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Discussion Starter · #1 ·
On my non-microskiff I have a 150hp Yamaha 2-stroke and the alarm sounds from time to time. with this, my yamaha will shut down to a max 2000rpm. usually after about 10minutes of shutting the motor off, the alarm wont sound the rest of the day or sometimes it will. there is plenty of oil & pee stream is solid. i did notice the water in the stream is hotter than usual when the alarm is sounding. is this another thermostat problem? its driving me freaking crazy. thanks
 

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How old is the motor?
When was the last time you replaced the impeller?
It is possible you have a sticking thermostat or a partial blockage in the water jacket.
 

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Discussion Starter · #3 ·
the motor is a 2003. the impeller hasnt been replaced for about 2 years. i have tried to snake heavy leader through the outlet and inlets and no gunk or blockage that I can see. the alarm has been a problem for some time. i had it looked at a year ago and my mechanic said the old owner tried to give it a tune up- wrong spark plugs, wrong idle adjustment, and the list goes on and on. he fixed everything he saw wrong ($$$$). now the alarm is coming on again...and again. impeller and thermostat is not that bad of a job for a rookie, right?
 

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Get the OEM shop manual and follow the instructions.
Take your time, do it right. It's not hard, just time consuming.
 

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look for a poppet valve. Had a bad one on an older Johnson Ocean Pro 115. Replace it and the overheat alarm problem went away.
 

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Never had a poppet (pressure relief valve) stick or clog before,
but if one did it's easy to access. On a V6 block it's usually located
on the bottom half of the exhaust cover. Has a hose attached to it
and several screws that seal it. Remove the hose, loosen the
screws, remove the neck and plate and the valve pulls out.

http://www.yamaha-motor.com/outboard/parts/home.aspx

hunt your year and model, select crankcase to view the components
 

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Discussion Starter · #7 ·
thanks guys, I cant tell you how much time, and also money, I spent on this already. its crazy cause the motor runs soooo good if the alarm isnt ringing in my ear.
 

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Discussion Starter · #8 ·
just an update for anyone out there...took off the old thermostats, dropped them in 160degree water on the stove top. one opened like designed, one didnt. replaced both thermostats, ran the boat about 40 miles a week ago and problem fixed. thanks guys
chris
 
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