Since then, we've replaced the water pump (impeller), and the thermostats, but the heating continues.
We are ok if we are at higher RPMs and speed, but when we slow to anchor, it heats up quick.
Our next idea was a stuck Poppet valve - if it was stuck open it wouldn't build water pressure.
There are great diagrams and information on outboards at this site: http://www.boats.net/parts/search/Merc2/Mariner/V-200%20(2.5L)%201991%20ONLY/parts.html
The hardest part of openning up the Poppet valve was removing the lower Cowling.
We found the first 3 bolts easily, and finally found the last one up front of the cowling.
The poppet is on the lower starboard side (right) of the motor.
Outboards are pretty easy to work on - it is nice they are easily available to get at most of the parts...
Here you can see the poppet housing.
It has been a while since anyones been in here.
The gaskets were in good shape, and some grit and sand inside.
Actually, I was really hoping to find alot of sand and gravel - so then I'd be more confident this would fix the overheating problem.
It looks too clean inside...
We flushed the motor with a hose up at one of the thermostat ports, to blow out any gravel inside to come out the valve.
We scrubbed and cleaned it all up, and it went together very easily. W
Now lets keep our fingers crossed that it fixes the problem.