Is there something wrong I’ve gotten great mpg?

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ben 300tdi 90

ben 300tdi 90

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44
Location
Northamptonshire
Hello
I’m the owner of a defender 90 300tdi with 262,000 miles. Today I decided that I would see what mpg I get I did 121 miles 60% country roads 30% dual carriageway or motorway and the final 10% in town I used just 14 litres of fuel giving me an MPG of 37. It was the first time I had worked it out as usually I do a green lane which would screw with the results. It’s not down on power or anything and I don’t drive it hard I’m wondering if anything is wrong or should I just enjoy it. I will add photos to prove it.
 

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My 90 with a 200 Tdi get mid thirties to the gallon so it is doable. The 90 is lighter than a disco so if driven sensibly, it does return respectable figures.
 
Keep the weight and speed down with roadish tyres pumped up to proper pressure along with a light foot and not to much in the way of hills the quite possible.
There was this fella who's neighbour had a VW beetle and was always going on about how good the MPG was. So the fella decided to have some fun and every night over the next few weeks nipped over the fence and added increasing amounts of petrol to the beetle's tank. The neighbour was overjoyed boasting how the more he drove the better the VW's got delivering 150 mpg! He then started taking fuel out and of course the mileage crashed. It drove the neighbour nuts endlessly servicing his car trying to regain the lost mpg
 
I have worked out the MPG on my 90 300TDi every time I fill up for the past 20-years and I have never recorded a figure as good as that although I am not saying that it is not possible, the only way to be sure is to work it out on a regular basis to ensure no rogue data has been used.
All my calculations are done by brimming the tank and then dividing the fuel used into the mileage.
General running around will record a figure of between 26-30MPG whereas a long motorway journey will record 32-33MPG. Since converting to auto back in 2016 the general figure has dropped to 24-25MPG but the motorway figure has remained the same (which is understandable).
These are not one-off figures but calculated using the same method of collecting data over a period of 20-years so give a reliable indication.
 
my 200tdi gets me 35mpg when it's empty. I did record 38mpg once. Towing however, brings it down to low 20's, but saying that it was 3t horse trailer with 2 strapping horses, up long steep hills in the depth of Wales that hammer the engine.
 
tottot said:
Keep the weight and speed down with roadish tyres pumped up to proper pressure along with a light foot and not to much in the way of hills the quite possible.
There was this fella who's neighbour had a VW beetle and was always going on about how good the MPG was. So the fella decided to have some fun and every night over the next few weeks nipped over the fence and added increasing amounts of petrol to the beetle's tank. The neighbour was overjoyed boasting how the more he drove the better the VW's got delivering 150 mpg! He then started taking fuel out and of course the mileage crashed. It drove the neighbour nuts endlessly servicing his car trying to regain the lost mpg
Click to expand...
Yep I certainly don’t drive fast I do use BFG AT KO 1s at 30 psi
 
ben 300tdi 90 said:
I wonder if it may have something to do with the gear ratios. I’m not sure but the previous owner said that it had RRC differentials in the axels I wonder if the 2.5na (I’m assuming that was what was in it before the 200 tdi) had lower diff ratios
Click to expand...
I have a disco rear axle and the 1.4 transfer box. It may be the tyres or it needs the pump checking. I don't accelerate aggressively and I stick at around 55mph. With the 10 gallon tank I barely make 280 miles from full. Tomorrow I am picking up another tank and I will fit it under the passenger side after moving the battery box. It beats carrying a bunch of Jerry cans!!
 
Diffs are the same.

There are two things you need to know when calculating MPG, the exact mileage covered and amount of fuel used.
For mileage you have to be certain that the speedo is reading correctly, if the tyre size has been changed but the speedo drive-gear has not then the mileage will be incorrect. Have you checked the speedo reading against a GPS or the mileage against known distances?
For fuel used you cannot use the gauge, it has to be done by brimming the tank and then filling to the same point when you re-fil. One-off readings are not a reliable indication, the more times you do this the more accurate the calculation and you can see the difference in journey type (motorway, urban, twisty B-roads etc) and driving style (hard acceleration or steady throttle).
 
Litch said:
Diffs are the same.

There are two things you need to know when calculating MPG, the exact mileage covered and amount of fuel used.
For mileage you have to be certain that the speedo is reading correctly, if the tyre size has been changed but the speedo drive-gear has not then the mileage will be incorrect. Have you checked the speedo reading against a GPS or the mileage against known distances?
For fuel used you cannot use the gauge, it has to be done by brimming the tank and then filling to the same point when you re-fil. One-off readings are not a reliable indication, the more times you do this the more accurate the calculation and you can see the difference in journey type (motorway, urban, twisty B-roads etc) and driving style (hard acceleration or steady throttle).
Click to expand...
I don't know about the OP but I have checked mine over the last 1000 miles so only 4 fills. It has returned the same every time. Miles and speed based on GPS data and paper maps. Surprisingly the speedo is quite accurate though.
 
Litch said:
Diffs are the same.

There are two things you need to know when calculating MPG, the exact mileage covered and amount of fuel used.
For mileage you have to be certain that the speedo is reading correctly, if the tyre size has been changed but the speedo drive-gear has not then the mileage will be incorrect. Have you checked the speedo reading against a GPS or the mileage against known distances?
For fuel used you cannot use the gauge, it has to be done by brimming the tank and then filling to the same point when you re-fil. One-off readings are not a reliable indication, the more times you do this the more accurate the calculation and you can see the difference in journey type (motorway, urban, twisty B-roads etc) and driving style (hard acceleration or steady throttle).
Click to expand...
Yep I do do it by Briming the tank because the guage is bad and the speedo does read 5mph fast so maybe that has slightly inflated the mileage
 
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