Over heating alarm 90hp 2 Stroke Yamaha

[jamfordz]

I have just replaced the impeller and themostat on my engine it ran well for an hour or so then the alarm went off and the engine lost revs...I went back to neutral and shut engine down, it ran well for a time then the same thing happened again. What can I do ?

[jb123]

i think you have 2 thermostats, check or replace the other and check the prv valve under the lower right side starboard cylinder, could be clogged up.

[Hamfisted]

You have one thermostat and also a thermo sensor just below it. Might need to test the thermo sensor and see how its reading. When you get the overheat alarm do you get any steam out of the mid-section exhaust relief? Or with the hood off does the motor actually feel hotter than normal? I have the service manual for your motor in .pdf format if you need it.


Mike

[Ken]

jamfordz,
I would remove the thermo switch (sensor) and test it in a pan of heated water. You will need a thermometer and ohm meter.
The thermo switch is designed to close at around 180 degrees f., and then re-open at arond 160.
I have personally seen one go bad and close at 130 degrees, giving a false overheat condition and putting my motor into rpm reduction mode.
If the thermo switch checks out ok, then I would remove and test the new thermostat. It should begin to open at approx 120 f. and be fully open at 140 f. - min 3 mm or 0.12 inches.
The above procedures are explained in the Yamaha service manual - best to get yourself one - it will pay for itself.
Good luck [img]smile.gif[/img] ,
Ken K

[warren]

do you have a stream of water coming out of your water "pisser"? Mine was plugged with a piece of the old impeller and caused exactly the same problem with alarm and reduced speed due to restricted water flow.you'll have to take off the water jacket or blow the cooling system out to clear the passage.