On the rear of the engine block, upper left is a cover with one end larger (circles) than the other. The Poppet Valve is under the larger cover and the thermostat under the smaller. The thermostat controls engine cooling below 2500 RPM where water pressure forces the poppet to unseat and allow for the extra cooling needed at higher speeds. If the poppet doesn't unseat you will overheat at the higher RPMs and activate the OT alarm. The OT alarm sensor is on the rear of the engine block, down low and has a tan wire exiting it.
The pee comes from the exhaust manifold on the Port (left looking from the rear) side of the block....a rather large flat plate into which a tube is mounted and is the source of the pee stream through a hose exiting on the Starboard side of the engine. Dirt daubers love to plug little holes and the pee output tube is no exception. Trouble shooting that is easy....just disconnect the hose from the adapter on the plate and blow through it...if you can the problem is elsewhere. I never heard of a clogged exhaust plate cooling system but since the plate is right around the corner from the location of the OT sensor its possible one would assume that it could set off the alarm while the poppet is functioning normally.
The engine cooling and exhaust plate cooling are two different systems and the exhaust cover gets cooled as long as the engine is running....obviously since exhaust is hot and that has to be cooled.
You may have a clogged input or output to/from your water pump, since both problems seem to exist.
So, in my troubleshooting agenda, I'd check the hose first. Then remove the poppet and check to see that it works freely. If both those tests pass, then you must have picked up some weeds, or big load of sand operating in shallow water that clogged the water pump. If that's the case you can drop the lower unit and inject water from a hose into the hole in the block where the copper tube sticks that is the output of the water pump to see if you get flow through the block.....the pop off should be removed for this test and expect water to come out of the pee hose adapter on the exhaust cover.
If that all works then I would rig up an electric drill to the drive shaft sticking up.....take a piece of leather and a couple of hose clamps with a hole (saw) drill bit to have a larger surface on the drill, submerging the LU in water up over the water pump height and spin the drive shaft CW. If water comes out of the water pump exhaust tube you are about out of options!!!!!!! Hopefully it won't come to this.
The above is my approach having never done this before but this is how I would address the issue. Other, more learned folks could probably do a better job of finding the problem. Good luck.
