yamaha 115 alarming and cutting power

[sporadic]

I have a 1999 Yamaha 115, 2 stroke. It recently started alarming when I was cursing around 4500 rpm the harder I push the engine the quicker it alarms, if I sit at 3500rpm it will keep going no problems. When the motor alarms it cuts the power to an idle. There is a decent flow out of the telltale and it does not seem to be hotter that normal. I’m thinking it’s a over heating problem. Is this a common fault with these motors at this age and any suggestions as to what to try first?

[boatmangc]

Start with an impeller, then service your pressure relief valve

[axolotl98]

Replace both thermostats as well.
I would suggest to do that before messing with the pressure relief valve

[99yam40]

Would not hurt to make sure the alarm is the over heat and not oil level.
Do you have instrument package that will give indicators of low oil level and over temperature?
You could have a restricted oil filter leaving the remote tank.

If it is not oil then check heads with heat gun when alarm goes off.

Testing the temp switches and t-stats will be easy to make sure they are functioning according to the book.
Sticking PRV usually causes low RPM over heat not high RPM.
If everything is working properly then water pump and cooling passages will have to be looked at

[boatmangc]

Thermostats normally will cause overheats at low speeds, the pressure relief valve opens up at higher RPMs to allow more cooling than the open thermostats can provide.
But again; Start with an impeller...

[rodbolt17]

gotta dissagree on BOTH.
the Tsats can and do stick and give partial openings causing overheat at high speed.
the Pressure control valve CANNOT cause high speed overheat on V yamaha engines.
any excess water pressure issimply dumped back into the exhaust tuner area and overboard.
the PRV can and does occasionally create low speed issues due to dumping the water pressure(water) at low speeds if its stuck open or missing.
at high speeds water pump volume cn overcome even a missing PRV valve.
seen to many removed in an attempt to solve a problem by folks with no clue how or why the system works.
typicall on high speed overheats,after normal maint is done, that includes water pump repair kit,t-stats and pressure valve grommet replacement?
typically its either scale on the block or a head gasket that is leaking combustion gasses into the cooling system.

[Michael j]

A water pressure valve that is stuck closed or tight in grommet will not let the water thru the block fast enough to pull the heat out. That with a old impeller will let it overheat sooner. I'd do the water pump, water pressure valve/ grommet & T stats.
If you get a alarm after a hard run and the oil tank on the motor is low and it is slow to refill replace the oil filter on the back of the oil tank. It's a good idea to replace it when you do your service.

[rodbolt17]

wrong
on the V yamaha a valve that is stuck shut will simply increase block water pressure.
a valve stuck partially open,more common, will simply dump water into the ex cavity and overboard thus dumping block pressure at idle speeds causing the top stbd cyl to lose cooling water and the complaint is a hot horn in about 5 min below about 1100 RPM.

water flow on the V4 2.6L v6.
water enters under both v banks and enters the ex cover area.
that is where both the tell tale AND the pressure control valve is located.
tell tale water is taken BEFORE any cooling has occured.
excess water from the water pressure control valve is simply diverted through a tube and into the ex tuner cavity and down and out the prop cavity, again, before ANY cooling.
pressure control valve is long before any block or cyl head cooling areas and simply controls water pressure in the block.
thats why taking the t-stats out isnt good.
with the t-stats out the PRV CONNOT work as instead of two restrictions (t-stats) you would have 2 open holes and it dumps block pressure,now the PRV is another part along for the ride.