2019 F25 Yamaha over heat light coming on.

[wvmedic]

Hello all, I have a 2019 F25 SWHC Yamaha 6FMK S. I have recently replaced the Impeller, not the kit, just the Impeller. After changing the Impeller the temp light come on at an idle in gear, seems to go into limp mode. I do a lot of trolling and haven't had an issue until now. The tell tale seems weak at idle and WOT, it has since new, that is in comparison to the old Evinrudes I've ran. I have ordered a thermostat and a water pump kit for it. The housing and plate looked good, no scoring on the original when I replaced the Impeller. The Impeller was an aftermarket not OEM Yamaha though. I have removed the thermostat and ran it without and still have the light come on at idle. I flushed the motor with the thermostat out and it flushed good, no corrosion that I can see anywhere. I might have 200 hours on the motor and has always been in fresh water. Does this motor have a poppet valve? Any ideas what the issue could be? I don't have a manual yet, I know I need one. I have no idea how to test the temp sensor with that being said.
Any suggestions will be appreciated.

Thank you, Jeff

 

[brodmann]

The temperature sensor can be tested by putting it in a pot of water and heating it up. You'll need an ohm meter and a thermometer. Start the stove and hold the one lead of the meter to the end of the wire and the other to the body of the sensor. At some point the temperature of the water will "set" the sensor off and resistance will go to "0". Note the temperature of the water at that point and then google your motor to see at what temperature the sensor 'closed". That's the point where the light comes on or the alarm goes off.

 

[wvmedic]

The temperature sensor can be tested by putting it in a pot of water and heating it up. You'll need an ohm meter and a thermometer. Start the stove and hold the one lead of the meter to the end of the wire and the other to the body of the sensor. At some point the temperature of the water will "set" the sensor off and resistance will go to "0". Note the temperature of the water at that point and then google your motor to see at what temperature the sensor 'closed". That's the point where the light comes on or the alarm goes off.

Thank you brodmann, I appreciate that. I'll check it if the new water pump kit doesn't solve the problem. I'm wondering if the cup is out of position. The cup has a small tab that sits in a slot in the housing for indexing. I'm just wondering if I had it slightly off.

Jeff

 

[boscoe99]

Sounds like a thermosensor is being confused with a thermoswitch.

 

[wvmedic]

Sounds like a thermosensor is being confused with a thermoswitch.

boscoe99, what do you mean?
Legitimate question, the only temp sensor I see Yamaha lists it as a thermosensor assembly.

Jeff

 

[99yam40]

switch is on(closed) or off(open)
a sensor has variable output(resistance/voltage)

 

[boscoe99]

boscoe99, what do you mean?
Legitimate question, the only temp sensor I see Yamaha lists it as a thermosensor assembly.

Jeff

Yamaha uses both thermoswitches and thermosensors (sometimes both) in different motor models.

A thermoswitch is normally open. (What Yamaha calls "off"). At some point it will close at a certain temperature. (What Yamaha calls "on"). When the switch closes the alarm will sound.

A thermosensor is neither open nor closed. It is simply a variable resistor who's resistance varies with temperature. Temperature goes up, resistance goes down. Temperature goes down, resistance goes up. When the resistance gets to X ohms the alarm will sound. The thermosensor also comes into play to tell the ECU how much fuel to add or not add. More fuel when cold, less fuel when hot.

A comment above by another poster mentioned the thermosensor closing. Which it does not.

 

[boscoe99]

Some Yams are sensitive with respect to water pump parts. One can take a gamble by using aftermarket parts and/or by changing just the impeller itself. If your problem started after you only installed the aftermarket impeller I would first try a Yamaha impeller and if the problem does not go away then install the complete water pump kit.

The cooling system is not where I would try and save a buck or too. Starter motors, yes. Regulator/rectifiers, yes. Propellers, yes. Impellers, nope.

Good luck.

 

[wvmedic]

Thank you 99yam40 and boscoe99. That's what I was thinking boscoe99, my local guy didn't have OEM is the only reason I bought a Sierra Impeller. I do have the OEM kit now, should be able to change it out this week and see if that fixes it. The one thing I found weird about the temp light and RPM reduction indicating an over heat situation is. There was no alarm, I was puttering along and decided to crank the throttle. That's when the motor stumbled and I noticed the light.

I've noticed that my variable trolling RPM switch isn't working either.

Jeff

 

[99yam40]

is this a tiller motor?
Not sure they have a buzzer.
remote have it in the contoller

 

[boscoe99]

Some Yams having a tiller handle have a warning buzzer in the tiller handle itself. I do not see a buzzer in your tiller handle. Seems that you get a warning light only. Plus RPM reduction mode which should give you an indication of the motor having a problem.

 

[wvmedic]

Yes, a tiller and no buzzer. The RPM reduction is what made me realize I had an issue.

Jeff

 

[wvmedic]

Changed Out the thermostat and did the water pump kit today. Took the boat to the river and had no issues at all, no temp light and it ran great

Thank you for the help.
Jeff