2007 Yamaha F250 overheat at Idle

[keys diver]

Hi, my F250 is setting off the the overheat buzzer when in gear and at idle. It has also just recently started to overheat at idle when out of gear as well. So far I've replaced the impellers and thermostats.
When I hook up the ySD cable and monitor the engine, next to the two temperature fields that say <120 I'm reading 70 and next to the <248, I'm reading between 160-170. Should the buzzer go off at these low temps?
Also, when referencing current faults with YSD , nothing shows up to indicate an overheat has taken place. At all other rpm ranges the buzzer never goes off.
After the buzzer goes off, I can shut the engine down and immediately restart the engine and no buzzer

Any Ideas?
thanks

[99yam40]

have you thought about replacing the PRV?
if stuck open it will dump too much water so the power head never fill up with cooling water at low RPM
higher RPMs push more water up

[pstephens46]

May need to look at exhaust for corrosion issues too.

[fairdeal]

When I hook up the ySD cable and monitor the engine, next to the two temperature fields that say <120 I'm reading 70 and next to the <248, I'm reading between 160-170. Should the buzzer go off at these low temps?

Those temp numbers are expressing the same single point of measurement, just that one is in Celcius, the other Fahrenheit.
The overheat buzzer will not be triggered by that temp value until it reaches >248F (which is 120 C)

However the overheat buzzer can also be triggered by either of the thermoswitches which sit in the thermostat housings;
even if the "temperature" value is below 248
you can see the switch status in YDIS:



Its normal for "simple" overheat to not store a code,
its normal for the overheat alarm status to reset when the engine is turned off and restarted.

of course its not normal to get overheat alarms at idle -
but that IS a symptom that water flow is being lost between the pump and the block.

You could remove the PRV as 99 suggests (although I doubt it is the problem)
You could remove the thermoswitches and test them for proper functioning

personally, on a "2007" F250 -
I would start by dropping the LU, connecting a garden hose to the water tube,
and see whether or not I have water coming out the muffler....

[rodbolt17]

me? I would drop the lower and check the ex stack with my bore scope.
to store a code the thermosensor must agree with the thermoswitch.