Vet inte hur kul det är, men så här står det i manualen till vår Beta 25. (Volvo Penta D1-30 har en liknande beskrivning.)
For cold climates where the air or water temperatures can fall below 3°C, the sea water circuit must be protected in addition to the fresh water system. This is best achieved as follows:
Close the inlet seacock to the engine (engine stopped).
Disconnect the sea water inlet pipe and dip it into a small bucket containing 50/50 anti-freeze solution.
Start the engine (out of gear) and run for 5 to 10 seconds until the anti-freeze is used up and can be seen coming out of the exhaust outlet.
Shut engine off and reconnect the inlet pipe to the seacock.
The sea water or raw water circuit is now protected by anti-freeze.
Mackey