On the day of the 2cool tourney, I took my boat out to the jetties...on the way back in, the seaweed was so thick that I couldn't find my way around it, so I just blasted through the mat. A while later, the high temperature alarm sounded and the engine partially shut down. I slowed down (considerably) and idled for a while and the alarm stopped. When I got going, about 10 minutes later, the alarm went off again. Again, slowed down and idled and the alarm stopped. After that, I was able to run the rest of the day without any problems.
I'm assuming that I sucked up some seaweed into the water pump. The indicator stream was strong at all times.
Question...Do I need to get my water pump serviced again? I just had it done about 10 hours ago (beginning of this season).
'05 Merc 115 4 stroke.
Did you tilt the engine up and clear the seaweed off the lower unit? Both times? It didn't suck any into the engine, but once it gets really hot it doesn't take much of an obstruction to make the alalrm sound.
I don't know the answer to you question, but I would not rule out the possiblilty of seaweed getting ingested in the water pump.
About 6 weeks ago I took a certain 2cooler and his dad fishing here in Sabine. We had a plan, but that was just before Memorial weekend when we had those unusually low, almost winter tides. We were in a back lake and decided to fish a shoreline near a cut. Without looking back at my propwash (I know that was stupid) I shut here down. Well, we were on the bottom and this place is too soft to get out and push. I ground down the prop getting us unstuck for about 20 minutes. It sounded the hot alarm just before getting into the cut. I had to take the telltale director thingy off to clear it of shell. Yeah that's right I chewed up shell and passed it through the water passages to the water exit.
So don't rule out the chance of seaweed inside your engine. If you can take the telltale off and you flushed it good, you might be okay though.
I have been having the same problem with my 05 Merc Optimax 115. Please let me know what your mechanic says.
I ran mine down to Baffin, and got the overheat alarm about an hour into the trip. Then I got it every 10 minutes on the way in. I had a constant stream the whole time, even though I normally run it with the jackplate at 2 (my boat runs better with the plate at 2) Took it in, and they pulled the lower unit, said everything looked fine. Told me to run the jackplate all the way down and I should have no problem. Next trip out, I got the alarm again about 15 minutes after launching - with plate all the way down and tucked all the way in. Took it back in, and they said it might have been the impeller, because the computer said that I only had about 6psi of water pressure when it overheated- so they replaced it. I live two hours from where I store my boat, so I havent been able to run it since the new impeller went on.
I even called my manufacturer, and the mechanic said that it sounded like I had a bad impeller. My motor has only 14 hours on it, so you would think that the impeller would still be okay.
If you can, check your water pressure - it should be around ten psi when you are up and running. I will let you know if this fixed my problem when I get a chance to run the boat again.
In the meantime, if you find anything out that might help me I would really appreciate a pm.