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My 40 HP 2-Stroke Mercury monster started complaining to me for the first time ever yesterday. Motored for about an hour to get out in the Mississippi Gulf. Great winds, great sailing...no dolphins unfortunately (my daughter was dissappointed). But we had great sailing for about 3 hours. Then I started the motor to head back to the marina. After about 2-3 minutes at low RPM while lowering the sails the warning horn went off.

I suspected low oil as I forgot to top it off. Sure enough the oil reservoir looked low so I poured in a quart. Restarted, horn went out...hoo-ray Jim is a "Super Genius"...

Hold on there Mr. Genius...the horn came back on after about 30 seconds...Dohhhhh

Looked in the manual. Either overheat or low oil. The engine was "pee-ing" just fine and the water didn't feel hot at all. And I had just put oil in. The horn stayed on for the next hour all the way back to the marina. But the engine worked just fine all the way back...normal RPMs (5300 at WOT) and normal speeds (16-17 MPH with no ballast, two people, and against slight headwind).

I took the engine cover off and the motor felt fairly hot...but I have never tested the temperature underneath the cover before so I am not sure if this was unusually hot or just the normal temp after running the engine for over an hour. But nothing looked wrong (but would I even know???) And as I said the water pump was working fine and that water didn't feel too hot to me. And I think the engine was maybe just a little bit "smokier" than normal...but not sure about this...could have been my paranoia as I was closely monitoring the engine all the way back.

I am hoping that the motor will "reset" itself after being completely cooled. And if it works properly today I will pay attention to the temperature under the hood and the level of smoke.

Any thoughts from those of you more mechanically inclined than I...which would probably be over 90% of the members of this distinguished board...

Thanks,
Jim

Hello,
I hesitate to give advice but...............There is a possibility that the oil level switch is malfunctioning. You might want to check it's action. If the condition returns, try unplugging the oil level sensor to see if it stops the warning. Engine overheat sensor is a bi-metal snap switch screwed into the head somewhere. If it gets rusty inside it can give a false signal, something that has to be replaced. Try unplugging it when the warning is sounding. The motor also has a thermostat so it is possible to have water peeing, a good pump and still have a hot motor so you need to check the actual operating temperature.

I don't have a Merc myself, but my understanding is that an overheat signal is steady vs. low oil is repetitive beeps. Wouldn't hurt to check the senders of both.

Gents,

Thanks for the advice. I took her out again today. Cranked up...no warning horn. Motored out of the marina at 2000 rpm, turned into the wind to raise the sails...and the horn came on again... Never even got above 2500 rpm and the engine hadn't been running for very long.

It is a steady tone...very annoying tone. I got the sails up and turned off the motor but since I didn't have full confidence in it I only sailed back and forth near the marina in the Biloxi Bay...never more than about 1 mile from the marina. The winds were blowing pretty good and I could have had a blast sailing out of the bay and into the Gulf...but I would have had to motor an hour back against the wind. Couldn't take the chance.

So after about an hour of back and forth sailing in the narrow channel, I lowered the sails and motored back to the marina...with the horn again...but the motor seemed to be working fine.

I suspect overheat...the engine does seem warm...but the water shooting out of it doesn't feel hot.

My Christmas Sailing adventure has ended... I de-rigged the boat and prepared it for loading on the trailer as much as I could. I got the main and boom off and stowed. Got all the lines off and stowed. Only the Genoa on the furler covered with the sock and the topping lift (which I will remove when the mast comes down) are left. The trailer is in the shop getting welded and should be ready tomorrow before lunch so I will load up the boat tomorrow or maybe wait until Wednesday.

I will trailer the boat back to Jacksonville, FL on Saturday and then park it in storage until this summer. Then when I move back to the U.S. I will fly down to Jax and pick up the boat and my truck and trailer it to wherever I move to. And then I will try and find these oil and temp sensors and play with them and if that doesn't solve the problem I will try to find a Mercury Maintenace Shop.

Thanks,
Jim

How many hours does your motor have on it ?? There is an alarm that goes off when it needs an oil change . Mine goes off every 100 hours of use and needs reset after each oil change. I would ask a dealer for your type of motor and for the reset .

Many hours...not sure how many. But it is a 2-stroke...no oil change...just lower-unit lube.

And I looked up the warning horn...it states it only goes off for overheat or low-oil in the reservoir.

Jim

Jim - a normally operating engine will be hot under the cover - hot enough to burn your hand in some places. I agree that if the pee stream isnt hot, the thermostat would be the next thing to suspect.

I dont know a lot about 2 strokes, but I doubt your engine would run for hours with a major oil issue - almost certainly a bad sensor.

Merc does have a digitial interface that the dealer can connect to and download error codes.... might be a good thing to have done.

Glad you got some sailing done - have a safe trip back overseas.

And kudos to your command decision, CAPTAIN, about playing it safe behind the breakwater. No doubt professional training took over that judgment call.