Lower Range
There's a bit of a dilemma here in that, although Diesels like to run fairly hot, the 5411 is raw water cooled and there's a threshold at which the salt and other minerals will precipitate out and clog up your water passages. I believe that it's around 176 degrees or so, which leads to about 150 being optimal. Although the engine would be very happy with the 150-180 range, it would result in precipitation and ultimately in clogged water passages. If you watch your gauge, you'll notice that the temperature will fluctuate +/- 15-20 degrees or so as the thermostat lets in more or less cool water. This is especially noticeable before your engine block's mass heats up and stabilizes. Additionally, the 5411 cooling system (I assume the 27 is the same as the 30) is a bypass system that re-circulates the heated water and only lets in the cool water as it needs it. Therefore, when the engine is cool, very little water will come out of the exhaust. Even when it has reached operating temperature and is in a steady state, it doesn't exhaust as much water as other boats. Don't worry, it's normal, but you'll get a lot of helpful warnings from other sailors. You'll also get a bit of white "smoke" that's really steam.
