Hi,

I've done just over 6000 miles in my 5 month old fabia estate 1.6 TDI (90).

Was getting between 60-70 to the gallon, then the other day worked out my consumption after a long trip and was surprised to only be in the 50's. Filled up on way down from London to Portsmouth and again surprised when the first "block" on the fuel guage went out after 68 miles - I usually expect it to go out after 90-105 miles depending on type of driving. Car seems to be running fine, no strange noises, no obvious leaks so I'm not sure what could be wrong.

Can you get a bad batch of diesel? Wouled it make that much of a difference?

Any ideas, help appreciated!

Thanks

Winter diesel is the most likely cause of your poor MPG, it has extra additives in it to prevent waxing at lower temperatures and this has a knock on effect on MPG. My superb is the same, so was my previous Octavia.

Sames happened with my Roomster Tdi, and it runs a little rougher at times too.

Also lower ambient will negatively impact things, where are you?. Other possibles - seized brake calliper, sensor fault, heavy right foot...

My economy had dropped slightly but I've put it down to 3 things

1. It's getting colder

2. I'm getting fatter

3. I keep booting it coming home from work. Can't get enough of the paddles

Time for a service?

My economy had dropped slightly but I've put it down to 3 things

1. It's getting colder

Silly question time, but how does getting colder reduce economy, I would have though the denser air would make it better :S ? I understand that additives in the winter diesel will impact but wouldn't have thought they would make such a big difference if the rating of the fuel stays the same.

Silly question time, but how does getting colder reduce economy, I would have though the denser air would make it better :S ? I understand that additives in the winter diesel will impact but wouldn't have thought they would make such a big difference if the rating of the fuel stays the same.

Longer warm up times engine spends more time on richer mixture, more load on alternator, higher air density creates more drag, cold tyres don't deform as easily increasing rolling resistance, winter fuels not as efficient, and engine, gearbox, diff and other lubricant viscosity is thicker at start of journey until warmed through.

Take your pick.

Lee

Longer warm up times engine spends more time on richer mixture, more load on alternator, higher air density creates more drag, cold tyres don't deform as easily increasing rolling resistance, winter fuels not as efficient, and engine, gearbox, diff and other lubricant viscosity is thicker at start of journey until warmed through.

Take your pick.

Lee

Thanks, still suprised at the drop he experienced as it was over a long journey so the warm up effct should be minimal. I'd get it checked out.

I reckon over long trips it should be better but round town/short trips it will drop

Thanks for all your comments.

My first time owning a diesel and had heard about the effects of "winter" diesel but wasn't expecting so much difference. And on the trip when I only got 68 miles from the first block on the fuel gauge the car was already warmed up.

Will monitor and take to garage if it continues.

Thanks Saints

Should only be a few percent, mine normally drops from mid 50s to early 50s... Not noticed anything yet, though, its not been cold enough!

This is an interesting subject and at this time of year many car owners (petrol and diesel) suddenly become concerned. Logiclee has it spot on in my opinion. Just one big factor to add...TYRE PRESSURES! Rolling resistance is increased due to temp changes, but it's also that people often don't realise how much their tyre pressures have changed from one day to the next. Example: I checked my tyres Saturday morning the other week. My Fabia estate should be 2.2bar front, 2.3 bar rear for normal driving. Actual pressure was 2.1bar front, 2.15bar rear, not a massive drop but noticeable. I would point out the pressures were correct just a few days earlier. Topped up to just over the figure for normal pressure because I suspected the following morning would be colder and thought I would allow for that. It was colder so as an experiment I checked the pressures again. All pressures were down: front 2.10, rear 2.15 again. Topped them all up again and everything is fine. Now if I had not been diligent and checked and topped up on both days my pressures would have been down by quite a bit and this would impact on my fuel consumption probably by 3-4mpg at least. AA's winter report last year said you lose something like 3% economy for every tyre that is one PSI down (can't remember the exact figure I think is was more actually). This figure grows expotentially with more loss of pressure. Factor in the very slightly lower calorific value of winter diesel and you can lose several miles per gallon. Even driving the same route into a slight headwind will of course do it even if the airflow you are driving into is not very strong. You can lose several mpg's. So with temps varying a fair bit still, check the tyres very regularly.

PS. I hope know one is daft enough to check their pressures when the tyres are warm/hot! My neighbour in his BMW 2ltr diesel was. He always stopped on the motorway services and checked them once a week. He always fixed them at the pressure in the book. I mentioned to him he should only do this when the tyres were cold, he laughed and said don't talk rubbish! So in front of him I checked his pressure cold and found they were down by 8 psi on what they should be. He was shocked, I topped them up for him, and he now gets 6-8mpg more and the car handles properly like it's never handled before he said! It just illustrates how important pressures are to modern cars if you want to achieve or get near to manufacturers fuel economy figures.

Edited 7 November, 201114 yr by Estate Man

Sounds like you are like me and can tell when the tyre pressure is wrong, even by only a few degrees... The car just doesn't seem to handle as well with wrong pressures in, even though I don't flog it I tend to corner quicker than many people and its there that i notice it...

Mind you when i raced a car we always used to check the pressures right after the race ready for the next one!!

I do need a tyre pump at home since pressures should only really be done from cold. Can anyone recommend me one? Did have a cheap one from Tess Co but it burnt itself out the fisrt time I used it.

You are ok if the local garage is only a mile or two from home, it shouldn't have warmed up too much by then... Best bet is to get a separate tyre pressure gauge, I wouldn't rely on the ones on the pump (either yours or the garage's!), they never seem to be accurate on the ones I've used...

I have a Machine Mart JS1010 Jump Start. It's a combined jump starter, work light, 12V power supply and air compressor.

http://www.machinemart.co.uk/shop/product/details/clarke-jumpstart-1010?da=1&TC=SRC-jump start

Saves the bother of having to run cables out for pumping up tyres. The pressure gauge is rather crude but I double check with a Michelin Digital tyre pressure guage.

http://www.amazon.co.uk/dp/B000V5F0XQ/ref=asc_df_B000V5F0XQ5127274?smid=A3P5ROKL5A1OLE&tag=googlecouk06-21&linkCode=asn&creative=22206&creativeASIN=B000V5F0XQ

Cheers

Lee

I have a tyre pumpy thing from Halfords, It cost me £11.99. It's a stirrup pump for bikes actually without a gauge on it (long upright thing hand operated with a place to put your feet on it each side to secure it when pumping). It has a high capacity for pumping tyres on cars or motorcycles or bikes. I use a separate tyre gauge. I got fed up with the foot pumps on sale everywhere, they don't last five minutes. This Halfords one is good and is very very strong. Had it a year now and use it on my car and motorcycles.

Mine looks like this but without the gauge.

Tyre pump

Edited 7 November, 201114 yr by Estate Man

There's even a chart in the manual showing economy reduce with ambient temperature. Effect of the seasons can clearly be seen in my fuelly long-term chart - that car does exactly the same journey every day all year round. Previous year was the same and note I don't change tyres.

Not only is running MPG lower but the DPF regenerates more often too.

Edited 7 November, 201114 yr by pearce_jj

pearce, that's interesting about the DPF regens occurring more often. I suppose it's mainly down to everything running at lower temps and perhaps the bigger amount of fuel being dumped into the engine for longer after startup. That too is going to knock the mpg's a bit.

How do you know when regen is occuring?

No way to tell on VW's unless you turn the engine off during a regen cycle then you get both cooling fans running for around 10 minutes after switch off and a nice smell of something very hot.

First time it did it I had residue burning off the heatshield on a brand new car and I thought it would burst into flames.

Cheers

Lee

First time it did it I had residue burning off the heatshield on a brand new car and I thought it would burst into flames.

Cheers

Lee

+1 (Gave me quite a fright).

How do you know when regen is occuring?

Easy to tell in the Fiat 500 as the engine gets even more grumbly than usual, idle speed increases to 1,000 rpm and trip MPG dives.

Don't know about VAG diesels as I've not driven one with a DPF. There are a number of different methods I think; never noticed it in Citroen 1.6 HDi for example.

Edited 8 November, 201114 yr by pearce_jj

How do you know when regen is occuring?

No way to tell on VW's unless you turn the engine off during a regen cycle then you get both cooling fans running for around 10 minutes after switch off and a nice smell of something very hot.

First time it did it I had residue burning off the heatshield on a brand new car and I thought it would burst into flames.

Cheers

Lee

On mine tickover is just under 1000rpm during active regen cycle rather than the normal just under 800rpm when stationary and 900rpm when in neutral / clutch disengaged but car moving.

Some say they notice engine running differently but I can't discern any change.

How do you know when regen is occuring?

No way to tell on VW's unless you turn the engine off during a regen cycle then you get both cooling fans running for around 10 minutes after switch off and a nice smell of something very hot.

First time it did it I had residue burning off the heatshield on a brand new car and I thought it would burst into flames.

Cheers

Lee

On the GL1 power decreases a tiny bit. You also get a very obvious increase in exhaust note. It sounds a little bit like a very mildly blowing exhaust for 5 minutes then its done, most noticeable around 2000 rpm. No smells and no fuss.