57 mpg! can't believe it!

Nice job. I've had work commutes (37 miles) where I've averaged 62-63 mpg but my best tank ever (over two years) was 54. Can't complain about that though. My Xterra only got 15 mpg.

Also, I've never had a tank cost more than $35 in the past two years either.

 

Nice! Mine has gone up as well with the nicer weather, although I can't stop myself from using Power Mode and driving like a normal car (no gas saving technique)... but I still manage 52mpg on my daily commute!

 

Is that in Imperial gallons or US gallons ( around a 20% difference)

 

Congrats! Have hit 57mpg's or better 7 times so far in 37 fill ups. The Prius makes it easy to drive a lot more. Day trips to the shore or mountains are no problem now.

 

My best so far has been 58.9 MPG on a tank I rechecked 3 times before I could believe it

 

Definitely temperature and tires will impact your fuel efficiency. Weather as well. Wind, rain, cold, standing water, snow, ice, non low rolling resistance tires, decreased tire pressures, cooler battery temperatures all conspire to lower your overall fuel efficiency. However, when the weather warms and dries up, the MPG's return (like migratory birds).

What you are seeing is normal. There are things you can do to limit the decline, but not eliminate it. Still, 48 mpg as your lowest tank isn't too shabby, now is it?

 

You are a prime candidate for grill blocking your lower grill. It will speed up engine warmup times and reduce cool down (especially when you are running the heater).

 

Altogether not more than 10-15 minutes by yourself for the first time.
Next year with the foam insulation pipes already cut from previous season - 4 minutes

 

Get some pipe insulation, cut to appropriate lengths, cut some vertical slits in the "seam" side so the insulation can slide between the vertical support bars on the lower grill, push into place. I found that I could get 3 pieces (1/2"?) wedged in there with no need for twist ties. The upper portion of one insulation wedged into the lower portion of the piece above it. Kept the whole thing in place. Worked a treat! I need to get it back in place this weekend, as our low temps are coming back, and I like getting the heater on sooner rather than later. And without twist ties, it is easy to remove when washing the car or if the weather warms up.