You didn't use my trick to thaw the hole? You remember. I think I had to go dumpster diving to get a piece of wire off from the back seat of an 87 Astro van. Heat, insert, repeat!

When fishing in cold conditions, as soon as you get back to the launch and pull the boat out, lower the motor all the way down. Unscrew the flush plug. The location where you hook a garden hose to your motor. This will relieve back pressure and allow all of the remaining water above the waterpump to purge out of the hole. You could also blow in the flush plug to purge the water faster. I've been meaning to produce something that screws in to the plug and connects to a can of "canned air" but have yet to do so. I look like a fool at the launch but I don't get freeze up anymore. I'll bet that water was in there from the last time you went!