My loss of power occurred after running for 45 minutes to an hour at a steady 2800 to 3000 rpm. I think the cooling passages were so rusted in mine that the manifolds could not flow enough water to keep them cool. I finally hired a mercury tech. And we spend over an hour driving around Tampa bay in order to duplicate the problem. Once the loss of power occurred we raised the hatch, hit the risers with the heat gun and the temp was sky high especially on the starboard side, port side temp was slightly lower but still high. Engine temp continued to read around 175ish. I can’t remeber the exact temps as this was three years ago. When I removed the manifolds I saw that the starboard side was significantly more rusted/clogged than port, hence the temp variance. After I replace the exhaust and the problem was cured, you could place your hand on the risers after running for over an hour and it would be warm but not scolding

I have some news. The mechanic ran it with a portable fuel tank connected and issue still occurred. He than hooked up a boat-in-a-box and the issue DID NOT OCCUR (for first time!). When the boat-in-a-box was hooked up they had to open the engine hatch so the hatch had been opened when it worked so they suspected (as wingless had continually suggested) that something is heating up.

They went back to the original boat wiring and ran it first with hatch down and waited for issue to occur. When it occurred they opened the hatch and it cleared it! So we have confirmation that it is a thermal issue as you put it.

I did ask them about the exhaust and risers and they ruled that out. They said that its either a coil or the ECM heating up. They are going to replace the coil first and hopefully it’s not the ECM.

I would have done that myself as far as testing but as far as replacing a coil or possibly the ECM (which I believe has to be reprogrammed) I’d rather have the mechanic do until I figure this stuff out on my own.

Now that we know it’s a thermal issue please let me know if you have any ideas or suggestions.

Thanks,

Scott

Like Parasail asked, how long before it cleared up after they opened the hatch ?

Yes Buy a can of the Freeze-it spray and try the ecm and the coil. See which one reacts.

like right away I believe. Would take a couple of minutes to get it back to 3100 rpm but it worked right after

i just asked the mechanic to confirm and he said not long just a couple of minutes. Is that enough time to cool off? He also said when it happened second time it got worse.