Thermostat

[UpperPintle]

Did you resolve your engine thermostat question?

I also have a M5444 and the manual specs running temp of 175 - 180 degrees.
The Napa thermostat (part number) THM 115 keeps my engine temp at 180.

Attached is a Universal service manual

 

[T33]

Yes. Tested the thermostat in heated water and it works fine. it turned out the engine was in need of a flush, clogged with gunk that prevented free flow.

 

[jibes138]

Thermostats have a weep hole that allows a small flow of coolant even when closed. Have you done the IR test on the thermostat housing? If working fine in the heated water test it really sounds like a gauge calibration issue. Another option to try, pull out the thermostat and run the motor without it. See what temp it runs at. The coolant tank is another place to check. Run the motor with the cap off and put a thermometer in the coolant to see what the temp of the tank is.