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2002 – 4 stroke Merc/Yamaha 115 alarm sensor keeps going off.

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Epper57

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2002 – 4 stroke Merc/Yamaha 115 alarm sensor keeps going off. This is a Mercury engine but it is my understanding that Mercury did not make a 4 stroke in 2002 so they contracted out to Yamaha. When plugged in it runs on Yamaha computer software.

The alarm sensor keeps going off and I have tried everything I can think of so looking for suggestions. (Should probably mention that the motor is run in salt water and has about 700 hours on it. Flushed and maintained on a regular basis.)

Have changed the thermostat, the alarm sensor, pulled the leg and changed the impeller and all the gaskets. Changed the gasket on the water jackets. Drained the oil and then put it back in as things looked fine. Boat is peeing out well (better than it used to).

The last two times I have put it in the water the alarm sensor has gone off instantly (when the motor is cold). Once the alarm has stopped it will run for about 4 minutes and the alarm goes off again. The thermostat seems to be working as there is a noticeable drop in the amount of water coming out of the tell tale once it reaches temperature.

Again the last two times I have been out, once the sensor has gone off for a second time, I unplug the sensor, let it sit for a minute, and then plug it back in. It has then been run for 20 minutes (first time out) and over 30 minutes (second time out) without the sensor going off. Temperature normally ran between 160 and 190, although we did get it up to almost 200 at 5400 rpm without the sensor going off. Then shut off the motor and left it for about 10 minutes, started it back up and ran it for about 4 minutes and guess what – sensor went off again.

Motor does seem to have more exhaust then it used to coming out the vent hole. Could be the weather (?) as it is late October.

Suggestions?
 
I assume by "sensor" you mean the thermosensor (aka thermoswitch, aka cooling water temperature sensor). There's also an oil pressure switch that will trigger the buzzer. The neutral switch will also trigger it, but it wouldn't allow you to start the engine in that case.

If the buzzer sounds instantly when the motor is cold, that means you at least have an electrical issue. However it does seem like you're overheating if it's reaching 200F at high speed. Treat these as separate issues, and you'll figure it out. I would address the overheating first.

When the engine is warmed up and you increase the idle speed in neutral, does the water exit stream get stronger? Or does it still appear weak at that time? If it's still weak then, I would rebuild the water pump as a first step (they sell a repair kit for about $45). While the lower unit is removed, make sure there's no blockages in the water tube that goes up into the fuel cooler. From there, check for blockages in the water exit passageway.

Basically, I wouldn't do further troubleshooting until you get the temp down below 190F at all times. Then worry about fixing the electrical issue with the sensor triggering the buzzer when it shouldn't be.
 
Did you service the water pressure control valve?

PN 6G5-12416-00-00

The pisser stream should stay the same. If this is stuck slightly open the engine will overheat.
 
Hello, did you ever figure this out? I'm having the exact same issue.

Thanks,

John

Epper57 said:
2002 – 4 stroke Merc/Yamaha 115 alarm sensor keeps going off. This is a Mercury engine but it is my understanding that Mercury did not make a 4 stroke in 2002 so they contracted out to Yamaha. When plugged in it runs on Yamaha computer software.

The alarm sensor keeps going off and I have tried everything I can think of so looking for suggestions. (Should probably mention that the motor is run in salt water and has about 700 hours on it. Flushed and maintained on a regular basis.)

Have changed the thermostat, the alarm sensor, pulled the leg and changed the impeller and all the gaskets. Changed the gasket on the water jackets. Drained the oil and then put it back in as things looked fine. Boat is peeing out well (better than it used to).

The last two times I have put it in the water the alarm sensor has gone off instantly (when the motor is cold). Once the alarm has stopped it will run for about 4 minutes and the alarm goes off again. The thermostat seems to be working as there is a noticeable drop in the amount of water coming out of the tell tale once it reaches temperature.

Again the last two times I have been out, once the sensor has gone off for a second time, I unplug the sensor, let it sit for a minute, and then plug it back in. It has then been run for 20 minutes (first time out) and over 30 minutes (second time out) without the sensor going off. Temperature normally ran between 160 and 190, although we did get it up to almost 200 at 5400 rpm without the sensor going off. Then shut off the motor and left it for about 10 minutes, started it back up and ran it for about 4 minutes and guess what – sensor went off again.

Motor does seem to have more exhaust then it used to coming out the vent hole. Could be the weather (?) as it is late October.

Suggestions?
Click to expand...
 
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