"Fuelly" application thing

[Welly]

Thought I'd try this Fuelly thing and it was easy enough to set up. I'm confused as to how it estimates the MPG though (unless I'm being thick).

Example: I fed in the last two partial fills, one yesterday, with estimated mileage (fairly close as I could) just to get it going. But what if I sloshed in another £35.00 or so today, with mileage, it'd think I've used that much fuel in one day but haven't traveled far? have you got to BRIM the tank each time?? (I don't like doing that).

[jonsowman]

If you want it to track mpg, then yes, you need to brim the tank every time. A partial fill will mean it'll avoid calculating mpg for the driving on either side of the partial fill. It's only between consecutive full fills that it calculates mpg.

It still has a useful for partial fills: it lets you track how much you're spending and is a more accurate record of the miles you drive.

For my old D8:
http://www.fuelly.com/driver/jonsowman/406

[Welly]

Mmm, of course, it can't know how much fuel you've used between partial fills so it must estimate and assume the quantity of fuel is 'actual'.

I don't like a full tank, firstly the weight of it but the eye-watering cost is a put off (a bit blinkered and I know if you're paid monthly then you're gonna spend the money on fuel regardless) I think I'd have to get rid of it if I kept brimming the tank! I'd rather stay in my half-tank world of being at least partly unaware of the real cost. I guess in reality I spend £35.00 to £40.00 per week? I guess I'll find out soon

[jonsowman]

I'm the same, I try and keep the tank around the 1/3 to 1/2 mark - it's 70 litres so carrying around a full tank is a bit like having another person in the car all the time! Also the cost is indeed eye-watering.

I started using Fuelly to try and monitor whether the trip computer mpg estimates were accurate, and since I've found they mostly are, I've stopped bothering a bit.

Still, it's a very neat app and a good way to keep track of miles and spending.

[scotty73]

Since i started using it I've got in the habit of filling up once a week plus these days that's how we budget... I gradually got it to full and now i just top it up to first click every week.

Thing is I stopped updating fuelly over 6 months ago but still keep a full tank just in case...... Just in case what? what in my head is going to happen that i suddenly need upto 1000 miles of fuel?

[Welly]

That's what I meant before; you're lugging over 70Kg's around. I also see a full tank as having a money value; if the car gets written off or nicked or the tank gets drained it's a lot of money to lose.

Conversely though, and in scotty's case if you find yourself a bit 'Bobby Flint' you've already banked the fuel so can use it to tied you over a few weeks maybe.

[scotty73]

Conversely though, and in scotty's case if you find yourself a bit 'Bobby Flint' you've already banked the fuel so can use it to tied you over a few weeks maybe.

I think that is why i do it I'd hate to have £100 in diesel sat outside the door if the car was fooked though and feel even worse if some lil scroat drained it for their gains but it's there if one week i cant afford to top up or as the case has been this year my nan is a 400 mile trip away and i could go get her with the fuel i got in there no worries without her having to wire money to me... Heaven forbid she ever had to do that.

And then there's all these fuel strikes we get.

[mjb]

That's what I meant before; you're lugging over 70Kg's around.

The cost of this is actually negligible as long as you're not doing a hundred 0-60s a day. Even so, the cost saving by running an empty tank is likely obliterated by having to go to the petrol station more often...

Diesel around 850g/litre, so 60KG a tank (although diesel can vary a few percent as the blend changes depending on the season). A manual 2.0 HDI110 saloon weighs 1410KG, and at 30mph (13.41m/s) has 0.5*mv^2 = 127KJ of kinetic energy (defined as the amount of energy required to move the object to the given speed from a standstill). Add 60KG to that and you end up with 132KJ - 4% more energy.

Now, that's assuming the engine is 100% efficient (diesels are around 40% efficient, petrol 25-30%), but the ratio - 4% - is roughly right. This is of course dependent on the engine maintaining constant efficiency throughout acceleration, which is impossible to work out theoretically as it's dependent on condition and then how fast you accelerate due to the non-linear nature of fuel consumption where turbochargers are involved...

But yeah, I'd go with the 4% figure. Now, that's only accelerating. When cruising at a similar speed, the only difference (due to wind resistance not changing) comes from increased rolling resistance due to the tyres squashing out more at the bottom. This is negligible at speed. When decelerating, if you come off the accelerator earlier, you can recoup some of that 4% due to the extra momentum.

Now, diesel has an energy density of 35.86MJ/litre, so needs (127/35860)/.4=8.85ml to accelerate to 30mph unlaiden at 40% efficiency, or 9.20ml with a full tank. At petrolprices.com's average of 137.78p/litre today, that's a price difference of... 0.05p (1.22p vs 1.27p) each time you do 0-30.


The energy for a 0-30 in a petrol (32.18MJ/kg, 737g/litre for 92RON) BMW 540i touring (1815KG, presuming 25% efficiency) is 163KJ unlaiden and 168KJ with a full 70 litre (52KG) tank, (163/32180)/.25= 20.26ml, (168/32180)/.25=20.88ml. At 130.46p/litre, that's a price difference of 0.1p (2.64p vs 2.74p). Interesting. To me... Wish I could find the volumetric energy of Shell V-Power

[Welly]

You love a challenge don't you mate impressive reply!

[GingerMagic]

That is by far the most in-depth reply I have ever read......

I just put £75 in the tank, and then again when the light comes on.

I will do the fuelly thing later, I have a fuel log app on my phone which shows my car costs 13p per mile to run...

[DaiRees]

That's what I meant before; you're lugging over 70Kg's around.

The cost of this is actually negligible as long as you're not doing a hundred 0-60s a day. Even so, the cost saving by running an empty tank is likely obliterated by having to go to the petrol station more often...

Diesel around 850g/litre, so 60KG a tank (although diesel can vary a few percent as the blend changes depending on the season). A manual 2.0 HDI110 saloon weighs 1410KG, and at 30mph (13.41m/s) has 0.5*mv^2 = 127KJ of kinetic energy (defined as the amount of energy required to move the object to the given speed from a standstill). Add 60KG to that and you end up with 132KJ - 4% more energy.

Now, that's assuming the engine is 100% efficient (diesels are around 40% efficient, petrol 25-30%), but the ratio - 4% - is roughly right. This is of course dependent on the engine maintaining constant efficiency throughout acceleration, which is impossible to work out theoretically as it's dependent on condition and then how fast you accelerate due to the non-linear nature of fuel consumption where turbochargers are involved...

But yeah, I'd go with the 4% figure. Now, that's only accelerating. When cruising at a similar speed, the only difference (due to wind resistance not changing) comes from increased rolling resistance due to the tyres squashing out more at the bottom. This is negligible at speed. When decelerating, if you come off the accelerator earlier, you can recoup some of that 4% due to the extra momentum.

Now, diesel has an energy density of 35.86MJ/litre, so needs (127/35860)/.4=8.85ml to accelerate to 30mph unlaiden at 40% efficiency, or 9.20ml with a full tank. At petrolprices.com's average of 137.78p/litre today, that's a price difference of... 0.05p (1.22p vs 1.27p) each time you do 0-30.


The energy for a 0-30 in a petrol (32.18MJ/kg, 737g/litre for 92RON) BMW 540i touring (1815KG, presuming 25% efficiency) is 163KJ unlaiden and 168KJ with a full 70 litre (52KG) tank, (163/32180)/.25= 20.26ml, (168/32180)/.25=20.88ml. At 130.46p/litre, that's a price difference of 0.1p (2.64p vs 2.74p). Interesting. To me... Wish I could find the volumetric energy of Shell V-Power

Shyte, I was just going to say that lol

Now I fill it to full then drive it until the light comes on (unless I've got a long journey planned then I might fill it back up sooner. I do this because my fuel station choice is conditioned by a combination of cost and quality, and not of the ones I "like" are conveniently on my daily run, so to drive to one more often than I absolutely have to would cost me fuel. I know it costs the best part of a ton to fill it but it's not actually going to cost / save me any money because I'll still end up using the same amount of money over the same time, so really it's just a money management issue.

I've been using the Fuel Log Android App too, it's excellent, calculates all your usage and costs (including other costs as well as fuel costs) and gives you loads of stats and graphs, including stuff like fuel costs per mile and per time period, accumulated costs, fill volumes, and a record of your car's milage over time. I noticed this interesting stat the other day...

[Welly]

Maybe I'm spoilt a bit by working a stones-throw from a Tesco Momentum dispensary......I'm quite a familiar face round there

[steve_earwig]

(although diesel can vary a few percent as the blend changes depending on the season)

You hope The word on the Cross-Dresser forums this week is stay away from supermarket fuel as somebody just had their fuel filter block up with wax (and were charged 160 squid for recovering it and sorting it out).

I always brim my tank because I'm too lazy to make a detour to fill up and usually end up doing it in a panic because the light's been on for 2 days. And then it's so nice to look at a gauge pointing at the other end of the dial for a while.

Which reminds me, I didn't check the oil in the yoyo since... umm... I can't even remember where the dipstick is, does this make me a bad person?

[mjb]

That is by far the most in-depth reply I have ever read......

You don't read many of my replies, do you?

The word on the Cross-Dresser forums this week is stay away from supermarket fuel as somebody just had their fuel filter block up with wax (and were charged 160 squid for recovering it and sorting it out).

Thankfully I've educated the mrs on the evils of supermarket fuel and how it's a false economy (it definitely was on my tubby and I haven't bothered checking since...). Mind you, it's usually me that gets lumped with filling that damn thing up - she might make the odd £20 deposit, but leaves it to me to spend a ton at Shell

Also, don't forget you devil-fuel worshippers, regular top-ups can be very bad for the wallet if you have a FAP and a car that dumps liquid gold (eolys) into your fuel tank every time you remove the cap

[steve_earwig]

devil-fuel worshippers

(diesels are around 40% efficient, petrol 25-30%)

That's a point about the fap though, remember that lady 2.2 HDi owner (Amron?) that came on here with a dead car because she'd been just putting a little fuel in all the time and the car wouldn't run on a 50/50 diesel/eolys mix?