Originally Posted by willwren
I have a mildly drilled 180 INTENSE wide-mouth thermostat (two 1/16" holes) in my 95 SLE(supercharged). I get 31mpg on the freeway at 70mph.
I have a heavily drilled 160 INTENSE wide-mouth thermostat in my 93 SSEi and I get 32mpg at 75mph.
I've never seen a decrease or increase in fuel efficiency based on a thermostat change in either car.
Other factors play a big part into this, such as type of driving, elevation and changes in elevation, overall system changes, and accessory use.
Using the AC will have an affect on the MPG, the other modifications, and the lay of the land (flat driving VS hilly, Stop and Go VS highway)
I know with my 93 SSEi, 25-26mpg is an EXCELLENT trip, while my 93 SSE was good for 28mpg on the highway. Mind you, neither of these cars was modded. And I did see better mileage when I was in Rochester (flatter) than in Binghamton (hilly).
The change from the long commute to the short one probably had an effect on your MPG, and the 180 may have as well since your commute is shorter, it could be coming on sooner in the trip. How much of a change it make, I am not sure we have done any valid test/research on yet (that I have read). You may want to replace it with the 195 and see if things improve and report back.