MPG conundrums

Jesus.

Does anyone else ever find their MPG calculations ofttimes not making much sense? For example, my last tank cost 94 Euro, got 13.18 Gallons into it and got 538 miles from it. That works out at 40.8 MPG. The fuel light was on too when I got to the station.

Now, two weeks later at the same Station, I've filled up with 93 Euro, but I got more fuel into it (13.29 Gallons) even though the fuel light never came on but I only got 497 miles from it. That works out at 37.4 MPG. Its almost 3 and a half MPG less than the last time even though, if anything, I drove the car easier this time round!

As far as I know, the price hasn't gone up nor down. Neither the amount of fuel that went in nor the mileage adds up for me. Maybe the auld bus just isn't as efficient as I thought it was!

Toyotafanboi

those are small enough variations. i'd be pleased with consistancy like that tbh.

when the fuel light comes on isn't at exactly the level every time, its an estimation.

Jesus.

Toyotafanboi wrote: »

those are small enough variations. i'd be pleased with consistancy like that tbh.

Does yours vary even more, fanboi?

when the fuel light comes on isn't at exactly the level every time, its an estimation.

That's true but the needle didn't appear to be down as far as last time either. But I suppose the needle is just an approximation too at the end of the day.

Toyotafanboi

ah yeah, i'd fairly religiously (excuse the pun :P) brim the tank and then drive it until the fuel light. always get in the ballpark of 600km's to the tank. could get 650, could get 550, could take 70 to fill, could take 80, but its always in the same ballpark.

figures will never be identical tank to tank, with variations like traffic, travel time, weather, load in the car, exact trips made etc.

Jesus.

Toyotafanboi wrote: »

ah yeah, i'd fairly religiously (excuse the pun :P) brim the tank and then drive it until the fuel light. always get in the ballpark of 600km's to the tank. could get 650, could get 550, could take 70 to fill, could take 80, but its always in the same ballpark.

figures will never be identical tank to tank, with variations like traffic, travel time, weather, load in the car, exact trips made etc.

You're spot on RE the variations. There's an awful lot of variables when you think about it. In that respect, you're never going to get it spot on no matter what you do.

Bpmull

Did you buy the petrol in the same place. The quality of the petrol diesel would have a big impact. I've bought diesel in a few unbranded places and put it in the focus and it would basically burn of the tank of diesel as fast as it could I could loose 100 km to a tank. So I found one branded place in Kilkenny that's more expensive than the rest but gets me the furthest my mpg are fairly consistent they vary between 50-54mpg which I would consider fairly consistent the car will never do the exact same mpg from tank to tank.

dgt

Different stations sell different quality stuff, it shows at times. My car usually averages in or around 45mpg, I'm happy with that. All different styles of driving whether its motorway, rush hour Dublin or tippin about the backroads also have to be factored in

Jesus.

Aye, I always fill up in the same Station lads. Its the cheapest in my general area, currently at 1.54 (as in 1.53.9!).

I was well happy with the 41 MPG I calculated the first time. A bit disappointed with the 37.5 I got today! But as the lad above said, there's an awful lot of variables to contend with. If I can keep her in the late 30's I'm not doing too bad.

jimgoose

I started out averaging 19.5 MPG in my car when I bought it in 2006. Now, that's up to 23.5. The thing seems to be improving with age, like a good whiskey. I do run a slightly lighter oil in there than OE, but still... not that I'm complaining or owt!

ironclaw

Its not really that big a conundrum.

13.18 Gallons x 40.8MPG = 537.74 miles

13.29 Gallons x 37.4MPG = 497.046 miles.

So about 8% in the difference. I doubt anyone has a route and driving style that could consistently stay within 10% of normal. Traffic alone would be too large a variant. If you dropped to say 30MPG (About 398.7 miles total) you'd still only be down about 25% on your 'best' MPG figure. Large movements of MPG don't necessarily equate to massive losses or conversely savings.

Jesus.

It does make a mockery of the on-board Computer though that told me I was getting 40-odd!

Toyotafanboi

hardly. you got "40 odd" on your first fill and very slightly less on your second.

Jesus.

Toyotafanboi wrote: »

hardly. you got "40 odd" on your first fill

Indeed, when it was telling me I was getting 40 odd.

and very slightly less on your second.

37.5 when it was telling me I was on over 40 all the time. Not very accurate the second time round.

Gumbo

Jesus. wrote: »

You're spot on RE the variations. There's an awful lot of variables when you think about it. In that respect, you're never going to get it spot on no matter what you do.

You can get. More accurate calculation by using the one click fill method.

Fill tank until nozzle clicks and stops.
Note mileage.
Drive car as normal.
When filling again, note mileage done and litres put in to one click fill and it will be more accurate than using the needle or yellow light as a guide.

Jesus. wrote: »

Indeed, when it was telling me I was getting 40 odd.



37.5 when it was telling me I was on over 40 all the time. Not very accurate the second time round.

It's an average value since you last reset the computer.

Jesus.

That's what I did mate!

Bpmull

Did you reset the average mpg when you filled the tank it's the only way it will be somewhat accurate is if you reset it every time you refill the tank.

Mint Sauce

Brim to red light.

44-48litres to fill. (53l tank)

Low 500 to high 600kms

67-79 euros to fill

(based on 09/12 to date)

Thats a big ball park.

Jesus.

jimgoose wrote: »

I started out averaging 19.5 MPG in my car when I bought it in 2006. Now, that's up to 23.5.

Christ, she's thirsty. What motor have you got Goose?

irish-stew wrote: »

Brim to red light.44-48litres to fill. (53l tank)
Low 500 to high 600kms67-79 euros to fill(based on 09/12 to date)
Thats a big ball park.

What car do you drive Stew?

(Bpmull, yes I reset the counter when I filled up alright.)

jimgoose

Jesus. wrote: »

Christ, she's thirsty. What motor have you got Goose?

S-Type Jag 3.0l V6.

Jesus.

jimgoose wrote: »

S-Type Jag 3.0l V6.

Well that explains it!

235 bhp?

highdef

I've changed my driving habits. I used to think I was doing well to get 800km per tank @ approx 6.3l per 100km. I managed to get it to approx 5.9/6l per 100km and about 850km per tank. Lately I've tried more (still without driving like a granny!) and I am on my record distance for a tank. I am at 919km and the computer says I have 35km left so if I was to run until near to estimated empty, I would have done about 950km at an estimated 5.7l per 100km. This is in a 2009 1.8tdci Focus. Always go to Topaz and usually the same branch.

So just by driving a little bit more efficiently, I have improved economy by about 20%, in terms of distance covered per tank of diesel.

jimgoose

Jesus. wrote: »

Well that explains it!

235 bhp?

Oooh yeah. :cool:

anthony4335

I used to get 29/29mpg consistently on my old 95. my driving habits and journeys were very consistent. However in one week I was down at 20mpg for apparent reason. The only thing I could think of was that I used a different petrol station that week so I assume I got a bad tank of fuel.
However gone are those days now ,57/58mpg so far with the prius. I hate that bloody bar graph makes me drive like a granny but I cannot help myself I have to have it on to squeeze ever last meter per km out of the tank.

Bpmull

highdef wrote: »

I would have done about 950km at an estimated 5.7l per 100km. This is in a 2009 1.8tdci Focus. Always go to Topaz and usually the same branch.

So just by driving a little bit more efficiently, I have improved economy by about 20%, in terms of distance covered per tank of diesel.

What size tank is in it in terms of litres or how many litres would it takes that seems good going for a 1.8tdci.

highdef

I think it's a 53 litre tank. Interestingly, if I do the sums of 5.7l per 100km, this adds to more litres used than the capacity of the tank. However, I think it is actually nearer 5.6l per 100km which still does not quite add up.
Either way, I'd be more inclined to trust the amount of kilometres the car says it has done rather than how much fuel it estimates to be burning.
Oh, and the car is completely stock, including wheels.

Jesus.

anthony4335 wrote: »

I hate that bloody bar graph makes me drive like a granny but I cannot help myself I have to have it on to squeeze ever last meter per km out of the tank.

I'm the very same. I'd love to turn it off and just drive as I like but I can't help it!

Mint Sauce

Jesus. wrote: »

What car do you drive Stew?

Astra GTC 1.4

Getting in or around the Book MPG based on the fuel diary. Although can drop quite a bit if only doing the daily commute between fills

Jesus.

Jesus. wrote: »

Does anyone else ever find their MPG calculations ofttimes not making much sense? For example, my last tank cost 94 Euro, got 13.18 Gallons into it and got 538 miles from it. That works out at 40.8 MPG. The fuel light was on too when I got to the station.

Now, two weeks later at the same Station, I've filled up with 93 Euro, but I got more fuel into it (13.29 Gallons) even though the fuel light never came on but I only got 497 miles from it. That works out at 37.4 MPG. Its almost 3 and a half MPG less than the last time even though, if anything, I drove the car easier this time round!

As far as I know, the price hasn't gone up nor down. Neither the amount of fuel that went in nor the mileage adds up for me. Maybe the auld bus just isn't as efficient as I thought it was!

Just filled up again. Down to 36.5 MPG now. That's a wee bit on the thirsty side considering the cost of fuel these days. I hope it bottoms out at this level and doesn't drop further!

Jesus.

Having driven as frugally as possible on the last tank, I squeezed out 41mpg (mixed). This time I decided to let her rip and see what the difference was. Well it turned out I got 33mpg this time around. That's a fair difference over a tank of petrol - about a hundred miles if I'm calculating it correctly.

Do y'all drive whilst counting the pennies or do y'all just not worry about it and drive the way you feel comfortable?

Bpmull

Jesus. wrote: »

Having driven as frugally as possible on the last tank, I squeezed out 41mpg (mixed). This time I decided to let her rip and see what the difference was. Well it turned out I got 33mpg this time around. That's a fair difference over a tank of petrol - about a hundred miles if I'm calculating it correctly.

Do y'all drive whilst counting the pennies or do y'all just not worry about it and drive the way you feel comfortable?

That's fair going. I couldn't see how you'd get anymore than 41mpg out of a petrol Laguna. As for checking consumption. I'd generally check the mpg every 3 tanks or so. I always let the tank go to half full or 1/4 and refill to brim so it's easy enough to calculate. The one thing I would keep an eye on is what distance I'm getting out of the tank so I reset the trip every tank (provided I remember to ) at the moment I'm getting 54mpg so I can't complain but that's mainly long trips and I don't drive the rag out of it well not all the time anyway.

pred racer

Jesus. wrote: »

Having driven as frugally as possible on the last tank, I squeezed out 41mpg (mixed). This time I decided to let her rip and see what the difference was. Well it turned out I got 33mpg this time around. That's a fair difference over a tank of petrol - about a hundred miles if I'm calculating it correctly.

Do y'all drive whilst counting the pennies or do y'all just not worry about it and drive the way you feel comfortable?

Every time I fill up I say " right, for this tank I'm gonna drive easy and see what she'll do" .........
Then I meet a felter/boyracer/oap/nice road/good song on the stereo/insert other reason to boot it, and it never happens:o

Jesus.

Bpmull wrote: »

I'm getting 54mpg so I can't complain

What Motor you got, Bpmull?

Got to be a diesel at those figures

(Or a Prius!)

lomb

Driving is so expensive anyway that 500 more in fuel to drive like you want to wont make any difference.
As the cars get newer the amount spent on fuel/tax is less but maintainance and depreciation is more.

Ive been reading over on pistonheads someone buying a s320 cdi for 3 grand and getting 45 mpg in complete comfort looking at everyone in their expensive shoeboxes getting less!

gallag

I never really check what my mpg is, won't change anything, some of you guys seem obsessive lol worrying about 3mpg tank to tank? Fuel diarys haha

Bpmull

Jesus. wrote: »

What Motor you got, Bpmull?

Got to be a diesel at those figures

(Or a Prius!)

1.6tdci focus tbh I can never remember getting less than 50 mpg when checking it. So it generally varies 50-54mpg I couldn't see myself getting anymore than that out of it. It's funny because you think 54mpg is great but it feels like I'm always putting diesel in it :pac: I think I just drive to much. I suppose when you get use to the mpg your car does you think nothing of it my last one was doing 50mpg so this was is definitely a bit lighter on fuel.

Donnelly117

Jesus. wrote: »

(Or a Prius!)

SHHHHHH!!!!! He'll hear you...

As for driving fast/economical as long as the average MPG stays above 30 im happy!

overshoot

iv managed to get a bit over 1200km to the tank (Top), usually comes in 11XX km, lowest 1030 (Texaco) but too many short trips in that one.
brim it and get a bit over 53L in every fill and run til the range is 0.

more an experiment to see if theres a difference between garages now iv got me first car, heavy foot if the mood takes me, but wont kill myself trying to clear a serious q of cars either. if im briming it i just reset the trip clock for the sake of it, may as well use it for something
5.2/5.3L/100km lifetime average, moves between them (54mpg). previous owner got 48mpg out of it, (reset it when i got it).

Sam Kade

I use the same filling station most of the time 1 fill I managed to put 66 l in a 64 l tank which never before happened. If that was the case I should have pushed the car onto the forecourt.

ifeelstupid

I hate letting the needle go much below half way mark and usually fill to rounded off litre after first click around then keeping a note of amount of diesel and mileage - all in the head I know but it feels easier to pay weekly fuel in 2 goes than in one big fill. Over last 1200 miles I averaged around 49.25 mpg, it was closer to 52mpg until I encountered the wrath of St Anthony in Galway last week and spent around 90 mins mainly stuck in traffic:(
Just wondering if you think I am getting reasonably accurate readings even though I don't let the tank run down so low?

Thanks

Jesus.

lomb wrote: »

Ive been reading over on pistonheads someone buying a s320 cdi for 3 grand and getting 45 mpg in complete comfort looking at everyone in their expensive shoeboxes getting less!

That's mad isn't it? Of course his tax would be very high but he's already made that back by getting it so cheap - providing its in good nick of course. Just goes to show that if you use your noggin, you can still get half decent value out there.

I fill up in Coolquay about once every 3 weeks. Its currently the cheapest place in my part of the Country (Fingal) as far as I can see. Got it at 149.7 (petrol) yesterday.

MuppetCheck

ifeelstupid wrote: »

I hate letting the needle go much below half way mark and usually fill to rounded off litre after first click around then keeping a note of amount of diesel and mileage - all in the head I know but it feels easier to pay weekly fuel in 2 goes than in one big fill. Over last 1200 miles I averaged around 49.25 mpg, it was closer to 52mpg until I encountered the wrath of St Anthony in Galway last week and spent around 90 mins mainly stuck in traffic:(
Just wondering if you think I am getting reasonably accurate readings even though I don't let the tank run down so low?

Thanks

The level in the tank doesnt matter once you are calculating it the same way.

Miles driven
Litres to fill converted to gallons
Then divide the miles by the gallons

There's loads of handy free apps for phones that will do it for you these days. I just log the fill up before I move off.

Jesus.

Does anyone else notice their fuel economy going down a wee bit since the cold weather set in?

Is that to do with the car taking longer to warm up?

Also, I have my heater on pretty much every day now. Does powering the fan use up more juice? Is it run off the battery?

MuppetCheck

Anything you use in the car will use more fuel. Heater, lights, wipers, demister, heated mirrors, air conditioning etc all use more juice.

Jesus.

I suppose that makes sense Muppet. The battery would need constant charging by the Motor.

Putting the heater aside for a minute, she'd still use more fuel this time of year because of the cold, wouldn't she?

Lissavane

Jesus. wrote: »

Does anyone else notice their fuel economy going down a wee bit since the cold weather set in?

Is that to do with the car taking longer to warm up?

Also, I have my heater on pretty much every day now. Does powering the fan use up more juice? Is it run off the battery?

Seems like the FEF (free energy fairy) has failed. It rarely happens but if it does you're fvcked.

MuppetCheck

Jesus. wrote: »

I suppose that makes sense Muppet. The battery would need constant charging by the Motor.

Putting the heater aside for a minute, she'd still use more fuel this time of year because of the cold, wouldn't she?

Fuel won't burn as easily, takes longer to heat up too. So yeah, there's a few different factors at play.

dr.fuzzenstein

Jesus. wrote: »

Does anyone else ever find their MPG calculations ofttimes not making much sense? For example, my last tank cost 94 Euro, got 13.18 Gallons into it and got 538 miles from it. That works out at 40.8 MPG. The fuel light was on too when I got to the station.

Now, two weeks later at the same Station, I've filled up with 93 Euro, but I got more fuel into it (13.29 Gallons) even though the fuel light never came on but I only got 497 miles from it. That works out at 37.4 MPG. Its almost 3 and a half MPG less than the last time even though, if anything, I drove the car easier this time round!

As far as I know, the price hasn't gone up nor down. Neither the amount of fuel that went in nor the mileage adds up for me. Maybe the auld bus just isn't as efficient as I thought it was!

I decided a long time ago that to convert liters into gallons and km into miles was an awful complicated way to figure out my fuel consumption.
I'd be sitting there with a calculator for two hours.
Here's the simplest way:
Drive till fairly empty. Fill up till it clicks off. Zero km counter.
When you fill up next time, take note of recorded "mileage" (because kilometerage sounds strange, even to me) and how many liters went into the tank.
So:
720 km
45 liters.
45 divided by 7.2 = 6.25 liters per 100 km.
All you have to do is divide the amount of fuel by (km driven divided by 100).
It takes me 10 seconds to work out on my phone once I glance at the liters on the pump and the mileage displayed, I know how much my car uses before I've even paid for my fuel.

For some reason I always get chairs thrown at me as soon as I mention l/100 km, I have no idea, people seem to like medieval measurements...
/ducks

jimgoose

MuppetCheck wrote: »

Fuel won't burn as easily, takes longer to heat up too. So yeah, there's a few different factors at play.

Colder air is denser as well, so modern EFI setups will inject more fuel to maintain stoichiometry. The upshot of this is a tad more power.

jimgoose

dr.fuzzenstein wrote: »

...For some reason I always get chairs thrown at me as soon as I mention l/100 km, I have no idea, people seem to like medieval measurements...
/ducks

Eee, you can feck of with yer weird foreign muck!!

dr.fuzzenstein

jimgoose wrote: »

Eee, you can feck of with yer weird foreign muck!!

Usually someone mentions rods to the hoghead by now.:D

Jesus.

MuppetCheck wrote: »

Fuel won't burn as easily

Which would require more fuel to be pumped through I suppose?