Yamaha 150 ox66 2003 overheats/alarm/limp-mode and has no t-stats

[CCarl]

After about 5 minutes at 3500 RPMs the alarm sounds and the engine goes into limp mode. I figure it's the overheat alarm as I can see a bit of what looks like steam coming from the engine- slight as it is. Plenty of oil in both tanks, also. The pee stream is strong and steady. I planned to test the t stats but there aren't any.

What could be the cause if there are no thermostats. Thank you.

 

[99yam40]

stats are there to make sure all of motor is to the correct temperature for running and burning the fuel properly.
without them in place to control the water circulation properly, you will end up with hot spots and cold spots as some areas will not get enough water flow and others too much.

But the lack of stats in place is not likely what is bring in the alarm ,but I could be wrong.
IMHO Someone had this overheat problem pulled the stats and sold his problem.

running lean fuel/air ratio, plugged up water passages,scale build up not letting metal transfer heat to water, or water pump not pumping enough water to keep the motor cool
would be my guesses

 

[CCarl]

Thanks, 99yam40. Oh yes, I know the "problem was sold" by by the previous owner, but unwittingly- they are my good neighbors. They were taken for a ride by a f'n crook mechanic, and the band aid fix hasn't been realized until now. I don't think the absence of stats is what's causing the overheat or alarm, I just want to know what the next thing is to look for what causes overheating. You mention a couple of things, thanks.