136 diesel mpg drop from 62 to 52 over 8000 miles

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136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Crunchynut » Fri Jan 06, 2017 7:32 pm

I've beven using my 136 diesel over roughly the same weekly mix of driving since new (daily commute plus the odd weekend run about).

When new, the computer said I was getting 62mpg ( though my calculations suggested a real mpg of 56) per tank. This has steadily reduced over the 8000 miles covered so far, so now the computer is reading 52mpg per tank ( I reset it each fill up).

Has anybody else seen this kind of trend?

Any thoughts on a cause?
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby mattonecz » Fri Jan 06, 2017 7:38 pm

winter and winter tires maybe? oil degradation aswell.
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Crunchynut » Fri Jan 06, 2017 8:32 pm

No change in tyres, and the drop off started way before the cold weather.

Oil deg ... could be. I hadn't thought of that. Could it have that much effect ?
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby JJ-Yorks » Fri Jan 06, 2017 9:45 pm

Doubt it is down to the oil quality as my economy went down by around 4mpg in November so I got the oil changed even though it was only changed in May and it made no difference...but I had decided as mine is the 3 cylinder turbo I would change the oil twice a year.
I would put it down to the fact the temperature has dropped as in the summer I did 65 mpg on a good run and on a recent similar run over Christmas I averaged 57mpg
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Crunchynut » Fri Jan 06, 2017 10:39 pm

I agree the cold weather will make a difference, but I got the car in June and by early October (no appreciable change in temperature) it had dropped from 62 to 54, month by month.

I wondered whether injectors may be clogging. Shouldn't do at this mileage, and I usually use Esso rather than a supermarket fuel, so should be half decent in terms of additives.
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Crunchynut » Fri Jan 06, 2017 10:59 pm

JJ-Yorks wrote:I would put it down to the fact the temperature has dropped as in the summer I did 65 mpg on a good run and on a recent similar run over Christmas I averaged 57mpg



On a long run, the poor economy of the cold engine when setting off is soon dwarfed by the economy of the many miles being covered. Once the engine is hot, you should get better economy on a long run on a cold day because the air is more dense. Tyres migt be a bit softer mind.
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Anupanu » Sat Jan 07, 2017 12:43 am

Even subconsciously would you have 'run the car in' to start with? Also you don't say whether your calculations back up the loss of mpg. Could it be the computer?
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby mattonecz » Sat Jan 07, 2017 11:04 am

Crunchynut wrote:No change in tyres, and the drop off started way before the cold weather.

Oil deg ... could be. I hadn't thought of that. Could it have that much effect ?

idk in our old octavia 2 1.9tdi new oil, (Mobil 1) helped, but we had really old and bad oil in it after we bought it 2nd hand
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby Crunchynut » Sat Jan 07, 2017 11:18 am

Anupanu wrote:Even subconsciously would you have 'run the car in' to start with? Also you don't say whether your calculations back up the loss of mpg. Could it be the computer?



Reduction in computer read outs is matched by manual calcs. Computer now says 52 and manual calc gives 47.
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Re: 136 diesel mpg drop from 62 to 52 over 8000 miles

Postby phead » Wed Jan 11, 2017 7:35 am

Can the readout be totally trusted?

I'm getting 53 with the same engine, the same at I did with the GTC, but I'm putting less fuel in, so one of them must have been wrong.
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