Worse than expected fuel economy 1.4TDI

[Mk4]

I have a 2007 Ibiza 1.4tdi sport 80ps, which according to parkers should get around 60mpg average based on I think a 70/30 town motorway driving split.

However, on my last full tank I probably did about 70% motorway driving and my mpg across the tank (approx 500 miles) was 51mpg, measured using the brim to brim method and fuelly.

I don't thrash the car at all, I regularly coast up to junctions and I would say am generally an economical driver. I know these figures are often over exaggerated by the manufacturer, but I've seen guys with the 1.9 FR claiming a better mpg.

Any ideas of the cause? Or any potential solutions?

Would cleaning the turbo, egr or particulate filter help?

 

[Lowe]

Manufacturers figures are optimistic unless under perfect conditions.

On a side note, coasting up to junctions costs you fuel - you're disconnecting the engine from the transmission, so the engine has to use fuel in order to idle. Keeping in a high gear and just coming off the throttle doesn't - the inertia of the car keeps the engine turning over instead.

 

[Mk4]

Manufacturers figures are optimistic unless under perfect conditions.

On a side note, coasting up to junctions costs you fuel - you're disconnecting the engine from the transmission, so the engine has to use fuel in order to idle. Keeping in a high gear and just coming off the throttle doesn't - the inertia of the car keeps the engine turning over instead.

I know they're always optimistic, but if they're saying an average of 60 in majority town driving, it seems odd being 10mpg short with majority motorway journeys. I have also seen others suggesting an average of 55-58 as fairly normal

Edit: with regard to coasting, I didn't actually know that, thanks for the info! I always thought coasting was taught as economical driving because the engine wasn't needing to work and the car was effectively rolling, there's a habit I need to kick then!

 

[ajanja]

Changing your air filter and inflating tires will help you. I do exactly the same about the coasting, but I've now gaining an extra day in driving by using higher gears. Just see how dirty your air filter is, if its completely ruined then buy another

 

[britishsligean]

Make sure the car is serviced and you have a fairly new fuel filter, then try a different fuel station, go with a big brand and see how that goes, I find some places water the fuel down, especially the cheaper places, if it makes no difference maybe try some redex, they do a diesel version, I found after I used it my engine ran slightly smoother and I got a minimal fuel economy gain maybe 5 extra miles from about 10l of fuel

 

[Chino_UK]

Maybe try some fuel cleaning additive like millers eco power...I've seen good result recently on my petrol FR. You have to remember your car is 8years old now and may have gunk or other factors in it's system which inhibit max efficiency.

 

[Mk4]

Thanks for all of the suggestions. With regards to the service, it was serviced 2 months ago with a new fuel, oil, air and pollen filter as well as oil change etc, so all of that should be good.

Tyres were recently replaced on the front so maybe the garage didn't put them to the correct pressures, so I'll check that next time I'm at the garage.

Fuel wise, I am using Asda fuel so not the best. I'm curious to try out the premium fuels and measure my real world difference.

Additive wise I have had fuel injector cleaner in the last 2 tanks just in case that was the cause, but I'll see what something like Redex for diesels can do.

If I'm not down on power (or don't seem to be, havent had the car that long) is it unlikely to be anything internal that needs cleaning (MAF, EGR, Particulate filter etc.)?

 

[RyanR]

Hi there,

Pop down to ATS and get a shot of Techron-D. £20 and I swear to you it cleaned my engine right now, much better than Redex. I got excited hitting 50mpg in my 1.9 TDi and now it regularly hits 60mpg on A road driving circa 50-60 mph staying in high gear.

I know a lot of people scoff at fuel additives in general but I really do recommend the Techron, and they recommend treatment every 6 months so for £40 a year I'm not complaining, I really have noticed a huge difference, my car is an 04 so it definitely needed a good clean out and that seems to have done the job. I'm about 4 months down the line now and still getting great economy and am tempted to buy another treatment to see if it can go higher. You need at least half a tank but I recommend 3/4, it dilutes the treatment more but also means it is passing through the engine for longer, theoretically removing more gunk.

In regards to fuel I used to use supermarket but have only been using Shell/Texco fuel for a while now and it really does make a difference. I use the Premium/V Power when I can but my local doesn't stock the premium grade so I use it as and when I can but even using a proper fuel stations base fuel over supermarkets should see your MPG increasing and your engine sounding happier - I know mine certainly does!

 

[Arkaig]

Things which on separate occasions caused poor MPG on my ibiza- albeit a completely different engine: Binding handbrake (£0 and a spanner to fix - check for hot discs/drums), Faulty coolant temperature sensor (£10 - caused poor starting), and a faulty Lambda/02 sensor (£75 - Engine light came on too). Burst exhaust flexi caused a hefty dip too once.

Aircon switched on will cost you.

Is there any unnecessary weight in the car? Full size steelie spare? Roof rack?

Bear in mind that manufacturers tests will probably have been done with skinny tyres, low rolling resistance tread, premium fuel, if not other contributing factors. Saying that, the figures for the mk4's other engines seem totally achievable.

As said, coasting is not fuel efficient as the car has to inject fuel to keep the engine at idle.

The thing which had most effect on my fuel economy was getting to know the gearing. I really don't mean that in any patronising way at all, but after a while of ownership I started to experiment with just how soon I could shift up without causing the engine to labour or stall, and I soon noticed a jump from about 39mpg average to 45mpg.

And a tank or two of additive can't hurt, as an experiment if nothing else. I wouldn't go throwing lots of money at it though, FWIW 51mpg vs 55mpg over 10,000 miles of driving is about £77.

 

[Mk4]

Thanks for the suggestions. I'm actually intrigued by the Techron stuff after some googling, I might give it a shot as it looks quite effective.

In response to Arkaig, with regard to weight, no, the car is pretty much empty, normally only me in it and it's only a space saver in the boot.

As for the potential faults, would any of these throw up errors with Vagcom? Because my car comes out fine except for the well known door lock issues.

How would you go about checking the temperature of the rear brakes to check for a binding handbrake?

Edit: With regard to gearing, I am still getting used to it, but I usually change up around 2500-2800 rpm (bare in mind its a diesel) does that sound about right? I can't get 4th at 30mph like a petrol because the engine is struggling at 1600rpm

 

[vwooks]

May not appeal to you, but my average MPG went up after getting my 1.4tdi remapped.

My average is 51mpg over the 30K miles I have owned the car.

 

[Mk4]

May not appeal to you, but my average MPG went up after getting my 1.4tdi remapped.

My average is 51mpg over the 30K miles I have owned the car.

The only things putting me off the remap is this isnt likely to be a long term car, a year or two max and I'm fairly sure my insurance would take a massive hit considering im 19, in fact, they probably wouldn't insure me.

But you claim your MPG is about what im getting? Maybe I don't have any issues with my car, I was just hoping for a bit more

 

[DonCarlos]

70% motorway should see at least 55/58 mpg average, I reckon, running on correctly inflated tyres - cheaper tyres will have a lesser rolling resistance. How clean the engine oil is can affect economy quite surprisingly.

But it really does matter how these cars are driven. Changing gear as low down as possible, allowing the peak torque to do the acceleration and then immediately changing up rather then over revving the small engine is crucial for optimum fuel consumption. Steady and smooth is the way.

Some people claim they get higher mpg using none supermarket fuels - but then some others claim it makes no difference, so it's really each to their own and what suits your car.

I dunno what motorway speeds you are driving at but I believe anything over 60mph sustained speed will seriously lower the economy. Manufacturers claims are derived from ultra optimum test environments and circumstances, at a sustained speed of between 100-110 kmph, on dry, wind free days, with carefully selected tyres, on smooth test roads, without stop starting / braking, with test cars perfectly mapped and driven very smoothly.

When just pootling along at 55 mph I can get nearly 80mpg out of my 1.4tdi (Ecomotive spec 78hp) I average around 68mpg though and that's driving as I would any car getting up to 80 mph at times, mostly A & B single carriageway town and country driving. A smooth steady motorway run sitting at a steady 65mph will return nearly 90mpg.

If I drive it harder and sit at 80 mph I get significantly less. Often 15% less. And that's pretty much standard for all cars.

 

[RyanR]

Wouldn't be able to say specifically for your car on the RPM you change at but I usually change at 2K if I'm driving economically, my 1.9 TDi still pulls from near enough 1.2K just with no turbo, but doesn't stutter or anything.

I imagine the smaller engine would have to work harder to get same speeds so maybe 2.5K is about right for you but try changing sooner, and bare in mind that a diesel without the turbo active does pick up quite slowly until it's in a rev range where the turbo starts to contribute.

The way I figured mine out was just trial and error and changing as soon as possible and then seeing if the car still picked up smoothly or whether it really struggled.

EDIT: Spelling

 

[camelspyyder]

VAG's official EU figures are as good as lies in my book. The motoring media reinforce these figures by posting them in magazines and online as if they were true. Parkers just quote the claimed combined EU figure. Depending on the car you're never going to get close - especially with small petrol turbos like the VAG 1.2 tsi and Ford 1.0 ecoboost. The newer the car the more untruthful the figures are in my last 10 years experience (listed below)

2001 Proton Wira TD claimed combined 38 reality 49
2003 FIAT Panda 1.2 claimed combined 47 reality 49
2005 FIAT Multipla JTD claimed combined 44 reality 44
2014 Toledo 1.2 TSI 105 claimed combined 56 reality 45

This is a fact some motorists still need to learn - EU figures rarely translate to the real world, and some cars miss them massively - Focus 1.0/125 for instance claimed mid 60's reality mid 40's. Don't buy a car expecting the book figure, you need to budget a lot more for fuel.

On my current car:

- Aircon costs about 3 mpg
- I also have wider than standard tyres - another 3 mpg off
- The stop start doesn't always work as it should - another 6% - say 3 mpg off

It soon mounts up, low tyre pressures and poor fuel make it even worse. Our diesel FIAT ran really badly for years when SWMBO filled it at TESCO every week. I chucked a new MAF, EGR, etc. at it - cost a fortune. When she got a new job the local station sold BP - Instantly a clean running car with better mpg.

 

[Arkaig]

Our diesel FIAT ran really badly for years when SWMBO filled it at TESCO every week. .

This. After some long term testing I started to realise that every time I fill up at Tesco, the car drives like a pig and I get about 4mpg less, or about 30-40 miles less to a tank.

I thought it was in my head, but when I started getting the extra range while filling up with Shell bog standard on my daily commute, I realised something was up.

I was never one to believe in the premium / branded fuel hype to be honest, after all pretty much every bit of fuel here comes from exactly the same refinery. But somehow, Tesco fuel in particular makes my 1.4 run like crud.