Accuracy of miles left on tank

[guest1875]

I know that even the clever guys at Honda can't predict the future, but I'm a little surprised at how badly wrong the estimate is for the miles you can get from the fuel left in your tank. 

And I appreciate the estimate will vary up or down as driving conditions vary.  But I've done just over 1000 miles now, and do a pretty consistent journey every day with a pretty consistent fuel consumption, pretty consistent around the 48 mpg mark.

So, when I fill up the tank, the car should know exactly how much fuel there is, and should have a pretty good idea that I'll be driving around the 48 mpg mark, so it should know pretty accurately how many miles I should expect to get. 

However, just after filling up yesterday it was telling me I could expect 470 miles out of my tank.  But in fact I only seem to be getting around 300 miles, each time averaging around 48 mpg.

So why is it so wrong?  The mileage estimate seems to drop like a stone towards the end, to catch up with reality.  If anything, I'd expect it to err on the side of caution, telling me I had fewer miles left than is actually likely.

Thanks.

[eljuero]

I guess that 470 miles is expected milleage with full tank (using all gas) regarding your last mpg.
But becasue of the shape of the tank sensors are somehow unable to give the correct information about expected milleage later, what is most obvious at the end. I can't really understand why. But the fact is that when the car computer tells you "0 km left" there is still more than 9 liters left in the tank.
If you got the same mpg as before fill-up, then you should be able to drive additional 170 miles with the rest of gas ... approx.
As I said before in previous threads this feature is therefor useless in Jazz.
I wonder if this error is resolved in the upcoming facelifted Jazz

[guest1875]

Hi

That does start to shed a bit of light on it.  I see that the fuel tank has a capacity of 42 litres.  So with my 48 mpg (= 10.6 miles per litre) I should be getting around 445 miles.  And that isn't too far off what the computer initially says (maybe in the few miles leading up to refueling, I was doing > 48 mpg so that the computer's initial estimate is > 445 miles).

What has confused me is that the computer seems to start panicking about low fuel a little prematurely (and I understand why it should).  So I've been refueling at around the 300 mile mark, when the fuel light comes on and the estimate really starts dropping rapidly towards zero.  In fact there is probably another 12 litres or so in the tank at this point, which would give me another 130 miles.

So perhaps the initial estimate from the computer is what you might expect on all 42 litres in the tank, but it gradually shifts to basing it on you having only a ~32 litre tank, as a precaution, so that when you hit zero you still have extra to get you to the next fuel station!

[eljuero]

So perhaps the initial estimate from the computer is what you might expect on all 42 litres in the tank, but it gradually shifts to basing it on you having only a ~32 litre tank, as a precaution, so that when you hit zero you still have extra to get you to the next fuel station!

Well, I'm sure this is an official explanation given by Honda  (at least I was told so, after several months of "thinking" what is wrong).
If you ask me, if the car computer was too pessimistic for 50 km, it would be enough.
Warning light does pop out very fast (when approx. 10 liters left) , so if you are afraid you might end up w/o of gas, you can go refilling it as soon as possible,  but if you live in the area and country where gas station is on every corner then the right information of expected mileage (if the car has this function) would be welcomed.
As I stated before I help my self with "mpg" data I'm getting from my board computer. I have to add 0.3 l/100 km though, because it's too optimistic. If my real avg is 6 l/100 km, I know that I should be able to get mileage like 700 km (42:6=7) if I keep this mpg, otherwise just recalculate. But I must admit that the psychological effect is a b****.
Knowing that I don't understand why Honda didn't tie expected mileage info to the mpg.
Therefor perhaps, just perhaps  your theory can be  right 

[guest806]

Wouldn't it be good to have an on board computer linking this to the sat nav and tell you how many service stations are in the proximity of the amount of fuel left.
Perhaps i should go to Honda with the idea!

[guest1948]

Hi! This topic is the exact reason why I registered - glad to see it's not just me seeing curious behaviour from the computer.

I mainly do motorway mileage (450-500 a week) and have noticed the following whilst sitting there at 70 ish:

• With a full tank it claims a range of 450-460 miles
• On the road it claims 49-50 MPG - which ties in fairly well with the claimed full range
• After a while the driven+remaining total will fall to around 400 miles and stay there
• Once I get to around 160 miles remaining, the driven+remaining total plummets - the "160" miles is usually no more than 100 so I'm "empty" at about 340 miles
• On refilling I reckon I'm actually getting 45 MPG or thereabouts (which ties in with the 400 mile driven+remaining calculation now I look at it)

Does that fit with what others are seeing?

[guest1925]

• With a full tank it claims a range of 450-460 miles
• On the road it claims 49-50 MPG - which ties in fairly well with the claimed full range
• After a while the driven+remaining total will fall to around 400 miles and stay there
• Once I get to around 160 miles remaining, the driven+remaining total plummets - the "160" miles is usually no more than 100 so I'm "empty" at about 340 miles
• On refilling I reckon I'm actually getting 45 MPG or thereabouts (which ties in with the 400 mile driven+remaining calculation now I look at it)

Does that fit with what others are seeing?

Yep I see this with my car!  I work from what miles I have done and usually fill up at around 300 to 330 miles on the trip that way I feel I can't get caught short especially as I have no filling stations within 15 miles of where I live.  I watched the mileage left in the tank plummet from 25 miles to 0 on a 6 mile journey and had not changed my driving style!

[guest1272]

I was told it does this because the fuel tank is very shallow in order for them to move it further forward (under front seat) for the new shape Jazz.

The downside to this is that, whilst fairly accurate when full, the accuracy of the gauge reduces as the tank empties because what little petrol there is is "shallower".

Now, I read this from a US site and, truth be told, I have difficulty wrapping my head around the logic behind it, but it's the only attempt at an answer I've ever found.


On that note, my Jazz behaves the same but I track my fuel consumption using an app on my iPhone. The Jazz's trip computer is consistently overestimating average fuel cons by about 1.2mpg..........well, at least it's consistent  .

[Geoffers]

Yeah, we also operate on filling up at around 300 miles. SWMBO has a 70 mile round trip each day so she will fill up here (BP garage) when the mileage is more than 240!

We never use the 'remaining miles' feature.

[dogbiscuit]

I know that even the clever guys at Honda can't predict the future, but I'm a little surprised at how badly wrong the estimate is for the miles you can get from the fuel left in your tank. 

The estimated range as shown on the multifunction display is complete waste of time. Leaving work for home yesterday, a journey of 6 miles with an estimated range of 13 miles showing it hit 0 miles before I arrived home.

[guest1272]

However, just after filling up yesterday it was telling me I could expect 470 miles out of my tank.  But in fact I only seem to be getting around 300 miles, each time averaging around 48 mpg.

Isn't that a bit low?

I am averaging 39mpg around town (urban driving only - never taken it on the mway yet).
That's 8.5876 miles/litre
For a 42 litre tank, that equates to 361 miles per tank.

Road Trip (iPhone app) agrees, telling me I should get 362 miles per tank. However, because of the fuel light coming on "early" I, on average, end up filling up on the 275 mile mark (ie about quarter of a tank left).


If you're averaging 48mpg, you should be getting about 444 miles/tank

[guest1730]

All fuel guages have always only been an indication that there is or is not any petrol in a tank. Old ones used to use a float that could get stuck and was often affected by debris which accumulates in the tank. Not sure how the Jazz works but I would never assume that it is right. Also the tank is seldom totally full even if showing full on the gauge.

Best way to check mpg is to record start mileage when tank full, then drive normally for several weeks/months keeping a note of fuel added from known start position to known end position(full). The longer you do this for the more accurate the mean mpg will be.