Merc Motor Alarm?

Lent my boat to a friend fishing up at Lake Kabetogama and he called and said the motor alarm keep going off when he is reverse trolling. The motor is a 1999 four stroke Merc, tiller on a 16.5′ lund angler. He said it was cirulating water okay. Any Ideas????? I never had any troubles with is unless you plug the intake with weeds.

oil?

He’s pretty savy with mechanical stuff so I doubt it’s oil level. Suppose if the oil pump was going bad… are there any other reasons an alarm would beep other than overheating?

My 75hp 2 stroke Merc did something similar to that. The alarm started going off constantly. It was peeing water and had oil in the oil tank. I took it to the Merc dealer in Red Wing and they determined that it was the low oil sensor. I am not sure how common this is, but they diagnosed the problem in just a couple minutes.

I have a ’99 Merc 50hp four stroke. Mine also alarmed at trolling speeds, looked like it was circulating water as well, alarm went away at higher rpm. Turned out to be the impellar. Replaced, no problem since.

get it checked for sure. Could be an oil pump. Could be the sensor.

Thanks everyone. I’ll have to pray (until I can get it checked) it’s a faulty sensor, because it only goes off at very low rpms, pees fine and never acts hot.

My $.02:
Pretty sure the water pump (impeller) needs replacement. If it has never been replaced, it needs it. The engine may not feel hot, but the sensor is picking up the core temp. At idle there is not enough water pumped to the powerhead at low RPMs. It will still “pee” water just fine making you think there isn’t an issue.

I replace the impeller every 3 years on my big motor.

My 05 optimax started the same thing this winter when we went to Texas.Got it fixed when we got home.Water impeller was wearing out.The repairman said to plan on switching them out every 3-4 years depending on usage.Works fine now.

DOES THIS MOTOR HAVE A WATER SEPERATOR UNIT ON ITS FUEL LINE. I PICKED UP SOME BAD FUEL ONCE AND THE ALARM WENT OFF WHEN THE WATER SEPERATOR CAN IS TOO FULL. GO TO YOUR MERC DEALER AN HAVE IT CHECKED OUT BY A PROFESSIONAL.