Good suggestions. I've heard is not good for a diesel engine to run cool. They like to run hotter. I think the previous owner had put a can of bar's stop leak every year for a long time for because he heard it was good for the water pump. There are no leaks. All that Bar's clogged the engine over time. I flushed it all out. Took 10 minutes of chocholate foam coming out before it ran clear. Also have a new 3 in. heat exchanger. Add the cold Puget water and maybe running 110 - 120 is ok. I'll use an IR gun and test the thermostat in hot water.
Bit of advise to all - engine was overheating and we looked at everything, themo, sea pump, water pump, heat exchanger, hoses, nothing we did worked. Then noticed gunk build up on inside of thermo housing, sea water pump and water pump. After flushing, overheating problem was solved. Be careful about additives.