[snmcharters]

I have a 2000 Yamaha 115 2 stroke and I've been getting an overheat alarm at high RPMout goes off when I pull it back to idle. I talked to a friend who told me it might be the impeller but I am doubtful because it is still pissing well and the water coming out is still cool even when the alarm goes off. Any ideas.

[pine island fred]

Yes, time for a water pump. When you get the kit be sure to get the small plastic insert and stainless collar that go on the shaft. Unless things have changed, they are not included in the kit and chances are you will need them. FRED

[cousinabe]

are you sure it's an overheat alarm and not an oil transfer alarm.
what indicators/lights are flashing on the gauge?

overheat could be clogged thermostats or clogged up prv(popit valve).

[EAVES]

That engine on the botttom between the heads will have a water crossover that are bad about sticking try this first

[snmcharters]

The motor also starts to shake/vibrate a few seconds after the alarm starts going off. I was thinking one of the thermostats was bad because of this (thinking that only half the cylinders were shutting down). I guess the symptoms would be the same if the cross over was clogged as well. Is this true? Does this info help?

[cousinabe]

yes.
the engine goes into rpm reduction mode to protect itself when there is an overheat or oiling alarm condition.
are the heads too hot to touch?
what indicators are flashing on the yamaha gauge?

I replace my tstats every 2-3 seasons.