To all you wonderful gurus out there. Okay have a 2010/11 F2 SD4, 174000 kilometers on the clock. When I first got it it would do 6.5/6.9 Lt to the 100 kilometers this has now crept up over the past 2 yrs to 8.8/8.9. so about 25mpg. I generally use it to drive into town a distance of 15 kilometers average speed 80kph. I have a gap tool and had a look at a few specs today, so boost absolute pressure 1.4v, 801rpm, exhaust gas temp bank 1 4.9v fuel rail pressure 50750.0 kpa, intake air temp.3.0c, mass air flow 12.9 g/s. The thing I have no idea what to look for to see what needs to be check, cleaned, replace or what lvls anything should be to be able to get the fuel consumption improved. So any info on what to look for or anything that has been done to rectify reduced mpg gratefully received. Have started to use clean diesel over the past few months as opposed to the tree juice we normally get palmed off with here in Sweden but this hasn't made a difference yet. Ideas As a secondary note she runs as sweet as can be, regular serviced at around every 15000 km.

30% drop in economy is quite a change.

Just a thought, but have you serviced the Haldex? If it is like the F1 VCU, degrading of it would put stress in the transmission that would consume fuel. Doubt that would account for a 30% drop though - I'd have though summat would have broke first if it was that bad!

I am not a FL2 driver and might be mistaken, but would have thought that 8.8l/100km would be roughly 32mpg's?
That doesn't change of course the issue, but other might be obetter on the fl2.

tyres and pressure all good - have you added anything to the car ti add weight or bodywork, wind deflectors etc - The MPG in my daily would regularly drop in winter time

6.5-6.9l/100km is around the 40mpg mark

How do you measure fuel consumption? Per tank full?
You'll use a bit more fuel when it's cold, but not that much.
Have you checked for a fuel leak?

When you say, regularly serviced, is this done by yourself or a garage? In the UK, most garages can't be trusted to do a proper service. What type of oil is being used and has the air filter been changed recently for a decent one? Also what type of tyres are you using and what are the pressures?

Col

On a motorway in summer mine will achive about 40mpg but local in the winter only about 24mpg. I thought it was the repeated cleaning cycle of the dpf?

okay will try to answer all comments , which by the way are gratefully received. Oil change in vcu but didn't do the filter, will do that asap, also done a change of oil in the diff which looked okay. It is -5c at the moment and don't have a garage to do it in at the moment because of covid restrictions (I normally use a friends garage with lift). Used a online converter to do the maths (not my strongest point) on the fuel conversion it could have converted to usa gallons thus the discrepancy. so yes it is 32mpg which isn't so bad but still not the best. 6.9 lt/100k yep been stung by the police here with speed cameras and it gets expensive 200 quid a pop so in my old age have toned down the right foot a bit. Tyre pressure is the recommended 2.2bar. no extra added weight. Using the vehicle's gauge to monitor average litres per kilometre, resetting when filling tank. Yes it can get cold, really cold sometimes, -35 for a week or so in Jan/feb but this is not just a cold weather thing. No leaks of fuel, Service done by myself in my friends garage with him looking over my shoulder Normally do a complete service oil, filters, etc, Oil is the recommended Castrol Edge for the motor.
So my thoughts were on stuff like was the turbo wearing, things gunging up etc. Hence the request for figures on maf or boost so I had a base line toward from. I don't want to dive in pulling stuff off the vehicle and fixing stuff that doesn't need fixing. And as previously state thanks for the comments.

Stv123 said:

On a motorway in summer mine will achive about 40mpg but local in the winter only about 24mpg. I thought it was the repeated cleaning cycle of the dpf?

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yep got to look into seeing how I can force a dpf clean with the gap tool. I believe it can be done just not sure how.

I would fill the tank, do a mix of driving until the reserve light comes on then fill up, at the same fuel pump if possible, then you know exactly how many km you have done and how many litres used

Snaggapuss said:

Using the vehicle's gauge to monitor average litres per kilometre, resetting when filling tank.

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That's not accurate, as it only gives the fuel fuel usage for the last 50km.

kermit_rr said:

I would fill the tank, do a mix of driving until the reserve light comes on then fill up, at the same fuel pump if possible, then you know exactly how many km you have done and how many litres used

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This is the best way.

kermit_rr said:

I would fill the tank, do a mix of driving until the reserve light comes on then fill up, at the same fuel pump if possible, then you know exactly how many km you have done and how many litres used

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okay will give that a go and see what happens but with covid restrictions that might take a while :-(

I always reset the trip when the light comes on and put 30 liters in, then i can gauge if it goes up or down.
I got a carbon clean on my high miles A6 3.0 V6 diesel - it done the business - increased performance and fuel economy, but - my friend also got it done at the same time, same machine - he didn't notice much but his was a low miles 1.9 audi, and i now have to do injector seals. still worth it I think.