Re: 175 Evinrude Locking up
I am glad you do not have any damage yet. Were those numbers in line with the test you did when purchasing the motor?
But, I really do think it sounds just like a lean lockup type of condition.
The overheat and piston expansion happens very very quickly, because it is sort of a snowball, cascading effect. It seems to take less the 2 seconds for this to occur. The piston heats, expands, and because of more friction, expands more, heats more...etc...etc...and then it's friction finally shuts the engine down. All happening within seconds, maybe two, maybe three.
I have never seen it set off an overheat warning horn, because it happens so fast. It really doesn't even get a chance to heat up the water in the water jacket enough to set off the horn. And just as fast as it overheats, it cools enough to loosen in the cyl, and then is free to start.
It almost always happens at or near WOT, and when it happens you feel a slight decrease in power, and RPM's, then it just shuts down like someone turned the key off. It might turn over immediately when you try to start it, or it may seem like it has a dead battery, and refuse to turn over or turn over slowly. But let it sit for 30 secs or a minute, and it will turn over like nothing was wrong.
I really think that is what you were describing.
I know it is a lot of trouble, but if it were mine, I would do exactly as recommended above, and pull the bypass covers for inspection. Maybe even go as far as pulling the heads for cyl wall inspection.