25HP overheat alarm and running rough

[Skidoonick]

Hi all,

Bought a used pontoon this spring which has a 2002 Yamaha T25TLRA 4 stroke. Ran great for multiple trips/ hours then one day on our way back in this alarm is going off and engine is running rough (rpm limiter im guessing / limp mode) I had zero clue at the time what the alarm was and we proceeded to run the engine for another 5 minutes at least as we made it to shore to beach it. Discovered it wasn't peeing. No blockage in telltale.

Fast forward a couple weeks I put in a new impeller and it now has a nice strong stream of water. Also did an oil change because she got HOT when it overheated. We lauched it in the water and putz through a No Wake zone which took 5 minutes or so. No alarms, telltale peeing great. Go to throttle up and soon as I get past 20% throttle it starts shaking and running rough, sort of like it's in limp mode. NO alarm.

We go to beach it. Check spark plugs, wiring, anything else that we could easily do. Started it up and revved it in neutral, it revs up just fine no issue. All of a sudden alarm goes off (constant tone) and limp mode / rpm limiter is back again. Turn it off. Pulled out thermostat and checked for any blockage. Ran motor without tstat. Over heat alarm within minutes. Water coming out of telltale not hot, just a little bit warmish. Engine doesn't really seem all that hot, certainly not as hot as when it overheated and wasn't peeing.

I'm not sure where to go next and don't have much knowledge of outboards. Don't know the history to it either. About ready to call a mechanic.

Any suggestions of something I could try before paying someone?

[panasonic]

Was the old impeller in pieces? If so, where are those pieces gone?

[Skidoonick]

Not really. Mostly what happened is the woodruff key got dislodged and I guess that led to the impeller no longer spinning. Pictures attached of old impeller it didn't look that bad to me but as I said I'm new to all this so who knows.

Maybe there is a small piece lodged in the cooling passages somewhere? I wouldn't know where to look lol.

[panasonic]

Well it's good it never went to pieces. I would go back and make sure all is well with the water pump.. Did you replace the impeller as a kit or just the impeller.? The old one looks like it started to melt so it must of got hot..ran dry. Just because its peeing doesn't mean the water is flowing at the proper rate to cool the engine. You could pull the thermostat cover and run the engine briefly to see if the water is making it up there.

[Skidoonick]

Well it's good it never went to pieces. I would go back and make sure all is well with the water pump.. Did you replace the impeller as a kit or just the impeller.? The old one looks like it started to melt so it must of got hot..ran dry. Just because its peeing doesn't mean the water is flowing at the proper rate to cool the engine. You could pull the thermostat cover and run the engine briefly to see if the water is making it up there.

I replaced it as a kit that yamaha sells minus a new housing. I may have caused some damage to the impeller, or the previous owner. I've had this habit of always starting it dry on the trailer and sitting off immediately just so I know all is good before traveling to the launch. I'm not sure if that couple seconds can burn one up. My uncle advised I stop doing that when I installed the new one.

I'll give your suggestion a try regarding the tstat.

[Skidoonick]

Well it's good it never went to pieces. I would go back and make sure all is well with the water pump.. Did you replace the impeller as a kit or just the impeller.? The old one looks like it started to melt so it must of got hot..ran dry. Just because its peeing doesn't mean the water is flowing at the proper rate to cool the engine. You could pull the thermostat cover and run the engine briefly to see if the water is making it up there.

Well I ran it with the thermostat out for a brief moment, water pouring out so water definitely is getting past the thermostat. Overheat alarm came on in about 4 minutes. (I put the tstat back in and cover on and restarted for the 4 mins). Was revving the engine a couple times during that 4 minutes and it runs rough past about that 20% throttle point.

I'm going to be getting it looked at by a mechanic at this point.