Temp alarm sounding @ 175 degrees

[Larry Baloun]

I have a 2008 4.3 ltr tks that runs around 170 degrees pretty consistently ...no problem. However, at times (at high rpm or under load) it will hit 175-180d Soon as this happens the high temp alarm beeps and will not stop until I stop the boat and rev in neutral to bring temp down.
I have checked manifold temp with heat sensing gun and it matches my gauge. Is there an adjustment on the alarm to make it sound at a higher temp. If not how do I fix?
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[alldodge]

Sounds like you need a new switch

That said, may also need a new impeller because motor shouldn't be getting that hot unless you boat in 90* or more water

What is the serial number?
AAnd open or closed cool?

 

[Larry Baloun]

Serial #1a312851. I put in an impeller and a new 160 degree thermostat. Water is about 70 degrees

 

[Larry Baloun]

Cooling is drawn from the lake.

 

[tpenfield]

Yes, I'd be testing the overheat sensor . . . should be both a 'sender' and a 'sensor (switch)' on the thermostat housing. . . and in the near term just disconnect it and keep a good eye on the gauge.

 

[alldodge]

Your SN list part 805218T (item 6) and specs show 190* open and 220* close +/- 10* (180 to 200 open and 210 to 230 close)

I would get another temp switch

https://www.mercruiserparts.com/bam/subassembly/31494/13798/170

 

[Larry Baloun]

Thanks. In the drawing you attach there is a sensor and sender but no "switch" .... which are you referring to? I have replaced the sensor, impeller and thermostat already.

 

[tpenfield]

Sensor = 'Switch'

The 'sender' is a variable resistor that changes it value with heat. The 'sensor' is a switch that goes off/on at a certain temperature (+/-), which activates that pesky alarm.