Bob,
I agree with your instructors that the temperature should run around 190° as a general rule. It would seem that the mix of sulfur and water cause the sulfuric acid that can, and will eventually strip the engines internal lubricants and eventually cause excessive wear and damage. The higher heat range tends to burn off the H2O and keep that process in check.
IMHO Yanmar, and many other Japanese tractor engineers, have overcome that problem by simply stepping up the routine maintenance of fuel, oil, fluids and filters ranging from 50 - 100 hours, OR when visible debris is evident in the tank and fuel bowl. This, and a proven Cetane booster all but eliminates the H2O/Sulfur=Sulfuric Acid problem. It is my understanding that 50% of service calls are fuel contamination related in the Tractor, marine and stationary diesel engine service calls. It only takes 0.5% saturation of water and sulfur to produce sulfuric acid at the point of ignition....but it may take several weeks or months to produce the correct circumstances that a filter change and Cetane booster eliminate.
That's why many "Old Timers" keep their tank topped off to avoid condensation, routinely drain the water separators and change fuel filters when they look just a little cloudy. I have a 1610D and 1601D, the '10 has 620 hours and the '01 has nearly 1800 hours. Both tractors have identical engines yet the 1601D runs and operates flawlessly with close to three times the hours. The 1610D has been plagued with problems....I am convinced that the difference between both tractors is one has been rigidly maintained and the other badly service neglected.
Mark
