2008 25HP Mercury EFI - Intermittent warning alarm/light.

[08Mirro]

Hello all,

A couple months back, I bought a 2008 Mirrocraft troller w/ a 2008 25HP Fourstroke Mercury on it. I don't know how many hours are on the boat, but the motor looked pristine when I bought it and it still does. The boat actually was in my family for a couple of years prior to me buying it, so I had experience with the boat prior to purchasing it. It was treated with care and used on the weekends mainly. I'm the 3rd owner. I don't have any contact with the original owner, so I cant say how he treated it or maintained it, unfortunately.

As of until recently, I don't recall any issues with the motor. Since buying it, I've run into a warning alarm on two separate occasions. Both occasions occurred when I was coming back into the dock to recover the boat, or when I was idling around waiting for others to finish @ the ramp so I could take the boat out. The warning alarm is continuous. No beeping of any kind. The light is on continuously and the alarm chimes continuously. This has never happened to me yet while under full steam, it's always around idle or very slow speed. This is my first boat but I've done some research and it appears this continuous chime is related to either low oil pressure or engine over-heat. I didn't over-rev or over-speed the engine, so that can't be it so I'm leading towards overheating or low oil pressure, or a faulty sensor regarding those two things. When the alarm comes on, sometimes I can kill the motor and restart it after a couple minutes...and the alarm will not sound again. Other times, I can kill it and restart...and it will come back on. But again, this has never happened at full speed or on plane. And it always occurs AFTER I've been out on the water for a few hours fishing, it's never happened immediately after launching. It's always when I'm headed back in after I've fished for a few hours..but then again, it's only happened on two outings so it's not a huge sample size to draw from.

I've read that a good way of diagnosing the issue is to recreate the problem out on the water or w/ a water flusher in the driveway, and then disconnect the water temp sensor, and the oil pressure switch/sensor. One at a time, to see if either will stop the warning chime. I've found the water temp sensor, but I'm having trouble finding the oil pressure switch. I did find what appears to be a sensor about 4 inches UP from the oil filter, it has a rubber cover on it with a single tan/white wire running into it. It's going directly into the block I think. I'm guessing this is it? Is this where you'd also check for oil pressure using an analog gauge? I don't have one on hand, but I can get one and check oil pressure at idle or low speed.

Also, on the front of the engine, there's a removable plastic cover that's shielding a bunch of wiring for various things. On the back of the panel is a wiring diagram. The diagram lists the oil pressure switch as the brown/white wire. All the wires are secured within this management piece. The thing that confuses me though, the brown/white wire isn't connected to anything. It's just secured there and the connector is covered with a protective cover. Is this a separate hook up for an oil pressure gauge maybe? My boat does not have one currently. Or is it possible a previous owner unhooked something and never put it back? So many questions, being a first time boat owner. I would love to get this fixed. Aside from this warning issue that's occurred twice now, the motor seems to be running in top shape. It starts quickly, predictable and idles smoothly.

PS: Oil and Filter were changed immediately after purchasing the boat a couple months ago w/ quicksilver 25w40 and the proper quicksilver filter. I sort of regret not putting in 10w30 BUT I don't intend on running the boat under 40F and according to Mercury, the 25w40 should be fine for anything above 40F temps. Oil level is dead nuts. Not under filled or over-filled. I put in exactly what it calls for, minus any minor spillage that could've occurred during the change.

PSPS: I can provide pictures if requested. Again, thanks for any help in advance.

 

[08Mirro]

Update: I've managed to diagnose the issue myself. I decided to trouble shoot over-heating as the potential cause first, as the symptoms I had been experiencing seemed more related to over heating than low oil pressure, since the motor starts up and runs fine when cold, but runs into issues after the motor has been in use for a few hours.

I pulled off the lower unit to inspect the water hose first. I've read that in areas where it freezes over the winter, the grommet can sometimes crush and pinch the hose, restricting water flow to the engine. The grommet and hose seemed fine, so I moved further down and took apart the water pump. Here in lied the problem. The impeller was shot, one fin missing and another about to break off. It must have dried out due to the boat sitting for the winter, and in between the time it took for me to re-register it after I purchased it, which wasn't immediate. It was definitely starting to rot out. Anyway, this gave me an "ah-ha" moment, because at times I noticed that the water stream out the back of the engine seemed pretty wimpy at idle and low speed, but would pick up at higher rpm. This makes sense because as the impeller spins faster, it can start to catch up with itself more and make up for the defect, and why the alarm would only go off with the boat at idle or low speed, because it wasn't getting sufficient water flow to cover up for the damaged impeller. Because the impeller was damaged, I decided to take a second look @ the water hose, thinking debris may have lodged in the hose and further restricted water flow. Upon closer inspection, I was right. I was able to snake out one of the impeller fins with a piece of wire. Doesn't appear to be anything else in there, and if there is...it would have to be small and hopefully it will flush out on it's own. I think it's OK though.

As a first time boat owner, I feel a little silly. I should've started looking for a problem the moment I first thought to myself that the water stream seemed a little weak as the motor was in operation. I guess I was just naive and thought this was normal for the motor operating at idle or low rpm. Now I know better. In retrospect, I am glad this issue was related to the water pump and not low oil pressure. It seems like it'd be an easier job to tackle than pulling out the sensor, checking the oil pressure w/ a mechanical gauge, and then trying to diagnose from there. When I pulled the impeller off and saw the damage, I was relieved that I was able to find something so obvious. Apparently this happens a lot with boats that are low hours and sit for long periods. Lessons learned. I'm also going to change the lower unit oil while I've got it off to replace the impeller. Seems like as good 'a time as any to do it. Anyway, even though no one got back to me yet on this post, I thank anyone who may have viewed it regardless. As a new boat owner, this is a very handy forum to have around.