I just replaced all of the gaskets on my '98 Mercury 25 2 stroke, did a complete water pump job, and replaced the thermostat. In the process, I removed some corrosion from the powerhead at the thermostat housing bolt holes. I had to used a gasket maker in conjunction with the dry gasket to seal the water cover. The motor is pumping water good but now it doesn't open and close like it used to. It is initially closed, opens, and stays open. I don't know why it's doing this now. It doesn't seem to be running hot but, then again, I haven't checked with a temp gun. I just pulled and tested the thermostat in boiling water on the stove and it opened just fine. I took it out, threw it in some luke warm water and it closed fine. Not too worried but just curious. Any thoughts?