BobPaul and Bubba, My Merc gets high temp alarm on many trips onto the Mississippi River. I can go 2-3 miles at about 4000 rpm and the continuous alarm goes off. I throttle down to an idle and it clears up after a short period. The telltale pees pretty strong at idle and blasts out with higher throttle settings. The first couple of times it happened I assumed I got silt into cooling system and used the hose connection at the back of the motor and flushed it. The next time (until recently) never overtemped. Now, even after the hose out, I will normally get the alarm. Yesterday, I went out @ 4000 and got alarm. It cleared after idling and we fished. On the way back I went a little faster ~5000 and got no alarm. I had impeller replaced last year but the river at times is somewhat silty. The shop removed the thermostats at the same time. What do you think? Impeller, sensor, either, other mechanical problem possibilities? Thanks.