The thing you are all ignoring is a car may start up at 0f or colder and they
will run a 210f thermostst, with the oil running hotter than that. In a boat
the thermostat is almost 100 degrees cooler (typically 120f on a 4s outboard
and I doubt most folks will start it at much under 65 or 70f.)
That operating range for the oil is a small fraction of what it is in a car.