"Any motor that is capable of
"Any motor that is capable of being fitted with a thermostat will always run better if it has one.
I will defer to a write up provided by Joe Reeves, a retired OMC master tech who has contributed greatly to this site.
Here is his explaination -
Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperture to compensate for the distortion.
With the thermostat removed, the difference in temperture between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder, or vice versa. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.
The thermostat in your car isn't there simply to have the heater function properly..... think about it."
