I got my HCH in late April. About 5500 miles now on car, got my first oil change/recall computer stuff done 3 weeks ago. The best mileage I've reached was 46 once, with only about 1/4 tank gone- I almost always run 41-42.5 mpg on my weekly commute, east bay to & thru San Francisco, 32 miles each way (and lots 'o hills, traffic, a tunnel and a bridge).

Monday AM I get gas ($27/10 gallons- sigh!) right before we get on the freeway. Usually go to Costco on Saturday, but it was crazy busy, so I went to an expensive Chevron last minute (still using their cheapest grade).

As I reach San Francisco, I'm showing 49.9 mpg that first day. NEVER been that high. Slowly goes down to 48 by Tues. evening (with about 140 miles on the tank). Tues. nite the puppy runs away, spend 2 hrs going very slow, stop and go, around neighborhoods and it goes down to 45. . .

Wed., back up to 46. . .
Today, back to 46.5. 300 miles now on tank, only 1/2 gone. . .
Amazing!

Could it be the Costco vs. Chevron gas? Could it take 5500 miles to break in? Does it matter if you jump on the freeway right after you fill it up vs. drive around town for a day or two? Is 3 weeks after the first oil change special???
Heck, I don't want this to end. I didn't wash the car last week. . . maybe I should leave it dirty???
Can anyone help me figure this out?