Is the engine in fact getting cooling water? If you are not sure, and if trying to unplug the telltale hose fails, I'd check that all the pipe connections from the impeller up to the block are in place. My Honda 8 (which may of course differ from the Tohatsu) is kind of tricky - it is not that easy to get the two pipes aligned, and if you miss, the water from the pump stays inside the leg and never makes it up to the block.