Today I got an overspeed alarm at 4400 RPM on one of my 6.2 Horizons. 4400 is the high end of my normal cruising speed. Engines are rated for 5000 at WOT. Was in the 3800 range ad whenever I brought it up to 4400 I would get the alarm. Had to throttle down to idle and come back up. I've gotten that alarm before but only if I rev to high in neutral but never under load. Everything else was normal. Both engines were in synch with the same amount of throttle, same coolant temp, raw water and oil pressure. Engines running fine and boat running normal. Just the alarm. Got it three times in a row.
Engine Overspeed Alarm
- Thread starter MichaelNJ
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- Jul 12, 2007
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- 27413
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It could be a bad sensor, either speed or temp. If temp alarm, it could be a bad water pump impeller, a collapsing hose, or a partially blocked manifold or other part of exhaust/cooling system. You could try unplugging each sensor to see if alarm goes away. You can check cooling system components with a infrared thermometer. Hy
Risers, elbows, water pumps all done last year. My starboard (side with alarm) always reads a few pounds low on water pressure. That sensor is in the oil cooler on the transmission. That oil cooler was also replaced last year. I would not be surprised if it's a sensor issue. I would be surprised if it was any kind of temperature issue. I can run at 4200 RPM with no problem but as soon as I hit 4400 the alarm goes off. I'm tempted to swap the two water pressure sensors and see if the low pressure reading moves to the other engine.
- Joined
- Jul 12, 2007
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- 1,164
Swapping would be the easiest way to check the sensor. Give it a try. hy
- Joined
- Dec 4, 2003
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- 727
I'm getting the same thing and my motor and outdrive are new also, I get no temp reading difference, goes from 174 to 175 thats about it. I blindly cleared my water intake with a screw driver but I doubt that was the issue. I used a heat infrared thermo and everything is under 175. I guess its possible for a newish impeller to break apart..
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- Dec 4, 2003
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- 727
A few years ago after the season I took out the boat out of the water and removed the impeller, it had no panes on it at all, I think the engine was getting water circulation by the engine water pump only, I think because it was already siphon tight is why.
Update: I swapped the pressure senders and no difference. At 3000 RPM I'm getting 7.6 PSI on my port engine but only 5.4 on the starboard. When I removed the sensor from the port engine, there was a significant flow of water coming out of the port. When I removed the starboard sender, no water came out. The oil cooler that it goes into was replaced last year and the port was not blocked. Aside from all this, I noticed that the raw water pump is leaking badly at rest. It doesn't leak when the engine is running so it is probably sucking air. Of course, that the next step and then I'll revisit the pressure and overspeed issues which may go away with the new pump.
- Joined
- Dec 4, 2003
- RO Number
- 12527
- Messages
- 727
So I went into the water and cleared the intake in the outdrive (blindly) with a screw driver. Even though the engine temps 95 on starbord and 145 on port side(using laser thermal gun), and between those two temps everywhere else including the thermostat housing. Now it seems to be running normally, I have gone over 4000rpm and been playing devils advocate by running fast and it has not gone off at all(alarm/limp mode) this boat is a pig, it goes 25mph at 4000rpm and takes a while to get up on plane. Either it worked its way out or the clearing of the intakes helped. Im afraid to really push(WOT) as this is a new motor(100hrs) and I blew the last one.