Stupid Haunted Mercruiser Warning Buzzer

[duped]

2000 Merc Horizon 350 MPI inboard. Once last year and now again this past trip I get a constant warning buzzer from my starboard engine. Both times it has happened after running at low RPM while trolling, and only after 2-3 hours of running. As I understand from the manual it is either an oil pressure or temperature alarm. I don't believe the transmissions have any type of warning switch on them, but regardless the fluid is fine on that too. Oil pressure is 40 psi, oil is clean and at the correct level, and temp about 160-165. I have never had any issues overheating, or losing / burning oil or losing pressure. Engine runs GREAT! I did stick my hand on the exhaust manifolds and they were nice and cool. Good water flow out the exhaust. Raw water pump new last summer. Coolant is clean and at the correct level.

To make matters more confusing, I have Fox marine MEFI3 engine gateways, and I pulled up the diagnostics on my phone. While this buzzer was going off, everything is reading normally. As you see in the screen captures below, temp was 161, low oil pressure warning wasn't active, nothing specifically wrong...no red flags.

The only thing the diagnostic says is "General Warning Level 2 active", which is not helpful at all.

Anyway, I shut it down for an hour and used the other engine. When I turned it back on to head in, the buzzer didn't come back on and I had it running at 3300 RPM the whole way in.

Am I correct in thinking that more than likely I have an errant sensor issue more than anything seriously wrong? I think the alarm system uses separate sensors, correct? So in theory a failed temp or oil sensor on the warning circuit could cause this while the sensors the engine computer, and gauges use is fine? I'm struggling for a better explanation at this point.

 

[duped]

Upon another hour of further research I found a few threads that reference General Warning #2 being transmission over-temp and apparently it is a part of the audio alarm, I just didn’t see the temperature switch. Fluid looked fine and doesn’t stink so hopefully it didn’t over heat too severely, but I think I’ll be changing it tomorrow and check the trans cooler while I’m at it. I guess this all makes a little sense, last time it did it, it was a hot summer day. Then it was fine in the fall with the cooler water and air temps and when I launched in the spring. Now the temperatures are heating up and so is my transmission. Not exactly my idea of a great Memorial Day weekend but oh well. I think I may have answered my own question at least!

 

[wingless]

The engine has both a sensor and a switch for both the oil pressure and the water temperature.

On my boat the engine harness used friction push-on cylindrical connectors on the threaded posts for those sensors / switches. Those cylindrical push-on connectors had degraded, causing the alarm to activate.

My solution was to snip off those connectors then crimp on the correct size ring tongue terminals. Those are retained w/ washers and nuts. There has been zero problems for many years after that modification.

 

[duped]

Great idea, I will definitely do that. I hate those connectors. Just went through all kinds of grief with them on my riding lawn mower.

I did change my trans fluid this morning just to be safe. It wasn’t burnt, brown or stinky but certainly a little darker red than the fresh stuff I put in. Who knows how long it’s been. I was gonna buy new alarm switches but just the one for the temp is over $80 so forget that. I’d sooner cut the wires at the buzzer!

 

[scoflaw]

Since these alarms are triggered by a ground path, it would be impossible to complete the connection with a loose wire. The alarm sounds when the connection is made not lost.

 

[wingless]

The engine has both a sensor and a switch for both the oil pressure and the water temperature.

On my boat the engine harness used friction push-on cylindrical connectors on the threaded posts for those sensors / switches. Those cylindrical push-on connectors had degraded, causing the alarm to activate.

My solution was to snip off those connectors then crimp on the correct size ring tongue terminals. Those are retained w/ washers and nuts. There has been zero problems for many years after that modification.

Since these alarms are triggered by a ground path, it would be impossible to complete the connection with a loose wire. The alarm sounds when the connection is made not lost.

That makes sense and is fine.

Mine had intermittent identical alarm symptoms w/ perfect oil pressure and water temperature until I swapped from the push-on barrel connectors to the ring tongue retained by a nut connectors.

The problem never returned after that change.