jobs that should be done. Some various winterizing chores that are most likely to be overlooked are not only freeze protection, but storage damage prevention. Are the engine fluids contaminated with water or acidic from use? Is your battery low on charge or connections corroded? Have you checked to see if your spark plugs show any signs of water? Letting an engine sit during the off season without taking some time to prepare it can be disastrous.
Everyone knows the term winterize, but how familiar are you with all that it entails? Did you drain the sea water housing, block, manifolds, oil cooler, live well, water system, shower and make sure there is no residual water in your stern drive? Is your bilge holding water creating condensation to rust your engine parts.
Refer to your owners manual for specific draining requirements for your engine & drive package. It will also show you where the drains are located to make sure you have drained the unit completely. Always make sure water is draining when removing drain plugs. No engine is self draining. If no water is draining there may be debris or silt plugging the drain hole.
Is the boat covered properly? A winter cover is terrific protection if it's adequately ventilated. With most boats, lack of ventilation beneath the cover causes mildew or even rot problems below. The problem occurs most often when shrink wrap covers aren't ventilated. Any cover that isn't well-supported will accumulate snow and water, which adds considerable weight to the boat. It also encourages pools of water to soak through the cover into the boat. Really want to spend 5 hours scrubbing the mold out of your boat in spring? Store your boat with the drain plug out and the trailer slightly elevated at the bow. If you have a stern drive make sure to store it down but make sure you note that it is down. Maybe a bag with your drain plug and a note to raise drive before moving the boat hanging from your trailer tongue as a reminder.