There ya go- a dominant (but not 100%) reason. The engine is always on for the 1st few miles anyway, but uphill, you're really suffering a lack of FE. And down around 45degF is where temp inefficiencies become really noticeable.

As regards the fuel consumption figures I at least can understand Aussie. Obviously Australia uses the same gallon that the UK does.

I'm an advanced driver who already has the anticipation and smooth driving sorted. I stick to speed limits (or lower if commuting) but I do prefer to get off the mark quickly (often redlining in 2nd on my way to 60mph). I am currently /almost/ getting 45mpg (9.46miles per litre) from my '02 1.6l Civic with a/c on full time.

I'll be very interested to see how much better the HCHII is for me. I'm not going to stop using the A/C so I doubt I'll be a chart topper. On the hour test drive I got the car up from 42mpg to 48mpg.

This is really driving me crazy.


My fuel consumption figures are all over the place like a dogs breakfast!

I can only think that it has something to do with the way I'm filling up. But once the filler "clicks" off for the first time, I can't get much more than a litre more in. So I can't be that far off!

For example. Fuel was cheap today so I decided to top up.

12.63 Litres (3.33 U.S. Gallons) and I had travelled 310k (194 miles)

This equals = 4.074 L/100Klm's 'or' 58mpg....correct?

Yet -

1/ I am usually getting around 5.4 L/100Klm (calculated)

2/ My posts show around 44mpg at the bottom (well maybe a bit different this time due to this last fill).

I fill up the same way every time!


Me no understand

It may seem like you are filling the same way every time but no matter how hard you try tanks vary. It looks like you last tank before this one was low so poerhaps this one is just balancing out for getting screwed last tank?

Or maybe you will pay next tank, or maybe you are driving better?

Start keeping track of what your display says and enter that in the notes for each tank.

This may be obvious, but...
Keep in mind that the less gas you need for a fill-up, the BIGGER impact even a 1/10 gallon difference will make in your MPG calculation.

Example - 100.0 miles driven on a tank, then fill-up:
First time it takes 2.000 gallons = 50 MPG.
Next time it takes 2.100 gallons = 47.62 MPG.
Did my MPG really go down, or was it a slight difference in when the pump clicked off (or otherwise in how I filled 'er up)? One may never know, but let's presume it WAS differences at the pump that introduced this 2.38 MPG difference.

Filling a "closer to empty" tank is always a little more accurate way to compute a tank's average, than is "topping up" and calculating that average.

Example - 500.0 miles driven on a tank, then fill-up:
First time it takes 10.000 galllons = 50 MPG.
Next time it takes 10.100 gallons = 49.5 MPG.

Whatever the gas-pump variable was has now only influenced the MPG by 0.5 MPG.

IF the tanks were filled identically each time, it would make no difference (except for rounding the miles/km to the nearest tenth). But that's difficult to do.

Bottom line is larger numbers work better for averaging than do small ones. For MPG, this is due mainly to differences in "how full did you really get it THIS time vs. LAST time". Also the accuracy of the pump's display of gallons/litres dispensed, and the accuracy of the odometer come into play. The odometer's accuracy (or lack thereof) is pretty consistent.
You can decide to always fill up using the same pump to reduce this variation.
Even the odometer may report distance inconsistently over time due to the wear of the tires.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL

Yeah...I think that's it.


Over the last several "fill ups" I've been topping up.

Therefore, as you say, a small variation looks much bigger.

I think I'll let this one go all the way.

Our fuel pricing changes daily. The cheapest day in Melbourne is Tuesday, ($1.31 per litre). The most expensive is Friday($1.42 per litre)!...and just before a public holiday add another 10c per litre

And the government watchdog says this is fair competition. Yeah right. Funny how ALL the gas stations do it at the same time!


I have actually noticed that when I think I can'y fit anymore in, the gauge shows one block off full? But only sometimes?

...and there's another variable. The gas station I've been using for the last few fills has a slight downhill slope towards the filler side!

Hmmmm?

I've always filled up to the filler neck. It's 100% accurate, and based upon my inspection of the parts catalog's illustration of the tank, there is absolutely no way I can do any damage to the vapor recovery system this way. There is a huge air space in the top of the tank. Pumping the 2.0 gallons after it clicks off still leaves a big air space for the vapor system to work. I can post the illustration, if anyone wishes to see it!

Nothing is 100% accurate. Unless you fill at the exact same pump parked in exactly the same position so that the car is always exactly the same degree of level more or less gas will go in the tank. Even if you did all that the gas pump could be off and so could your trip meter. In fact since tires wear smaller as they age your trip meter is bound to be off at some point in the tire's lifetime. How hot it is can also throw a monkey wrench in the works. PV=nRT and all that rot.

Okay then... 98% accurate! Or... at least... more accurate than just going to the first click-off. I can see the level floating in the filler neck at approximately the same level each time, on assumed-to-be level ground.

The pump could be inaccurate, but the state measurement certification inspection is supposed to take care of that!
Tire wear should not be a statistically significant issue from one tank to the next (600 miles), though I agree it will make a difference within the life of the tire.

Tire pressure and temperature could also make a minor difference to tire circumference (but I always maintain 40 psi, so it is consistent).

Temperature could make a difference in the volume of fuel, as well as in the vapor pocket within the tank.

I believe all of these issues combined would make a statistically insignificant change (less than one tenth of a mile per gallon).

Speaking of tenths of an MPG... Anyone wish the "A" and "B" MPG meters had hundreths? How about an arrow on the instant gauge to indicate that your present MPG is above or below your average... that would be slick (it's on my bike computer for average speed!). More for the wish list on future HCH's!!!

I might give you 98% in the short term but if I remember correctly your tires wear about 3% over their lifetime so in the long term you would be looking at worse than 98%. Of course the tires would also throw off the display so one is not really better than the other. Perhaps the best would be a navi system with GPS (so long as you always had GPS coverage). Or we could just not worry about it.....

I wish we had "A","B" and lifetime at least in real tenths, hunderedths would be even better. The gen one display jumps 3 or 4 tenths at a time and the instant bar graph jumps like 4 whole mpg at a time, does the fancy new gen 2 do real tenths?

I like the pointer idea.

Man we are getting off topic, I'll send myself a warning in a PM.......