11. The engine temp goes way up and then falls back down over and over. I have replaced the thermostat three different times, and it still does the same thing. It seems to be the worst when I am motor sailing so the load is the least.

You might try putting a little more restriction in the bypass loop. This is the hose running from the "T" fitting in the middle of the water jacket side plate to the inlet of the thermostat housing.

You could try simply crushing the hose a bit using a pair of visegrips to see if it helps. If it does, you could plumb a small ball valve in that loop for a more permanent fix. - Updated: November 4, 2003