Not a problem
with an air lock. Coolant should be changed every two years in an automobile. The Yanmar manual replacement interval for fresh water is 1,000 hrs. I did mine this past Spring and though I doubt it has 1,000 hours on the engine, I feel it was a very good service. My boat is an 89 Hunter30 and I doubt the coolant had every been changed. I placed the drain tubes in a pop bottle and as it filled, transfered the old coolant into an empty gallon jug. Make a 50/50 mixture of a high quality antifreeze and distilled water. The system will bleed itself out - just be sure to check the overflow tank level regularly to be sure it is between the low and full marks. Have fun! -Doug
