Kick Auto

the marine thermostat is lower temp than automotive because the engine in the marine engine will plug the cooling passages if Higher temps are reached . in salt water the engine will evaporate and deposit salt inside of the engine destroying it.

There is a big difference not all of the automotive thermostats are made of the same high quality materials needed in this marine application

Some and you see I said some won’t hold up in salt water and will corrode.

Most auto stats have a vent hole so water can circulate even when the thermostat is closed. this sometimes prevents a marine engine from reaching proper operating temps especially in cold water

Temp range is Important because dissolved minerals in the water will start to form scale at very low temperatures around 162 degrees with the temp number given for a thernostat being the temp it starts to open and the fully open temprature can be as much as 15 to 20 degrees higher the correct temp thermostat to use is 140 degrees

If freshwater cooled then stainless steel automotive will work fine why stainless? has to do with the noble scale and dissimilar metal galvanic corrosion A brass one would only act as an anode and go away after time

Kilo covered most of why they are different but one other thing.The reason that a marine engine does not run as hot as an automotive is because in marine the engine is always reving at a high rpm and if they
ran it at a higher tempature the oil viscosity would break down much faster then normal.This would mean more oil changes and premature
engine wear.