Mercury Mariner 60 hp EFI 2003

by Gil Mac
(Hebrides, Scotland)

I'm getting the overheat/high volt/low oil pressure alarm (long tone) and the engine shudders and slows (goes into limp home mode shutting 2 cylinders down). If I knock off the revs, the tone stops, and I can rev back up for a while. Normally can run at 21 knots at 5000 (Shetland F4). Originally thought it could be the rectifier but I've replaced that. Checked the oil and it was a bit high so I took some out. It's now between min/max. Removed the thermostat and cleaned it out with vinegar (I'm in salt water). Working ok in hot water and free when pressed open. Checked the sensor with a meter and hot water/thermostat to check resistance/temp. correlation. I'm not sure what to try now. I'm worried it's the Mercury grommet issue that I've seem mentioned on a few sites, meaning taking the power head off.Gil

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