I think you were refering to someone replacing a thermostat that had a higher cutoff point.
The 5-speed Insight is going into it's fifth year as the milage champ in the US. Whatever your milage is, it's better than driving something else.
I could make a long list of things to upgrade the milage of the 1974 Civic I had. It says a lot about Honda that they basically did everything possible to get great milage on the Insight so the driver would be limited to good maintanence and driving techniques.
If you read many posts, you get reported mpg ranging from 50 to 100. My 25-mile commute to work is about 85% freeway. Early some summer mornings in light traffic, I have gotten over 80 mpg cruising 50-55 mph. That's at least 15 mph under typical Dallas freeway traffic and near impossible to do during rush hour. I have also done about 50 mpg averaging 80 mph, keeping up with charging "men" with 5-litter engines. :twisted: Then three years ago when the roads were iced up, I did that commute off the freeway with extreme stop-and-go at 2-3 mph, getting 25 mpg.
You have to assume that there is a wide variation of both driving habits and traffic conditions. If someone talks about getting 85+ mpg on a tankful, I wonder if they were doing 50 mph on a quiet highway. The same person might be doing well to get 55 mpg in an urban area off the freeways during rush hour.