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I've done nearly 6000 miles in my Logan Diesel and have noticed that, for pretty much the same driving conditions, distance travelled and even very close mpg readouts, the 3rd time I fill up is about 25% lower mpg than the previous two!

I use the same diesel pump at a slow fill rate to the first click, filling from about half a tank (or at least on the read out). It is usually 27 liters (tank is 55) but the third tank is between 33 and 38 liters for the same 360ish miles! I would get around mid 60's 1st and second fill, which is pretty much what the readout says. Then the third tank it would read out mid 60's again but it has been as low as 45! The average of the 3 is still over 56 so I'm not complaining just wanted to know what is going on!

I know that DPF regneration occurs at some point and when it does 8 times more fuel is injected into the cylinders for about 10 minutes or so. BUT, nearly 10 liters more to do this sounds insane as that is the equivalent of 4.5mpg AT 70MPH or a drained tank in less than 50 miles!

The pump seems fine I filled up a 6 litre can and it was spot on. I doubt someone is syphoning it as it is every 3rd tank and pinching as little as 6 liters from between 25 and 55 in a tank is daft!

Any ideas?

Thanks,

Charles
 

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I've done nearly 6000 miles in my Logan Diesel and have noticed that, for pretty much the same driving conditions, distance travelled and even very close mpg readouts, the 3rd time I fill up is about 25% lower mpg than the previous two!

I use the same diesel pump at a slow fill rate to the first click, filling from about half a tank (or at least on the read out). It is usually 27 liters (tank is 55) but the third tank is between 33 and 38 liters for the same 360ish miles! I would get around mid 60's 1st and second fill, which is pretty much what the readout says. The the third tank it would read out mid 60's again but it has been as low as 45! The average of the 3 is still over 56 so I'm not complaining just wanted to know what is going on!

I know that DPF regneration occurs at some point and when it does 8 times more fuel is injected into the cylinders for about 10 minutes or so, but nearly 10 liters more to do this sounds insane!

The pump seems fine I filled up a 6 litre can and it was spot on. I doubt someone is syphoning it as it is every 3rd tank and pinching 6 liters from between 25 and 55 in a tank is daft!

Any ideas?

Thanks,

Charles
Hmmm the person pinching your fuel only has a 6Ltr can lol...
other than that perhaps you are not filling it up at exactly the same half a tank point, once the half a tank light comes on you can drive quite a few miles before it drops down another bar.
You say you fill to the first click diesel foams when filling the tank, to different degrees depending on atmospheric conditions / temperature.
Fuel also expands in warmer conditions, and contracts in colder conditions so you will use more fuel in colder conditions...
Always fill your tank when its cold outside... For instance if you fill up first thing in the morning when its cooler ( contracted fuel) rather than in the afternoon when its warmer (expanded fuel) you will get slightly more for your money.

Lastly rather than attempting to gauge your fuel economy by the half tank, Try doing it by the full tank and see if the results are any better.. Remember to fill up fist thing in the morning or when its the coldest point of the day.. My Favourite time is around 6 in the morning after the night temp.
 

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Hmmm the person pinching your fuel only has a 6Ltr can lol...
other than that perhaps you are not filling it up at exactly the same half a tank point, once the half a tank light comes on you can drive quite a few miles before it drops down another bar.
You say you fill to the first click diesel foams when filling the tank, to different degrees depending on atmospheric conditions / temperature.
Fuel also expands in warmer conditions, and contracts in colder conditions so you will use more fuel in colder conditions...
Always fill your tank when its cold outside... For instance if you fill up first thing in the morning when its cooler ( contracted fuel) rather than in the afternoon when its warmer (expanded fuel) you will get slightly more for your money.

Lastly rather than attempting to gauge your fuel economy by the half tank, Try doing it by the full tank and see if the results are any better.. Remember to fill up fist thing in the morning or when its the coldest point of the day.. My Favourite time is around 6 in the morning after the night temp.
Seems one has to average over the tanks - just filled up again without using Eco Mode and many short trips (computer 55.8mpg average) to see if that had a difference. I did 371 miles and the tank just turned 5/8 fuel. I used 24.46 litres so 9 litres less to go 11 miles more in all city traffic. So I guess fuel isn't lost it's just what you said really!
 
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