As long as you shut her down went the alarm went off, I think you should be OK. A few things sound a little funny to me though about your problem. Were you drawing water out of a bucket while running, or was the garden hose connected directly to the cooling hose in the boat? I always connect directly to the hose on the pick-up side of the water strainer. In this case, an air leak would not have caused your problem as the pressure from the hose would have been pushing water through your system. I am not familiar with the Black Scorpion engine, but on every marine cooling system I have worked on, water is always flowing through the exhaust, regardless of the thermostat. The stat allows water into the block when it opens, when closed all the water flows out through the exhaust. In other words, the hose going to the front our your manifold should have water in it at all times. Also, for future reference, if you follow that hose from the manifold up, the other end should be somewhere very near the t-stat housing.
I hope it is fixed, but I would keep an eye on those manifolds and risers. They should never get so hot that they would burn your hand with a quick touch (actually you should be able to lay your hand on them for several seconds, again, not familiar with a Scorpion engine, but I am assuming the same holds true).
Last edited by azeus17; 05-24-2012 at 8:20 AM.
Reason: clarify garden hose