This preparation needs to be done prior to removing water from the engine if that will be part of the process. Boats that are going to be stored for extended periods (more than two  weeks) or winterized should have the fuel system treated with a stabilizer. Even TOP TIER gasolines will experience some separation and settling during these periods. Of considerable concern is that water condensation will occur within the fuel system. Water is particularly harmful to fuel tanks and engines, therefore, follow this procedure:
CAUTION: Winterization is a complex process that may result in damage to the engine, drive train and other components if improperly performed. MasterCraft recommends winterization by an authorized MasterCraft dealer.
Before starting you will need the following supplies:
- Sta-Bil® Gasoline Stabilizer
- Fuel filter
- Low tack tape
The fuel tank should be ninety-to-ninety-five percent (90-95%) full of TOP TIER gasoline. This allows for minimal room in which air can oxygenate the fuel during diurnal cycles (daily periods of expansion/ contraction of gasoline vapors and air as a result of temperature changes).
Add a biocide additive in the fuel tank to limit microbial growth in the gasoline. Follow the directions provided by the additives manufacturer.
Add a fuel stabilizer, such as Sta-Bil® (preferably the Marine grade or Ethanol grade stabilizer) to the fuel tank. Follow the directions provided by the stabilizers manufacturer.
Run the engine for at least fifteen (15) minutes while in a body of water. This allows for the circulation of the additives throughout the fuel system.
During storage, the tank vents can be sealed. If the vent is sealed, the tank must NOT be completely filled. A ninety-to-ninety-five per- cent (90-95%) filled tank allows room for expansion, which will be required at certain times when temperatures increase. In addition to preventing water intrusion, sealing can prevent the gumming that occurs when the hydrocarbons in gasoline react with naturally occurring oxygen. This gummy substance plugs up fuel filters and injectors. Sealing the tank helps reduce gumming by significantly limiting the amount of oxygen that is allowed into the fuel tank. If the tank vent is sealed for storage/winterization, it must be unsealed prior to the boat being placed back into service. Failure to do so will result in issues when trying to fill the gas tank in future fill-ups.
Note: Fuel stabilizers work ONLY in fresh gasoline. Stabilizers will not cure oxygenated gasoline. Adding a stabilizer when the boat is being prepared for outings after storage will NOT clean the gumming that has occurred or remove water from the fuel tank or otherwise eliminate any problems that have occurred due to failure to properly prepare the fueling system for storage.
Engine manufacturers suggest using Federal or State of California reformulated gasoline whenever possible as it stores as well or better than conventional gasoline.
Even quality gasoline that has been properly prepared for storage should never be stored for a period to exceed one (1) year.
CAUTION: Fuel systems on all boats MUST be properly prepared for storage periods exceeding two (2) weeks, as outlined in this Owners Manual. Failure to do so may void the warranty.