140F thermostats are typically used for raw water cooled motors in saltwater. The salt comes out of solution over 140, so a 140 thermostat minimized buildup due to salt. In freshwater raw water cooled motors they typically go to 160. In a closed-cooled system you have a lot more flexibility and they typically run even higher temperatures because the engines are more efficient. You should be fine running ANY temp thermostat and not having an overheat unless the thermostat is faulty or there are other issues in the cooling system - it won't be because the thermostat is the 'wrong temp'.I do not know much about thermostats. The guy at the boat store said I need a 140 thermostat for my motor, so I went with that. Both motors typically run at 160, not sure if that makes sense for a 140 stat? My temp gauge gradually climbs to 160, and never moves or fluctuates beyond that. I did not consider that the brand new thermostat could be bad.