Here's what you have to do to get your engine ready for the winter:
1. Gasoline: If you have a stern drive craft or cabin cruiser it's highly unlikely that you will run the craft until it is out of gasoline and it is equally as unlikely tht you will put a neutral, non-flammable gas into your gasoline system, now emptied, supposedly, to keep a positive pressure on all of the pieces so that you wouldn't face the burden of having a trained mechanic replace all the key belts and hoses next spring (notice the changes have made all but the most rudimentary items you can to do a marine engine just about impossible. So, what's the solution? The answer is easy, there are many gasoline stabilizing compounds out there that you merely have to measure correctly and then run your engine for several minutes as the stablizer reaches all parts of the engine. When it does, you're all set.
2. Hoses and belts: Although engines are pretty much sealed, it doesn't mean you cannot have your marine mechanic ensure that the hoses are in good shape -- not mushy or leaking -- and that the belts are in good shape -- not shiny from slipping.
If your mechanic finds a specific belt that needs replacing and all of the others are in good condition then all you have to do is replace that particular hose or belt. Make sure that is all you are charged for on the service bill by making sure they return the parts they replace to you.
If the hose is leaking then it's a good idea to change the anti-freeze/coolant (yes, it's just like a car engine only smaller and marine) in a 50/50 ratio of anti-freeze/coolant to water. This should ensure your boats block won't freeze up at 10 below which would happen if you used the wrong formulation.
3. If your boat's battery is more than three years old in the environment in which it works -- salt water, storms and who knows what else -- that's about the maximum to go before you have a stress test performed on it. It's likely that the battery will test out fine because today's battery is a sealed affair and can easily last 60 or 72 months. Still, a check, and if you want to be on the safe side, change at this time, is always a good diea.
4. If your gas filter or air filter hasn't been checked in a couple of years, it's advisable to check them out. Anchoring near beaches is asking for trouble when you start your engine in the morning as not only is the engine sucking in vital air, it is also sucking in any particulate matter that is also out there so if there's fine sand out there, it's possible that not only will you find it getting into your fueling system, but also into your air filter. So it pays to have these filters checked two.
5. Make sure all of the electrical connections you can see and work on are tarnish free and clean before you close them up. It's a good idea to use a coating of fusable tape (it adhere to itself and makes a heat-shrink-like bond with the device. A coating of RTV or liquid rubber to protect it further from the weather would be a bad idea.
6. If you trailer your vehicle, it's a good idea to not only store your vehicle off the trailer as on a boatyard's storage shelving, but at home it's a good idea to spray down the chains and hitch itself. It would also be a good idea to take your trailer's tires, let the air out and store them on their sides on a wooden box so that dry rot won't develop. Be sure, that this won't happen by applying a protectant sealer such as ArmorAll.
Though this list is by far not the most complete you will find out here, it is also a practical one based on the realities of EPA rulings and such. Try it and you'll have your boat running the first time you put it into the water next spring.