I was sitting on the back of the boat having a couple "sodas" last weekend with my buddy Dan, he left, I was messing around in the cabin, and the port motor started sounding different. Not bad, not knocking, not even a hot oil lifter tick (motors just sound different when they're running hot), it just didn't have the same sound or frequency to it. So, I went to the helm and the temp gauge was reading 220+ (I didn't get a good look, it wasn't pinned, but it was hot). I immediately shut it down and opened the hatch, damn antifreeze everywhere - couple gallons at least, and the reservoir was empty. I checked it over pretty good, but it was around 2am, dark and I didn't want to mess with it while it was hot, so I buttoned it up, and went home. I figured that I would see the worst of it when I got down to the boat the next morning, but... Nothing...

It was still obviously out of coolant, but no visible signs of where the coolant leaked from. I checked it over real good, no water in the oil, no visible cracks, no blown hoses. I added about a gallon of water, and fired it back up, and it ran great. It did get hot (180) after running for 35-40 min, but that was somewhat to be expected, I didn't top off the coolant, and I didn't bleed the system. However, the boat had no visible signs of a leak, crack or blown hose... I don't get it? No water in the oil, no smoke in the exhaust, nothing. The little bit of water that was left in the reservoir was rusty colored, but not oily. Not sure what could have happened.

It was pretty hot that day, and the lake temp is up at the end of the year. Is there some sort of blowoff valve, or pressure relief valve that could have opened up? The seaweed growth is up a ton too, I'm wondering if my pickups to the freshwater side are clogged, but that wouldn't explain the puked antifreeze all over the bilge. Thoughts?