The heater core may be plugged or not flowing properly. This would not allow the water to flow properly to cool the motor. Also you may have a bad or loose ground wire to your heater switch, this will give you a false reading on the temperature gauge.
The temperature of the coolant entering the heater core is controlled by the engine thermostat. The engine coolant thermostat is generally located at the engine end of the upper radiator hose.
In a hot water heater, a thermostat regulates the heat
Check into the temperature control valve--this is different than the thermostat.
Someone turned up the thermostat, or the thermostat has failed. The thermostat tells the heater what temp to keep the water at.
The wattage of electric base board heaters does not change because the thermostat is set on low. The wattage is a fixed value on the heater because of its internal resistance element. The thermostat set on low shuts off at a lower temperature than a thermostat that is set on high. It is the time interval that governs the amount of heat that the heater produces when the thermostat calls for heat. Once the room heats up to the temperature that the thermostat is set at, the heater shuts off. The thermostat is just a temperature switch.
Yes, you can set the temperature on this device.
My first guess would be a thermostat stuck open. Replace the thermostat.
Low on coolant, stuck open thermostat, plugged heater core, faulty temperature blend door,
The thermostat is not the issue. The thermostat regulates the engine temperature, but not the heater core temperature. There is a valve going to the heater core that is not closing all the way. It may be broken, clogged, or not actuating.
Try your thermostat
The engine's thermostat controls the engine coolant temperature. The temperature control inside for the heater controls the cabin heat.
Low coolant? Bad thermostat? Heater core plugged, restricted, or airbound? Temperature control cable not working?