Waht can cause a sudden drop in miles per gallon?

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Sure AC means lower mpg, but you can't have your cake & eat it too.
On our A3, if I put it in 'economy' mode, a message comes up telling me that if I continue to use the A/C, I will be burning 1/8th of a gallon of fuel per hour. Big deal!
 
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On our A3, if I put it in 'economy' mode, a message comes up telling me that if I continue to use the A/C, I will be burning 1/8th of a gallon of fuel per hour. Big deal!

Does it actually say 'gallon' as opposed to litres.
I'm an old fart who doesn't accept change easily, but tend to calculate consumption in miles-per-litre as pumps have delivered fuel in those units for decades.
In the case of my cars anything over 5 miles per litre gets the (y)
 
A Little update. I took the car out 7.30 this morning and had a 20 mile run. its getting about 50 percent MPGs I would expect. I noticed when I put it in neutral or take my foot off the accelerator the speed drops more than you'd expect. I'm no expert but Im suspecting the brakes. Theres no pulling to one side, maybe a little screach once or twice when I wasnt braking but nothing conclusive.
Think it's got to go to the garage. :(
By the way this post isnt me complaining about getting less value for money on fuel its my suspicion that something is wrong with the car.
And the aircon is off.
 
A Little update. I took the car out 7.30 this morning and had a 20 mile run. its getting about 50 percent MPGs I would expect. I noticed when I put it in neutral or take my foot off the accelerator the speed drops more than you'd expect. I'm no expert but Im suspecting the brakes. Theres no pulling to one side, maybe a little screach once or twice when I wasnt braking but nothing conclusive.
Think it's got to go to the garage. :(
By the way this post isnt me complaining about getting less value for money on fuel its my suspicion that something is wrong with the car.
And the aircon is off.
go and feel each wheel after you have just stopped, is one of them hot ?
does your car freewheel on a slight slope ?
 
How many miles on the diesel?

Could be due to hot weather,

But could also be partially blocked intake manifold, diesels like to coke up the insides, seen many a PSA/ford 1.6 & 1.4 hdi do this.

Other makes don't also though

I had the intake flap stuck open about 10 months ago. P2015 fault code I think. The repair was more than the cars worth. In the end I found a bracket on amazon which stops it going open too far. That flap open meant the car could run lean I think. If its blocked as you say it would run rich and mean less MPGs. So that is a possibility. I hope its not that.
 
Its done 160,000 miles. Ill try feeling the tyre heat also.

It did freewhell down hill but bot as fast as I expect.
 
Some car owners are obsessed with fuel consumption figures.
To be fair, if they do a lot of miles, and are concerned about expense and/or emissions, its a reasonable "obsession".


My only income is a pension, but I still enjoy the comfort of older petrol driven cars that were executive transport in their day.
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If you suspect a braking problem, simply jack up each wheel in turn and verify it spins easily. Try it both before and after brakes are applied, including the handbrake. I suggest that a 50% reduction in fuel economy would create mucho heat if it were the brakes, and a smell to go with it.
 
If you suspect a braking problem, simply jack up each wheel in turn and verify it spins easily. Try it both before and after brakes are applied, including the handbrake. I suggest that a 50% reduction in fuel economy would create mucho heat if it were the brakes, and a smell to go with it.

Thats it! The front nearside one is pretty tight. Not sure what that means or what to do but it's a start.
 
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