Honda EB12D Owner's Manual page 30

Coolant Recommendation
Use high quality ethylene glycal antifreeze that is specifically formulated
for use in aluminum engines. Mix the antifreeze with low-mineral drinking
water or distilled water.
A 50/50 mixture of ethylene glycol antifreeze and water is recommended
for most temperature and provides good corrosion protection. A higher
concentration of antifreeze decrease coaling efficiency and is recammend-
ed only if additional protection against freezing is needed. A concentration
of less than 40% antifreeze will not provide proper corrosion protection.
I-1 Th
e use of unsuitable antifreeze, hard water, or sali water will
cause corrosion damage that will shorten the life of the engine.
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