Marine Insurance claims statistics contain many stories of engines that froze and failed after skippers failed to prepare the engine for winter properly. Generally, engine blocks that freeze and crack are not covered by a boat’s insurance policy.
Papering the engine for winter is one job that is truly critical; follow the steps below and consult your manual for specifics.
Oil and Fuel Systems: Petrol and Diesel
Step 1: Change the Oil. Residual acids and moisture left in the crankcase over the winter will pit bearings and other vital engine parts, so it is important to change the oil just before laying up the boat. For best results, run the engine for a few minutes to lower the oil´s viscosity. Shut off the engine, change the oil, and replace the filter. Rubbing oil on the filter´s gasket will help it seat better.
Restart the engine and run for about a minute to circulate the fresh oil to internal parts. While it´s running, check to make sure the oil filter isn´t leaking.
Step 2: Replace the Fuel Filters. Replace the fuel filter and change the fuel filter canisters. Like the oil filter, the fuel filter should be checked for leaks while the engine is still running.
Because there is no carburettor or ignition system diesel engines winter over better than petrol engine. At the same time, there is more at risk to the ravages of rust and corrosion. Beside being a very expensive to rebuild or replace, a diesel has components that require professional, factory-trained service people to work on such as the high pressure fuel pump, fuel injectors, and on many modern engines, a turbo charger. The fuel system on a diesel is also very critical and demands an extra degree of attention.
Small Sailboat Diesels
Change oil, transmission fluid, and filters. Drain and clean all fuel filters. Replace fuel elements and gaskets. Bleed all air from the fuel system. DO NOT use the starter to turn the engine while pouring the oil or serious engine damage could result. Tape the openings of the intake and exhaust manifolds to keep moisture out of the cylinders.
For large diesels, fogging the engine or squirting oil in the cylinders should NOT be attempted unless specifically recommended by the manufacturer. It is usually preferred to drain the raw-water system rather than filling with anti-freeze. Be sure to drain from all low points. Remove the water pump cover and impeller. The blade of the impeller bent against the pump housing may take a set during storage.
Source: USBoat world.