Sudden Increase In Fuel Consumption

[bucketmaster]

Drove to France yesterday (diesel Octavia Estate 4x4) and during the first hour or so of the journey the MPGs settled at the high 40's. Suddenly I noticed it dropping for a while until it finally settled at around 35/36. I was driving fairly fast, fully laden with a large roof box but it should be a lot better than that. As soon as I accelerate significantly or hit the slightest incline the MPGs drop right down to around 20, which it never did before. There is no discernible difference in the way it drives, not that I've noticed anyway. If it was the MAF sensor wouldn't there be a big drop in power? I guess also a dragging brake could be the culprit. Is there anything I should look out for?

Edited 2 November, 2014 by bucketmaster

[FLAPPERJACK7]

Lol

[silver1011]

4x4, full boot, roof box, motorway speeds = significantly increased fuel consumption.

 

When you say that it never used to be as bad, are you comparing a similar previous journey (i.e. with the roof box etc.)?

 

A lot of the petrol stations are now making the move over to winter diesel too (additional protection against waxing in low temperatures) which will also have a negative affect on fuel consumption.

 

Also, don't believe the onboard computer for instant or average MPG. The only way for a fair or accurate reading is by doing a manual calculation on a full to empty tank.

[bucketmaster]

I see what you mean. But with the aforementioned I was getting mpg in high 40's then all of a sudden - no change in temperature/driving style/fuel etc and around 15 mpg reduction.

 

To make sure I wasn't being paranoid took it for a test drive minus the load on some quiet country roads and was getting max 40mpg instead of the usual 55+.

 

It's definitely not right.

[silver1011]

Touch the brake discs after a journey to see if one is hotter than the others.

 

Have you checked the tyre pressures recently?

[bucketmaster]

The tyre pressures are fine. Will check the brakes out.

[Guest]

You will know if the brakes are binding if the car resists rolling on a very slight gradient, it doesn't take much for a car to roll, try taking your foot off brakes at traffic lights and you'll see the car roll to the lowest point on the road surface.

Badly performing brakes can also be felt as a tail dragging sensation, nose diving sensation and/or a combination of those and a brake bias to one corner at very slow speeds as in queuing traffic.

If in doubt, get out and try pushing it on level ground, it should roll easily once you get going.

If you're really keen jack each corner up in turn and give the wheel a spin by hand.

Re winter diesel, I've noticed my displayed average drop 5-10mpg in the last month using Scottish diesel.

[DanialA11]

Re winter diesel, I've noticed my displayed average drop 5-10mpg in the last month using Scottish diesel.

Yep same here I thought it may have had something to do with a pothole that took my tracking off but looks like I'm. Not the only one

[Aspman]

With all that on the roof it could be something as simple as a change in the wind direction. Wind behind you to wind in front of you could easily knock 10mpg off the car.

 

If you're checking the brakes do it from cold and only drive for a short distance. Brake disks get very very hot. Imagine checking if an iron was on by putting your fingers on the plate. I learned that the sore way ;-)

 

Check your oil, my VRS used to use more petrol as the oil level dipped.

 

Check your tyres a slow puncture might cause drag

[mixskoda]

I noticed on my Octavia that when i was coasting to a halt you could feel the brakes bind just as it stopped. When i got home i felt the brake discs and the right rear was warmer than the left, also there was more brake dust on that wheel. When i jacked it up you could feel the binding when trying to spin the wheel. I ended up taking the wheel off and stripping / cleaning the pads, carrier and caliper and wound the piston back in, put it all back together and its fine now, for now.....

[Guest]

@mixskoda

Good work and fingers crossed but you've probably just bought some time before it happens again, I usually find that taking the piston and seals out and cleaning everything up is the only sure way to ensure trouble free operation.

[Peter.C]

Drove to France yesterday (diesel Octavia Estate 4x4) and during the first hour or so of the journey the MPGs settled at the high 40's. Suddenly I noticed it dropping for a while until it finally settled at around 35/36. I was driving fairly fast, fully laden with a large roof box but it should be a lot better than that. As soon as I accelerate significantly or hit the slightest incline the MPGs drop right down to around 20, which it never did before. There is no discernible difference in the way it drives, not that I've noticed anyway. If it was the MAF sensor wouldn't there be a big drop in power? I guess also a dragging brake could be the culprit. Is there anything I should look out for?

 

Since late October I've noticed exactly the same thing with my diesel 2.0 Octavia Estate. I do 500+ miles a week, so I keep a close eye on fuel consumption. A couple of hundred miles into a tank there was a sudden drop of 10-15% in economy. Like you said, it mainly seems to be under acceleration that it's much poorer. I consistently get 57-60 mpg average from a tank (calculated, not taken from the computer, though I find it's only about 2% difference), but that week it went down to 52 mpg with no change in type of journies or driving style. I almost always use Sainsbury's City Diesel (most convenient, and cheapest). I filled up with a tank of Shell V-Power, which helped to take it back to close-to-normal, so perhaps there has been a change in the fuel properties to "winter" diesel which is affecting it. Local Shell station is being re-furbed, so as soon as it's open again I'll try normal Shell diesel to see how that performs - can't afford the extra 10p a litre to keep using V-Power diesel!

[gregoir]

Since late October I've noticed exactly the same thing with my diesel 2.0 Octavia Estate. I do 500+ miles a week, so I keep a close eye on fuel consumption. A couple of hundred miles into a tank there was a sudden drop of 10-15% in economy. Like you said, it mainly seems to be under acceleration that it's much poorer. I consistently get 57-60 mpg average from a tank (calculated, not taken from the computer, though I find it's only about 2% difference), but that week it went down to 52 mpg with no change in type of journies or driving style. I almost always use Sainsbury's City Diesel (most convenient, and cheapest). I filled up with a tank of Shell V-Power, which helped to take it back to close-to-normal, so perhaps there has been a change in the fuel properties to "winter" diesel which is affecting it. Local Shell station is being re-furbed, so as soon as it's open again I'll try normal Shell diesel to see how that performs - can't afford the extra 10p a litre to keep using V-Power diesel!

I've had my car for 70k or so. I manage to get up to 51mpg- same journeys. Calculated always- which inevitably agrees with the computer (sorry to upset you).

Drops to ~47mpg  on winter fuel if I do not drive cautiously or when I had sticking brakes this year. Never managed to better the mpg either on motorway ( genuine70mph cruise all the way to Dundee) or a cross country 50/60mph trundle to Norfolk..

Rarely used supermarket fuels in UK. Total or Esso.

[bucketmaster]

Think I was just being a complete spanner but it turns out there was a loose section of exhaust which may or may not be related?

 

It's all good now.

[trundlenut]

I had a boost leak caused by a split in the hose which comes out of the turbo and joins to the hard pipe going to the intercooler. It made a difference to fuel consumption then it properly split and kept dropping into limp mode. It also caused a hesitation at low revs though.

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