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Made a trip to pastrick yesterday morning. Ramps all open, docks in, and made it for the freebie. Set lines right outside the harbor mouth and trolled all the way down the wall and past the hole in the wall without a sniff. Water was 37 degrees plus or minus a few tenths, and gin clear.  Was just starting to pick up rods to run to the ship canal when I had a alarm sounding on the 25 mercury. Immediately turned back towards the dock and trolled our way back. Solid alarm, which indicated a possible overheating situation. Water was pumping fine out of the "pee" hole, and nothing felt hot, and the water coming out was cool to tepid. 
At any rate, made it inside the harbor and shut engine down. Let it sit a minute and started back up. No alarm. We went back out into the lake and ran around a little, alarm never came back. Just felt uneasy, so we decided to just load up  and head back home. Talked to a couple boats at the ramp and both indicated fishing had been very slow. I've seen enough reports and pictures to know some guys are certainly finding them, just doesn't seem like they're around inland at the current time. 
Got back home and threw it on the hose for 30 minutes and again, no alarm issues. Water coming out was cool to tepid again. So one of those head scratchers now and leaves that seed of doubt. I'm not terribly mechanically inclined on these things, if any of you guys have a idea, throw it out. Best I came up with doing some "googling" was maybe a thermostat or sensor issue??
Anyway, good luck to all and thank you guys for the reports, even the bad ones, which may be more valuable than the good ones. Looks like a stretch of more late winter type weather coming up, but my first retirement trip sure felt good!!

4 stroke?  Maybe oil pressure?  

yes it is a 4 stroke, and that was the other alarm scenario. I wouldn't know how to check, or what to check for that, and it never came back. I know oil level is good, and oil "looks" new. Last changed in fall of 2019, and used sparingly since, <100 hours. I could change that and the filter out, wouldnt' hurt I reckon

I wish I knew you were out there Mike. I was on a friends boat and we ended up with a nice mix of coho, browns, lakers and a nice steelhead. 

I had a alarm issue with a merc 2005 90horse 2 stroke.. constant alarm, it was a bad low oil sensor. It was a common issue for a few years