Fall Engine Maintenance

Information on this page primarily refers to 4 cycle gasoline fueled inboard and I/O marine engines

Since most areas of the country will be experiencing freezing temperatures during the coming winter and boats will be in storage, your boat must be properly prepared.

Before storage, oil should be changed in all inboard and I/O engines with oil meeting your engine manufacturer's specs. Most recommend premium straight 30 or 40 weight oils for their
gasoline engines depending on the temperatures the engine will be exposed to when running. Be sure to change your oil filters also. With diesel engines it is also a good idea to change your fuel filters to prevent any water from sitting in the injectors or pump during the winter. If your boat has not been run much during the summer, it would be a good idea to add fuel stabilizer to the fuel system to prevent gum and varnish in the fuel system. Holding tanks must be pumped out and antifreeze added, water systems drained and filled with non-toxic antifreeze, and all personal items removed from boat that might freeze and cause damage over the winter.

Engines with closed cooling should have the antifreeze mixture in the cooling system checked and antifreeze added to assure protection at the lowest possible temperature for your area. Antifreeze should be changed at least every two years to prevent corrosion.

After changing oil, filters, adding antifreeze to cooling systems, the boat should be run to distribute fresh oil to all components, circulate coolant, and bring any fuel additives into the fuel system. After the run, recheck all fluid levels. and including closed coolant after it has circulated to make sure your antifreeze is strong enough.

Gear cases of outdrives and outboards should be checked for excessive water. A large amount of water can freeze and break, destroying the housing. If you notice a lot of water in your lower unit, drain it now and have it resealed over the winter by an authorized dealer for your particular
model unit.

If you have an outdrives, try to store it in the down position if possible. this prevents the boots from taking a set and also promotes good drainage of the unit. If you cannot keep your unit in the full down position because of your trailer, lower it as much as possible without touching the ground. Just remember to put it up before you move the boat in the spring!

Make sure all hull plugs are out so that water will not accumulate in the boat causing damage to engine and interior. Please be aware that permanent antifreeze cannot be discharged into lakes and rivers, so that it cannot be used to fill your raw water cooling system! Your engine must be drained, or filled with non-toxic marine engine antifreeze only. Many amateur mechanics are still using permanent, but this practice is Illegal.


I will not get into a step-by-step procedure for winterizing your engines due to the many different configurations of cooling systems in the field at this time. Unless you are COMPLETELY familiar with your engine and drive system, which in this case, you do not need any help, we recommend you have it winterized by a PROFESSIONAL MARINE SERVICE ORGANIZATION. Part of what you pay for is the insurance that if there is a problem relating to winterization, it will be taken care of. Beware of fly-by-night so called mechanics that work out of the back of vans that carry no insurance and may not be around in the spring when you find that you do have a problem.

Batteries should be disconnected and charged several times during storage. Constant trickle charging is not recommended, as it will boil the water out and damage the batteries. Any batteries over 3-4 years old should be replaced in the spring since batteries used in marine service usually are no longer reliable after that length of time.