Found this at
http://downeasteryachts.com/info-index/engine/universal-engine-info.
SUBJECT:
Diesel Marine
Engine Antifreeze “Gel” Formation
Many automotive antifreeze products contain high amounts of silicate
designed to protect aluminum
engine parts and aluminum radiators from
corrosion. When antifreeze is not mixed with fresh water in the correct
mixture (1:1), or changed regularly(usually about every 3 years) it can
cause the silicates to drop out rapidly and create a gel condition which can
block the water jackets and heat exchanger… causing severe overheating. The prevention of antifreeze gel formation is to use the correct,
brand-name, regular life (green) antifreeze in the correct mixture with
clean, fresh water, and change it regularly according to the
engine
maintenance manual specifications.
Removing the gel formation from
engine water jackets is difficult. Heat
exchangers and
engine water jackets must be flushed with a caustic solution,
not water.