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?

I believe I remember somebody on this board mentioning they topped off their tank and fuel went into a vapor recovery tube or the like and didn't count towards the MPG the car calculated... not sure if everything was correct, but perhaps something similar happened to you.
Do you top off or do you stop pumping at the first *click*?
When you're done with this tank, manually calculate your mpg and compare it to what the car's computer says.

I just had my first oil change and recall done too- at 5500 miles.
my mileage is noticabley better also. I think it's a combination of the car breaking in, and the oil change. I had been hovering in the low 50's (51, 52, 53, 52) for the last few tanks (lots of short trip suburban driving) and suddenly my last tank was 56 on the guage, 55.2 calculated. The car also seems to be easier to coast/cruise above 60mpg at 80mpg. I don't think it's the gas.
yeehah. this is fun!
Kate

KLC
2005 HCH CVT 'Verdigeek'

This happens to me a lot. Even after 40K miles, I got 50.1 MPG last tank, 47.5 this tank. Same weather, same route. However over the long run, my mileage has gone up. It's not unusual to have "good tanks" - could be a combination of a lot of things. Enjoy it! Go another 4-5 tanks and see if it's a trend.

I have an Excel graph - can't figure out how to attach it right now. If I figure it out, I'll edit the post and add it.

Edit: Well, I can't figure it out. Here's some info on my 75 tanks for your entertainment.

Lifetime Avg: 45.47 (@ 40452 miles)
Best Tank: 50.09 (@ 39952 miles)
Worst Tank: 39.00 (@ 10626 miles)

Average variation in MPG between any two consecutive tanks: 1.84
Most variation in MPG from two consecutive tanks: 5.79 (@ 10626 miles - see worst tank)
Least variation in MPG from two consecutive tanks: 0.05

Statistically, 60-70% of my tanks will fall between 43.8 and 47.1 MPG
90-99% of the tanks will fall between 40.6 and 50.4 MPG

A lot of this variation is environmental (rain, sun/air conditioner, winter, wind, hills, traffic, etc.). I'm sure some is due to errors in the amount of gas that goes into the tank (I doubt the fuel pump "clicks off" at exactly the same fuel level each tank). Some honestly has no explanation - it's the magic and mystery of the hybrid.
Anyway, variation is expected. It's sort of sad that I know all the numbers.

Short answer is that your MPG should go up over time (car breaks in, improved driving habbits). Some will debate if the car breaks in at all, and the improvement is mostly due to learning how to get the most out of your hybrid. I think the car breaks in a bit, but driving habbits make the most difference.

Lastly, much has been discussed about gas. Most have concluded that octaine does not matter (go with what your car requires). I don't think a brand should make a difference - whatever minor difference it may make would be burried in the noise caused by the environment.

*** Retired after 65,000 outstanding miles ***

I dont know about other types of gas, and i dont drive many hills / stop and gop type of traffic but i have always used cheveron gas. In my experiance with cars i have always gotten the best mileage out fo the cheveron gas. i dont understand why, cause they area ll the same octane rating but i guess it has to doi with the additives they put in there. maybe it is formulated for hybrids, never know.

Ambient temp and a few degrees of humidity change can effect gas milage and performance greatly. you might not notice the temp or humidity change but your car sure will. Just my 2 C worth. Dean