Odd fuel consumption??

I've been working out my fuel consumption for a few weeks and The results are a bit puzzling. The vehicle is a 110 hardtop with a 2.5td and no mods that might effect fuel consumption except for some fat bfg muds. Been running on 100% pump diesel. Worked it out on two fill with normal driving, no attempt to economise, pretty much flat out acceleration and cruising at 65mph ish, got an average of 27 mpg. Then had a go to see how economical I could be, short shifting, trying to stay off the gas as much as poss, and cruising at a max of 55 mph, only managed 24mpg. It don't make sense
Anyway I'm back on 50/50 veg oil mix now so going to do a similar test and see if there's any difference.

Changing up early is not always the most efficient way of doing things as if you are in too high a gear the engine will be working harder and this will counteract any advantage of being in a high gear. If you sit down with the torque & power curves for your engine, together with the gear ratios, you should be able to get an idea of the theoretical best change up points. I would imagine that changing up so early it drops off the turbo will not help at all.

Davec said:

If you sit down with the torque & power curves for your engine, together with the gear ratios, you should be able to get an idea of the theoretical best change up points.

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I know long winter nights is commin but FFS!

I meant to add that for an accurate figure you need to do it over more than one tankful. I have kept a record of every drop of fuel that has gone in my motor over the last 3 1/2 years, generally pretty consistant but every now and then I will get an rogue figure, usually cancelled out with the next tankful, so probably an air lock causing the pump to shut off early.

mondo said:

I know long winter nights is commin but FFS!

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I quite agree, I may keep a record of all fuel used, but I'm not that sad.


However if you know the mph per 1000 rpm, in the book somewhere, and the gear ratios, it should take long to calculate the rpm per 1000 in each gear, then multiply by the revs for peak torque (also in the book) and that should give a good guide.

With most Landy Diesels, even the TD5, running steadily at about 2,000 rpm seems to give good economy.

CharlesY

Know what you mean Davec. No revcounter so I was trying to keep it in the band where I can hear the turbo whistling. It does drop the revs a bit too much when I change up I think which could explain it I suppose.

my 110 as is does about 330 miles on a tank - bung a set of ladders on the roof and somehow I get 350... guess they're just fickle? Makes absolutely no sense though.

muddythelandy said:

my 110 as is does about 330 miles on a tank - bung a set of ladders on the roof and somehow I get 350... guess they're just fickle? Makes absolutely no sense though.

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Mine had a bloody great roof rack on when I got it. Took it off and put 10mph on the top speed

CharlesY said:

With most Landy Diesels, even the TD5, running steadily at about 2,000 rpm seems to give good economy.

CharlesY

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And peak torque on a Td5 occurs at











































1950 rpm

Sadly I ain't got one of them new fangled revcounter things