My 2002 S60 usually shows an average mileage of about 16.5. Most of my driving is back and forth to work, in Pittsburgh where everything is a hill. I usually reset the average after a long highway trip and the number settles back to 16.5

When my thermostat failed and the engine was running cold, average mpg dropped to 16. That's average without resetting it when the t-stat failed, so I'm sure my failed t-stat mileage was much lower.

I replaced the thermostat with a 92 C version instead of the 90 C standard one. My hope was to get more hot air to keep my toes warm but I figured that fuel economy would go up a bit.. I did reset the average mpg and after a couple weeks of back and forth to work it reads 17.3 mpg. A 5% increase. Not enough savings to send me on vacation but with the price of gas every tenth help. I'm now curious to see what mileage will be on my next highway trip, I usually get 29 mph.

 

Gas blend has changed from winter to summer. Summer blend is about 10% more efficient.

 

According to EIA.gov, the change doesn't happen until May.

 

May 1st is when the supplier tanks need to be fully purged. Most distributors are already supplying it. Switchover begins in March, takes a couple months to complete.

 

Not quite ten percent.

 

Since I'm still using gas that I bought in February with my fuel points from the grocery store, that point is moot.