shou3n

Petrol mileage display

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Hi all,

Usually when I fill my fiesta up, the mileage displays around 450mls at full tank. 

Past couple of times, it only displays around 250-280mls. 

Any idea why this please?

Thanks. 

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Have you changed the way you drive  - lots of short journeys ?

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Yeah, I don't drive as far, or as much, for work anymore...

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57 minutes ago, Tiexen said:

Have you changed the way you drive  - lots of short journeys ?

Yeah I don't drive as far, or as much, for work anymore..

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That'll be why then. Your MPG has dropped due to the short journeys and city driving rather than a constant speed on the motorway. The mileage remaining is calculated from the MPG you get and the amount of fuel left in the tank.

For example:
If you were getting 50MPG and had 2 gallons in the tank, you would have 100 miles to 0
If you are now getting 30MPG and still have 2 gallons in the tank you would have 60 miles to 0.

So Miles to 0 = MPG * Gallons in the tank.

I've done the calculations for you, and as the fiesta has a 42L tank (9.24 gallons), I've calculated your MPG figures off the mileage you were getting above.

You were therefore getting 48.7MPG (450 miles per tank) before
You're now getting 28.7MPG (265 Miles per tank).

That seems a very low MPG figure, try resetting the MPG figure by holding in the trip computer button for a few seconds and see what you get after that.

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So does this mean when showing 0 miles there is still actually a gallon or so left in the tank so there is still 30-50 miles till it actually runs out?

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yep , but i wouldnt keep going for another 50 miles . lol

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The computer assumes an average based on your MPG,
Usually mine will say 250 Miles on a fill up if all I've done that month is short work & shopping trips,

When I've made a long trip to Cornwall and fill up down there it will say 380 Miles on a full tank,

That's due to the long cruise down getting 46mpg, compared to my shocking sub 25mpg heavy footed short urban trips.

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4 hours ago, iantt said:

when showing 0 miles theres 5 litres left .......

ha ha !

i suspected that !

i've been playing chicken with my miles till empty gauge and got as low as 2 miles before filling up.

now i know it has more to give lol

 game on !  :-D

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ha ha !
i suspected that !
i've been playing chicken with my miles till empty gauge and got as low as 2 miles before filling up.
now i know it has more to give lol
 game on !  :-D

oh dear, wish i hadnt mentioned it now.

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10 hours ago, biff55 said:

ha ha !

i suspected that !

i've been playing chicken with my miles till empty gauge and got as low as 2 miles before filling up.

now i know it has more to give lol

 game on !  :-D

The Mk2 seems to think the tank is 'empty' way before it actually is, I got mine down to 0 once, and it just reset to 30 miles... :laugh:  Never even coughed and was still nowhere near empty with the amount of fuel I could get in.

The Mk6 Fiesta on the other hand, said it still had 20 miles left with the gauge on the stop...then I put more petrol in than the stated tank capacity. :unsure: 

 

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10 hours ago, biff55 said:

ha ha !

i suspected that !

i've been playing chicken with my miles till empty gauge and got as low as 2 miles before filling up.

now i know it has more to give lol

 game on !  :-D

Be careful with doing that:


As the fuel level gets low the car will start picking up debris from the bottom of the tank. This can damage both the fuel filter and pump. The catalytic converter can also be damaged.

Running out of petrol can cause the fuel pump to run dry, which could mean a £200 garage bill.

With diesel cars, the engine management system shuts down before you run out of fuel, this prevents damage to the vehicle - but with petrol cars there's no system like this in place.

Stranded motorists account for nearly 50,000 of the AA and RAC’s callouts every year.

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i understand that it calculates miles to empty based on my mpg but my mpg over how far back?

The mpg for the last mile, 10 miles, 100 miles, since last fill up, since I last reset the mpg gauge, the last day, the last week, since I last started the engine?     Does anyone know?

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Since you last reset the mpg gauge

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 My 1.6 petrol in the summer says 310 miles to empty when full. Filled it up couple days ago and said 260.

Its driven mostly 3.2 miles to work and back 5 times a week.

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On 1/29/2018 at 11:01 PM, Mordey said:

 My 1.6 petrol in the summer says 310 miles to empty when full. Filled it up couple days ago and said 260.

Its driven mostly 3.2 miles to work and back 5 times a week.

My 1.6 titanium 2011 is around 270 to 300 from a full tank,only let mine go just under half and then fill it up,very short trips,car don't even get warm.

Normal for a 1.6 non eco.

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3 hours ago, jace1969 said:

My 1.6 titanium 2011 is around 270 to 300mpg from a full tank,only let mine go just under half and then fill it up,very short trips,car don't even get warm.

Normal for a 1.6 non eco.

270 to 300 mpg! Damn son, I need one of those!! :cool:

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10 hours ago, Mordey said:

Since you last reset the mpg gauge

I thought this but there must be another input for it, I always reset all trip readings when I get to the fuel pump so everything is on 0.  After filling up and restarting, the range is always different, so it's not like it just defaults to say 600 miles when the avg MPG is on 0.

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2 hours ago, TomsFocus said:

I thought this but there must be another input for it, I always reset all trip readings when I get to the fuel pump so everything is on 0.  After filling up and restarting, the range is always different, so it's not like it just defaults to say 600 miles when the avg MPG is on 0.

I also reset all the 'resettable' options on my trip computer after re-fuelling. 

So I can only assume that it stores the data in the same way as the data for the gear change indicator.

If it does store all previous data, then I imagine it will use a 3 (approx) point moving average to determine the miles to zero. If it used fewer points the sample used would be inconclusive. If it used more the resultant value may not be representative. 

Below is a graph showing my average MPG for the last 7 fill ups and a 2, 3 and 4 point moving average used to predict my average MPG (and therefore miles to zero) for the 8th tank.

image.thumb.png.f33b15467dbde0c3d1bfe5337c76f701.png

As it happens, the predicted 41 MPG would give me a miles to zero value of 378 mi. When I filled up last it showed 381 mi. So, the 2 and 3 point moving average predictions are quite accurate, even despite the terribly unstable MPG data points!

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On 29/01/2018 at 8:54 AM, Tiexen said:

Be careful with doing that:


As the fuel level gets low the car will start picking up debris from the bottom of the tank. This can damage both the fuel filter and pump. The catalytic converter can also be damaged.

Most fuel pumps draw fuel from the bottom of the tank constantly so I don't think it makes much difference these days. Also, fuel is far cleaner then it used to be.

My biggest concern with running out of fuel would be the sudden and complete loss of power.

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i was going ask where does everyone think the fuel is drawn from? right at the bottom within a few mm in a recess normally. lol
and most debris in tanks used to be from rusty tanks years gone by before plastic tanks. ive had lots of plastic tanks dropped down inspecting pumps/senders and nearly all the occasions the tanks were spotlessly clean.
on my mazda6 i could go another 60 miles when it showed empty

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I broke my Hyundai Coupe for parts having done 160k miles in it over 13 years. When I removed the pump both the tank and in-tank filter (shown below) were as you say pretty much spotless.

CoupeFuelPump3.jpg

I must admit; I was actually quite surprised myself!

(Incidentally pretty much every fill-up I did in that car was from a near-empty tank as I religiously monitored its fuel consumption and so wanted to minimise calculation errors)

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On 1/30/2018 at 7:06 AM, dansallis said:

270 to 300 mpg! Damn son, I need one of those!! :cool:

Changed Lol ...Would of been good        :smile:

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On 1/30/2018 at 10:25 PM, iantt said:

.......... i could go another 60 miles when it showed empty

is that a challenge ?

big iantt is throwing down the gauntlet in the drive till empty contest........

game on !  ;-D

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