2017 Yamaha 150 hp - 4 stroke warning alarm

[sullmate]

I bought this engine new. sits on a 2117 19 foot Hurricane deck boat. I have changed the impeller and housing twice. The engine only has 203 hours on it. Last impeller change was May 2022. I put the boat in the lake, fresh water use only, last week, and started it up. No problems. Pee hole was pissing normally. I gradually picked up speed. No problems until i hit 5000rpm.s Then the alarm sounded. I stopped shut engine off. No stream, the engine was not overheating, Restarted, no problem. picked up speed again, same result a steady alarm, no intermittent beeping. just a loud steady alarm at 5000 rpm. I also checked the oil. the oil level was perfect. No change in engine height. Same prop as last year, Is the overheat sensor a possible cause? Suggestions? Thanks, Sullmate

 

[99yam40]

what are your gauges telling you?

 

[sullmate]

no gauges, only the alarm. I am thinking that the thermostat is only partially opening, causing the alarm at high speed. I will replace with a new Yamaha t-stat and see if that fixes the alarm problem,

 

[99yam40]

you could pull the stat and test it in a pot of water as you heat it up to make sure it is in spec.
and while you are at it inspect the passages to see if there is a build up that needs to be cleaned up

Rydlyme marine descaler does a good job when needed

 

[sullmate]

Thanks, I will check t-stat this weekend.

 

[sullmate]

i swapped the t-stat for a new one. I ran the engine to 5K, It ran fine. no overheat. I tested the old T stat in hot water, It opened up and worked fine. This weekend i will run full throttle, Maybe there was a clog in the cooling system that is now disloged