Hello. I drive a Ford Fiesta Mk.7 2010, petrol. All of a sudden, it has become outrageously uneconomical to run: I can't get more than 250-300 miles from a tank. I mainly use it within town limits, with very short stretches of ring roads. I drive as smoothly as possible, using steering, accelerator and brakes very gently. I took it to the garage, and they’ve found nothing obviously amiss. No visible leaks, no smell of petrol. Barring that, the car is totally fine and a pleasure to drive (as it has always been). I’ve been googling around – no joy. I’ve found only of a couple of very old posts here. Any clue? Many thanks in advance!

Alex

33 mpg or thereabouts in stop start town driving might not be outrageous. What was it doing before?  When was the car last serviced and which engine do you have?

 Can you push it? Binding brakes drink fuel.

Does the clutch slip? 

Are the tyre pressures correct?

40 minutes ago, A Pesaro said:

I drive a Ford Fiesta Mk.7 2010, petrol.

What engine?

40 minutes ago, A Pesaro said:

I can't get more than 250-300 miles from a tank

Are you getting this reading from "miles left to 0" or are you actually resetting the trip computer every time you brim the tank?

Has it had exhaust emission test done? Eg to see if it’s running rich due to oxygen sensor problems although if that was a problem I thought eml might be on

 

Its probably one of the oxygen sensors or worst case a leaky fuel injector (however I have never heard of this on Mk7 Fiestas)

may be worth plugging into OBD live data tool and seeing what each sensor is reading

 

Or most likely have you only started to notice this after a few tanks of E10?

Car was serviced and then MOT-tested in July. The anomaly became apparent a month ago or so. Consumption hovered around 40MPG then all of a suddenly went up. I became aware of it after noticing that I kept refueling it shorter and shorter intervals. I’ve the feeling it’s worsening: today the needle went noticeably down after a 10’ trip. Interestingly, on-board card computer is stuck to 40.1 MPG despite this being inaccurate.

"Are you getting this reading from "miles left to 0" or are you actually resetting the trip computer every time you brim the tank?"

I kept a fuel diary by averaging multiple 'quarter of tank' mileages. This was done by manually took note of how much miles I can get from the the first, second, and third quarter. I consistently got around 65. 

Try this: Estimate how much fuel is in your tank from the gauge then brim the tank. If it is rather less than you think it should be, the fuel gauge is faulty. The fuel computer is still giving the same reading as it was so I an sceptical of any real fault. Rule the gauge out. Drive a hundred miles then brim the tank again. Now you know how many gallons you need for 100 miles. Calculate. 

If the car was using significantly more fuel you would experience rough idling,  probably poor acceleration and misfiring  when pulling away and a warning of engine problems on the dash display. The tailpipe would be very black and either oily or sooty. A s you have not reported any of those symptoms (It runs well and the computer reads normally,) I'm going with the gauge. 

28 minutes ago, Neb_engineer said:

Or most likely have you only started to notice this after a few tanks of E10?

Fair point. Right when E10 leaflets were put out at CoOp...

E10 will not be causing a problem and anybody who suggests so is completely

WRONG!

If five per cent of the fuel had been taken out and not replaced, you would lose 2 MPG in 40.

It has been replaced with something about 80% as good as what was there before. The difference in consumption will therefore be a loss of no more than one per cent. 0.4 MPG. Far less than you will be able to read from a fuel gauge.

The only way to be sure of your actual mpg is to use the brim to brim method as @anon suggests and carefully calculate it yourself.

Regarding E10, I have now done well over 1,000 miles on it and have not seen any difference in mpg.

Same here- lots of miles on E10 and no difference in mileage or performance whatsoever.

It depends on the quality of E10, my car has felt a lot less powerful and uses about 1/8 of a tank more on journeys that used to take only 1/4, this was after changing from filling at asda to Sainsbury's

15 hours ago, Neb_engineer said:

It depends on the quality of E10, my car has felt a lot less powerful and uses about 1/8 of a tank more on journeys that used to take only 1/4, this was after changing from filling at asda to Sainsbury's

I normally use Tesco, but have also had E10 from Gulf and BP stations and no problem with any of them.

You can get "bad" fuel of any type of course, from a dirty storage tank etc. In all my years driving I've only experienced it twice though - many years ago from a NAFTA station and more recently a Morrison's site.

I usually buy mine from Asda because it's the cheapest, or Tesco as the next best bet. Never a problem.

19 hours ago, Neb_engineer said:

It depends on the quality of E10, my car has felt a lot less powerful and uses about 1/8 of a tank more on journeys that used to take only 1/4, this was after changing from filling at asda to Sainsbury's

It's strange how some folk are finding problems with E10 and others, myself included, can find no difference whatsoever.

2 hours ago, Bobr said:

It's strange how some folk are finding problems with E10 and others, myself included, can find no difference whatsoever.

It is. I don't know if I've missed any (there are several threads featuring E10 running now) but I don't think I've seen a case where someone who carefully monitors mpg (e.g. by the brim to brim method) has reported lower mpg. There have been several of the "I used to get "x" number of miles on £25 worth etc." variety which is not very precise when fuel prices are rising generally any way. 

Can't account for those who say their car "feels less powerful" though - I'm sure they're not imagining it, and I'm pretty certain I'd notice a loss of power in my car also.

Dyno run, anyone?

 

The Ecoboost is fuel sensitive. It is designed to be. I have tried a premium fuel once  (and when I did, it was much cheaper than E10!) 

The engine definitely seemed more responsive and I was not expecting it to so it is doubtful I imagined it.

I did not find any improvement in economy and I expect that the car adjusts the power in order to match the fuel.

That brings with it a question. My daily drive is a  minimum couple of miles. Maybe a single ten mile run per week and three or four of five.  I get 45-48 MPG over a tankful.

I rarely use all the performance, for no better reason than reducing paint chips. If I do, it will be for no more than half an hour and the journey will be under fifty miles.

Anything longer takes as long as it takes because over 200 miles, you don't get to forsee the traffic so I take my time and often see 65-67 MPG at an average 50.

The car is adaptive. It is happy to return these figures the way I drive and it does not vary with the fuel grade used to any significant extent.

It probaly keeps the wick turned up a bit more on harder driven examples. Does it then turn it down more for E10 than many of us are experiencing? 

I have not noticed any drop in performance or fuel economy, but have heard that E10 fuel could cause problems with the higher specification cars from other manufactures. 

Terry.

I keep a fuel diary on my laptop using the brim to brim method.   I have now been using E10 ever since it came out and I can see absolutely no difference in mileage.   Even with the very cold weather we've had lately I'm still getting 44 mpg.   There has been no change in performance either.

well i have now been keeping track of my MPG average after filling to the brim for several fill ups, most my driving is a mix between town and motorway, i have driven 60mph on the motorway, and there is about a 4mpg average difference between E10 and E5 (this is an average of 10 fill ups on either fuel), that being said above 60mph, the mpg average is a lot worse on E10 than E5, about 9- 10 mpg!!

52 minutes ago, Neb_engineer said:

there is about a 4mpg average difference between E10 and E5 (this is an average of 10 fill ups on either fuel), that being said above 60mph, the mpg average is a lot worse on E10 than E5, about 9- 10 mpg!!

It's very odd that some of us are finding a big difference and others not. My experience with both mine and my wife's SEAT Mii is the same as Bob's, similarly measured by the brim to brim method.

According to RAC fuel watch, the average for unleaded (E10) is 147.64ppl and for super unleaded (E5) is 160.43ppl, so almost 11% more. 

All of my cars have used more fuel when the weather gets colder