What is the correct type of antifreeze to use in cast iron marine engines with copper heat exchangers?
Unless the marine engine is made of aluminum low-silicate antifreeze should be used. In newer automotive engines with aluminum components and radiators silicates are added to the antifreeze to protect them from corrosion by dropping out at a controlled rate. Marine engines made from cast iron and fitted with copper heat exchangers do not need silicates in the antifreeze, and if silicate anti-freeze is used the silicates may “drop” unexpectedly to create a soupy mixture which will eventually harden and block water passages. Removing the silicate is difficult because it is not water soluble and usually must be removed by chipping it out or sending the components out for cleaning in an industrial caustic solution.
