[Closed] What's happened to my mpg?

How are you arriving at the average? Are you going on the figures the car is reporting or are you getting all Peter Poddy about it and actually doing real sums? I tend to use hire cars a lot and usually for 1000mile motorway cruises and there seems to be some variation in the way they calculate their average and their responsiveness to changes in driving style/conditions. Some cars seem to be taking their average over quite a large range. I had a toyota earlier in the year and it took about 400 - 500 miles of gentle cruising before the reported average started to improve (it had presumably been used for a lot of town driving previously), after that it continued to rise steadily over the next 600 miles before I gave it back. It was reporting 32mpg when I got it and 49mpg when I handed it back after 1100 miles and was still climbing. So maybe the battery disconnect has introduced a blip that is still being accounted for in the average.

If the engine management system had been reset when the battery was changed then this can affect the engine but it shouldn't take long for the engine management system to 'relearn' the correct settings. Usually you just let your car idle for a bit.

Cold weather can affect economy as the lights and electric heated windows tend to be used more.

Do you reset your average fuel often, or do you leave it ofr long periods?
If you leave to get a true average, it will take a while to get back to the previous average
Because your battery has been changed the averages will have been reset

I'm simply going off the indicated mpg. I've only covered about 200 miles since the new battery went in so it might well be as you say and the EMS needs to re learn its settings. I'll see how I get on. Ta

Cold air is more dense the warm air...add that to the extra demand from heater, fans, and lights etc

The car is working harder also more fuel is used from a cold start in winter as it takes longer to reach temp>

or are you getting all Peter Poddy about it and actually doing real sums?

Brilliant!

Easygirl: occasionally the car might not move for a couple of days but no longer than that. Also I tend to reset the average whenever I refill and as I say I think the lowest it's ever returned is 32.6 over a full tank. I haven't changed my driving habits either and it's just a bit disconcerting to see such a marked drop.

I hope I don't lose anything in Manchester and have to rely on Bizzies to find it for me. 🙂

I wondered how long it would take for Dadly to turn up. 🙂

or are you getting all Peter Poddy about it and actually doing real sums?
Brilliant!

🙂 He does actually do that though and I think thats an important distinction because the cars own reporting can be bullshit.

Been up all morning Breggie. 😐

(Sorry, not much hep I'm afraid but hope you're well. 🙂 )

Maybe air filter, take it out and have a look.

Also could be a lambra sensor on its way out, or a sticking caliper.

Check the thermostat and temperature sensors. If the car isn't getting warm / thinks it isn't, then it will run a bit rich and this will put your fuel consumption up.

Brakes are fine, as above. Also new air filter fitted this week as part of the service.

I'll see how I get on over the next few hundred miles, am giving it a run down to the south east over Xmas so that should give a better indication.

DD, I feel for you but it does get easier in 5 or 10 years! 🙂

He does actually do that though and I think thats an important distinction because the cars own reporting can be bullshit.

I do and it is. Apart from that this is a very flattering thread. 🙂

Reasons I've found for reduced MPG include

Weather
When it's colder like it has been of late engines take a lot longer to warm up. Any journey of under about 20 miles will show this up. The longer the journey the less the effect because you spend less percentage of time running cold.

A change in route or use
This is the biggie as it effects everything. I've got a graph of something like 40,000 miles stored for out car and you can see average long term fuel consumption rise and fall over a period of months and I can tell you exactly why it happened.

Changes in the car
Not as in a different car but stuff like servicing, tyres etc. I noticed a slight improvement after we had the first new set of spark plugs. The engine was noticeably smoother and more responsive and this seemed to translate into better MPG. Eco tyres didn't seem to make the slightest jot of difference but pressures do, slightly. Retro fitting cruise control made ours worse. That, I think, is partly because its not as sensitive as an OE system and partly because I'm one flippin' light footed bar steward and I can beat the cruise at its own game.

Personally, for the OP, I'd say there's a slight chance it's a mechanical issue but more like the fact that this happens all the time, but not being a geek (hello!) you've mover noticed it before.
I'd be tempted to say its the weather to be honest. 🙂

b r - Member

Maybe air filter, take it out and have a look.

Also could be a [b]lambra[/b] sensor on its way out, or a sticking caliper.

Is that a Freudian slip, revealing br's sexy ovine tendencies? 😕

I've got a graph of something like 40,000 miles stored

I fear I have opened Pandora's box!

Everything PP says, but a big WTF!!! to "low to mid 30's" as an acceptable average 🙂

Eco tyres didn't seem to make the slightest jot of difference but pressures do, slightly

Eco tyres made a big difference for me on the Passat, but not on the Prius, but I think the tyres that it came with may have been somewhat eco orientated (although they were not great tyres).

I went from about 53mpg on my regular long route to about 58mpg, so around 10%. That was moving to Nokian H for summers and Nokian WR G2s for winter tyres, from Dunlop Sport.

Cruise control helps me, but not because it's light footed. Consistent speed helps a lot ime if you actually are cruising, not if you are on windy hilly routes.

But this is not what the OP asked. Presumably he's doing everything the same, whether that's good or bad, but the mpg has suddenly dropped. Not sure why tha tmight be tbh but I'd guess some kind of engine sensor or injector problem or something. But then you'd expect any sensor issues to get flagged up.

Here you go. Off a phone app called Road Trip

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[url= http://www.flickr.com/photos/peter_atkin/8276720917/ ]Untitled[/url] by [url= http://www.flickr.com/people/peter_atkin/ ]PeterPoddy[/url], on Flickr

The first big rise (look at the average line, not individual figures) is from when we drove the car over a snowy winter to me driving the same route along the M4 back and forth to Bristol. Then it dips slightly as I come off that same route and switch to more varied driving, then the car gets left at home more and does a 20 mile run to reading and back it dips a bit more, but it's still used for several longer journeys. The last few tanks have been frm when it's being doing a regular 20 mile commute on A/B roads in cold icy weather. That's killing it.

EDIT
Stats were reset on 9th November. The first three figures in 2010 are from 21 November, 6 & 24 December. Wasn't it snowy then?
Look at it jump after then

Been listening to any new music?

30,000+ miles a year! 😯

Edit: 15,000 miles a year 😳

That's 2 years, dates at the bottom. I was driving for work though. You can add 8500 miles to that.

You wanna be TRULY shocked by a statistic?
Check this out, under the FUEL section, bottom left....

[url= http://farm9.staticflickr.com/8502/8276757323_31d329f3e6_b.jp g" target="_blank">http://farm9.staticflickr.com/8502/8276757323_31d329f3e6_b.jp g"/> [/img][/url]
[url= http://www.flickr.com/photos/peter_atkin/8276757323/ ]Untitled[/url] by [url= http://www.flickr.com/people/peter_atkin/ ]PeterPoddy[/url], on Flickr

And then add this to it

[url= http://farm9.staticflickr.com/8216/8277820542_7e3f3620c4_b.jp g" target="_blank">http://farm9.staticflickr.com/8216/8277820542_7e3f3620c4_b.jp g"/> [/img][/url]
[url= http://www.flickr.com/photos/peter_atkin/8277820542/ ]Untitled[/url] by [url= http://www.flickr.com/people/peter_atkin/ ]PeterPoddy[/url], on Flickr

Just under £6800 in fuel in 2 years
Oh plus the the two bikes, another £1700 between them.

£8500?

That's why I'm anal about fuel.

But how do you know that data is right?

PP thats quite good 😳

I used to have a Discovery I was doing 45000+ a year in - stick a one infront of your fuel cost for the bill 😯

It's now gone..............

But how do you know that data is right?

Because I collected it using the most accurate figures available over a large number of samples spread over a large sampling time. Without fitting a calibrated speedo its impossible to be more accurate.

I have to point out the Omega. That mileage was in just over 3 months, the car was an old, high mileage 2 lite auto that cost £400. I spent £100 in repairs on it, I reckon it saved me £70 in tyre wear on the Focus above it and £75 for a new tyre when I got a piece of steel through one tyre that I didn't replace, then we got £170 scrap for it. Less than £200 that car cost me, excluding fuel 🙂

You wanna be TRULY shocked by a statistic?
Check this out, under the FUEL section, bottom left....

I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around £150, so that vaguely averages to £54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.

druidh - Member

Everything PP says, but a big WTF!!! to "low to mid 30's" as an acceptable average

Driving pleasure is directly proportional to fuel consumption. 💡

😈

[quote=maccruiskeen ]You wanna be TRULY shocked by a statistic?
Check this out, under the FUEL section, bottom left....
I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around £150, so that vaguely averages to £54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.
How many Wales's is that?

I'm currently averaging 16mpg! Don't know how good you have it you lot 😀

How many Wales's is that?

exactly one Wales, if you spread the Co2 0.00385mm thick

I recently worked out that my van had been through 54,000 litres of diesel (666 tanks of fuel) when it passed its 300,000th milestone The first of those litres would have cost 77p the most recent around £150, so that vaguely averages to £54k. Thats 144 tons of CO2 which is about 80,000m3 which is approximately the volume of the Albert Hall.

Lovely. GEEK TO THE MAXXXXXXXXX! 😉

How many Wales's is that?

That 2l Omega lump did quite well on fuel compared to your much newer Focus (1.6l IIRC). Shows how crap the Focus (and many other newer cars) is really.

Shows how crap the Focus (and many other newer cars) is really

Not really. The type of drive varies which skews the averages and the Focus still comes out ahead.

Moly, you must be very clever to extract that conclusion from the data shown...

However, yes it comes out ahead. But, a knackered old lump (PP in this case 🙂 ) in an old auto Omega is only ~4mpg better than a much newer, manual 1.6l Focus?

You'd have thunk the gap would be biggerer no?

You'd have thunk the gap would be biggerer no?

cars keep getting heavier though so older cars perform better than you'd imagine for their older tech, the new ones are are pulling more weight around. I think the current fiesta is double the weight of the first ones.

PP told us that the type of driving varied.

As for the gap - well 10% isn't insignificant, but we also don't have as much data for the Omega as the Focus. The Omega could have been used on more economical routes for all we know. And Poddy's average was higher until he changed his driving pattern recently, as he told us. It was up about 43 or so last time this came up IIRC which is 10% difference.

I think 35 is pretty good for the Omega, but I think 40 or even 43 isn't great for the Focus. But again, Poddy is into this stuff so I would assume that the journey profiles aren't great. Then again, his best tankful is only 45.

To wave the flag for newer cars, my auto Passat is faster than that old Omega, has many more safety features and gets 60mpg on a good run. So ner 🙂