Extended Life Coolant
Make sure you you use the recomended extended life coolant. You can't use Prestone or any other car type coolant, but you can find the extended life in most auto parts stores, Cheveron and Texaco extended life or long life coolant are what my mechanic told me to look for. I bought the premixed 50/50. My mechanic told me to drain the system then fill with water run it on a weekend trip then drain again and fill with the premix coolant. I also had to replace the plastic drain cocks, Yanmar has redesigned the cocks and made them brass, the plastic just doesn't do well. I noticed a pool of coolant in the bildge, the mechanic told me it was the old style cocks, he ordered up the new cocks. I also had to remove the fuel pump and replace the gasket, which was around a $1.00.