As part of winterizing my boat this year I have flushed and replace the engine coolant. In fact, I did a flush, then a flush, then a rinse, and then a refill. Will the help of the archives, I managed to sort it out and ensure that the water heater was properly flushed and that there were no air locks. All of the manuals I have and many posts talk about opening 3 petcocks on the engine to drain the old coolant (some talk about 4!). On my engine, I found only 3 drains: - 1 drain with plastic knurled knob on engine block, port side, behind the alternator (when facing the engine). - 1 drain with plastic knurled knob (same as above) on engine block, starboard side, above the secondary fuel filter - 1 drain at the aft bottom corner of the heat exchanger. The drain is metal and has a metal "T" handle. All 3 of the above drains have clear plastic tubing attached. The two plastic drains, when opened, drained coolant. The "T" drain on the heat exchanger, when opened, drained fresh water (not coolant). Since everything I have read talked about all 3 drains needing to be opened for flushing and refilling, I was surprised when fresh water came from the heat exchanger. Is this normal? Are there drains that I have missed, or is the heat exchanger assembled incorrectly? Thanks Chris PS. There are posts in the archives that talk about adding a valve where the water heater hoses attach in order to allow easy burping of the system, and providing a location to force the old coolant/flush from the water heater. Given that I had to remove this hose connection many times during this process, and used an air pump stuffed into the water heater hose to blow the water from the water heater, I think I will install such a valve to facilitate this process in the future.
