It's spring cleaning time and I am about to change the fresh water in my Yanmar. I have done this plenty of times on auto's and it seems straight forward, but I am just asking if there is anything that I should be concerned with. I thought I read once in this forum that you could get an air lock on the cooling system but that seems like it would be more likely on the seawater heat exchanger. I plan to change the impeller and I thought I would use a 50/50 mix of anti-freeze(automobile prestone) and drinking water. The anti-freeze is mainly for the rust inhibitor. Any thoughts, experiences, alternative suggestions are apprecitaed.