Ibiza fuel economy dropping

[Mike C]

Hi, I would be very grateful for any advice please.
I have a 2018 Ibiza 1.6tdi FR, 20k on the clock. I do about 400 miles a week, mainly on dual carriageway, for approx 30 mins a journey. I bought the car specifically for the fuel economy which was advertised as 74mpg. When I got it in June I was getting 66mpg, which I could live with (real world conditions etc). But since then it has been dropping and I'm now struggling to get 54mpg. It's killing me on the fuel costs.
I've taken it to the dealership and they have run a diagnostic, which didn't return any errors.
Car has had major service in the last month, tyre pressures checked, and driving with a very light foot.
Not really sure where to turn next.

 

[RUM4MO]

Low winter temperatures will have an influence of MPG when compared MPG during summer running temperatures.

 

[Mike C]

Thanks for the reply Rum4mo, and yes, I agree, it will make a difference being colder...but, this started happening before it got cold. From what I've read it could be a number of things...dpf, oxygen sensor, air filter. I guess the first two would trigger an error on diagnostic, and was thinking of changing the air filter for a relatively cheap option, which I could then rule out.

 

[SRGTD]

Interesting news article from last year at the link below on the impact of cold winter weather on using E10 petrol, one of the impacts being much worse fuel consumption compared to E5 petrol;

E10 fuel and winter weather combine to drop fuel efficiency

A COMBINATION of freezing temperatures and the new E10 fuel is seeing drivers filling up more often.

www.express.co.uk

 

[Mike Coulter]

It’s winter mix diesel. I found this with my VW Golf GTD too.

 

[Mike C]

It’s winter mix diesel. I found this with my VW Golf GTD too.

Thanks Mike, but we started getting this issue before it got cold...in September it started dropping. Was wondering whether a new air filter and an economy remap might be the way to go...

 

[Mike C]

Interesting news article from last year at the link below on the impact of cold winter weather on using E10 petrol, one of the impacts being much worse fuel consumption compared to E5 petrol;

E10 fuel and winter weather combine to drop fuel efficiency

A COMBINATION of freezing temperatures and the new E10 fuel is seeing drivers filling up more often.

www.express.co.uk

Thanks SRGTD...ours is Diesel, but as Mike below has mentioned diesel also has a winter mix...

 

[Mike Coulter]

Thanks Mike, but we started getting this issue before it got cold...in September it started dropping. Was wondering whether a new air filter and an economy remap might be the way to go...

I’d look it up, they may actually start changing the mix around then.

 

[SRGTD]

Thanks SRGTD...ours is Diesel, but as Mike below has mentioned diesel also has a winter mix...

Oops! Apologies - missed that vital piece of information in your first post .

When I had a mk6 Golf GTD, the fuel consumption did suffer during the winter months - from memory it was around 10% worse during the winter. I put it down to the car taking longer to get up to optimum operating temperature and the winter blend of diesel fuel.

Traditionally, I think filling stations switch to winter blend diesel fuel from around the middle of November to mid March.

 

[Mike C]

Oops! Apologies - missed that vital piece of information in your first post .

When I had a mk6 Golf GTD, the fuel consumption did suffer during the winter months - from memory it was around 10% worse during the winter. I put it down to the car taking longer to get up to optimum operating temperature and the winter blend of diesel fuel.

Traditionally, I think filling stations switch to winter blend diesel fuel from around the middle of November to mid March.

Haha, no worries. Appreciate your reply, and I've learnt something new...wasn't aware of winter fuel mixes!
However, our issue started in September, and has been falling since. We're down 30% against advertised, and have lost almost 20% from when we first got the car.
Which is why I feel like there must be something wrong to cause that.

 

[KXL]

From a non Seat car, but from an Audi A3 1.0TSI MHEV, in summers a said journey of almost 100 miles mainly on motorway going 70mph, gave me 60mpg. I just did the same journey in winter last weekend, it was raining, but not particularly cold (9 degrees), and it returned only 54mpg. 6mpg short.
When it was -2 couple of weeks back, short journies was only in the mid 30s mpg, regular winters at least 40mpg plus. Now I can't comment on when the fuel mix changes, plus mine is petrol, but maybe the diesel shortages has something to do with it?
Back in the day when I had a Leon 2.0TDI, usually fueled with Shell/Esso/Texaco, eg proper fuel stations, then one day decided to put £20 worth of supermarket diesel in (the dealer told me to NOT do this unless in emergencies) and viola, readout showed 5 mpg poorer over the journey where as the 100 other 'same' journies prior I made would have mpg within 2mpg of each other, the one with the supermarket diesel was 5mpg down! Engine noticeably grumblier too!