Why suddenly started using more fuel?

[tomas_v]

2011 Audi A4 B8 2.0TDI (88kw)
I was really happy with fuel economy. On average it was 6 l/100km (thats about 40mpg) and its mostly city driving. But now it jumped to average of 9 l/100km (26mpg).
What could be causing it? Nothing serious was done to the car.
Only oil was changed (filled with Neste longlife). And oil, air, saloon and, I think, fuel filter were changed? (4 filter in total that's for sure).
At first I thought they overfilled oil, and other garage confirmed there was a bit too much (I drove about 1000km before they refilled). But still its using too much fuel.
Especially when driving slowly, or starting to move. I have never seen 40 l/100km before, but now every time I start driving it jumps up to 40l/100km (5.88mpg). And I can see it is higher on same roads as before. When cruising on highway I get about 5 l/100km (47mpg) and that's more less ok.
Can any of those filters cause this? Can it be something with suspension? Brakes, though they do not heat up? On my other Audi that I had before dirt got in to calipers and cylinders weren't moving properly. But then disk were heating up extremely.
I am taking my car to a dealer for a service so I will point this out to them, but still would like to have some other opinions.
Thank you

[theskyfox]

Hi,

Couple of thoughts.....

-How are you calculating your fuel economy? Are you looking at your receipts and the miles you have done, or are you using the Driver Information System display figure? The DIS figure is known to be inaccurate and really is just a rough guideline.

-What fuel do you use? e.g. supermarket, BP, ESSO. The miles per litre of fuel can vary depending on the quality and cetane level.

The way I calculate my fuel consumption is like this.

1. Fill the car up until it will not fill any more at the pump, Set the trip computer to 0.0 miles.
2. Drive the car normally for a few days.
3. Fill the car up again until it will not fill any more at the pump, and keep the receipt.
4. Take the number off the trip computer - e.g. "100.5 miles". Take the number of litres you put in the car off the receipt.

Finally..you will then know the real consumpton of the car. E.g. 100.5 miles = 30 litres. Based upon this, you can then work out the miles per gallon....so in this example, 30 litres = 6.59 gallons which = 15.25 Miles per gallon.

Hope that helps.

-Andrew

[tomas_v]

Ye, I am using just On board computer. I do understand its is not the most precise tool for that, but i was using it before and now. So it should be the same.
I live in Norway, I fill up in ESSO or Shell, Statoil. Would think it is good quality fuel. And I was filling up at the same gas stations before the increase.

Yea, I filled up like you did, will check the results later.

[magt1000]

Use Fuelly to keep a proper track of your fuel economy (see my sig)

[tomas_v]

Thanks will check it out.

But if I am right and mpg went down? Could any of above cause it (filters, oil) Or should i be looking at other problems?

[Doctle Odd]

You need to ignore the minute by minute fuel consumption data. Were the filters you fitted genuine? 1000 km is a long drive with too much oil IMO. I suggest you get a diagnostic scan and post the results on this forum

[tomas_v]

It wasn't me personally that changed oil and filters. But that garage is quite good, doubt they would use cheapest ones.
They filled up 4,5 liters of oil. They checked car specs for that. And at dealership, they said it was just slightly more than it should be. So I hope no damage was done.
But can incorrect oil level damage engine that much? Can it be the reason why it is using more fuel?

[Doctle Odd]

If it was only a little over it shouldn't make any difference. Get the scan done it could be unrelated to the work you had done.

[JimC64]

presumably its not the difference betwen summer and winter driving?
That will account for a few mpg's varation for sure!

[tomas_v]

No. its same summer driving.
Will ask them to do the scan.