Cooling water for small engine !

[olympic]

 

[Steamchick]

I worked in Nissan, both Engine design and QA. Just so I don't break confidentiality I won't explain.... but 50% mix is the best mix for anti-corrosion, even where not needed for -30deg. C. That applies to the mix of metals in the cars, cast iron, copper alloys, aluminium, silver solders, zinc (plating), nickel, (plating), ETC. Don't go higher than 60% glycol as somehow this is worse for corrosion resistance. Or so I learned from the coolant expert in Japan. Use automotive coolant as it does contain lots of anti-corrosion chemicals as well. Youbare paying the premium for their expertise and the anti-corrosion chemical package. So that' s my recommendation. Ordinary "Antifreeze" from your local cheap store probably doesn't have the anti-corrosion chemical package. But the glycol will lower the freezing point, if that's all you need.
Stay safe, Glycol is toxic.