It will run cooler, be inefficient and wear more quickly.
Stuck open thermostat.
A thermostat can be stuck open or closed. If the engine runs to cool it is stuck open. If the engine is running hot it is stuck closed. If you don't have these problems you should'nt have to change it.
Overheating if stuck closed, no engine heat if stuck open.
The thermostat is stuck open or missing.
The thermostat is probably stuck open, even when the engine is cold.
Thermostat is stuck open. Replace it.
If the engine is overheating, the thermostat is stuck closed. If the heater is not putting out enough hot air the thermostat is stuck open. Change the thermostat as a normal part of maintenance when changing coolant.
If the thermostat is stuck open, the engine will never warm up to proper temperature.
If the thermostat is stuck open, the engine will be slow to warm and may not reach normal operating temperature. As a result, performance of the heater will be poor. Fuel economy will probably deteriorate. And the vehicle may fail emissions testing (if this is required where you live). Furthermore, engine wear may be accelerated in the long term. For all of these reasons, if a thermostat is stuck open, it should be replaced as soon as possible.
No, generally an open or missing thermostat will make the engine run too cool.
It could be that the thermostat is stuck open.
Check the engine thermostat. Its probably stuck open.