At work we have a number of outboards on the trailer boats. We just flush them with straight tap water
. I would imagine that if your tap water has an unusually high amount of calcium carbonate, or an unusually high pH that flushing
with a mild acid like diluted vinegar would be of help in stopping internal scale buildup in the cooling
system. For us, internal scale buildup has never been a problem.
Your right about commercial
products like that. If you can find out what base chemical they use you can make your own solution for a lot less than what you get charged. Quite often all they do is add water to a base ingredient, add a coloring agent and maybe a perfume and then charge a whole lot more than what you can make for yourself.