Well, I bit the bullet and installed the 180 thermo. I am hoping this doesn't lead to any difficulties in the long run. My reasoning was the canned fan settings in the tune are set for the lower temps so it was either reset the settings or change the thermo. I figure the lower temp might not be too much of an issue but I don't have a warm fuzzy changing what the engineers originally intended. Does anyone have a definite answer on why the 6.1 needs the higher temp thermo? Emissions? Clearances? Talk to me....