Fuel consumption...

This is a serious question...don't laugh

Ok, where has all my diesel gone?!

I had a full tank and my red light is on and about half way down the red area, I have done 235 miles, it usually does at least 300, the first 1/2 of the tank seemed to last quite well, but in the past few days it has shot down really quickly and I have hardly done any mileage nor have I been really hammering it at all, in fact less.

Could I have a small fuel leak...I don't see how as I haven't been offroad for a while, thre isn't any fuel on the floor underneath, I don't think, what could it be?

I did have my fuel thingy tweaked but I haven't been using the extra power at all. I really don't understand how it has gone down so quickly all of a sudden! Help!!

Oh, and its a 200 TDI 90

You'd struggle to see a leak because the fuel will evaporate, or is this just petrol? The only thing I can think of is that it's due to your pump being tweaked. Or is it the late night trips to dominos!?

no, I haven't done hardly any driving, but I normally get around 300 if not more to the tank. But I haven't been using the extra power so it shouldn't affect the fuel consumption, its only if you put your foot down more.

its bugging me so much!!!

hmm I know it's not the same thing but since I redid the induction system on my car my mileage has gone down from 65 to about 53mpg when I drive sensibly. are you getting any black smoke at all?

how many litres is the defender tank. im doing about 460-480 on a full tank in my disco. 88 litres

Hmm, im not sure how many litres in my tank! but to a tank its usually 300, and im on 235 with just a bit more left to go til off the red and empty!

I don't think I am getting any black smoke! soo annoying/confusing.

haven't got your handbrake on?

got any extra weight in there?

OK.
heffs - diesel is an OIL, and so it dnt evaporate
letsgoagain1 - if you have had the pump tweaked, thats where your fuel has gone.
It will have altered not just how much fuel is delivered, but how it is delivered, so yes it will use more fuel.
If you put a 3 litre engine into a micra, and drove it at the same speed as a 1 litre micra, what will use more fuel? Even though you aint using the power, it still gets burned.

Your turbo boost pressure will also have been upped, so you won't see any black smoke, even though there is more fuel being pushed in.

My 90 has a 55 litre tank - to the red bit does around 250 miles - my first tankful outta the 300TDI did this, but i have been driving it fairly, umm, enthusiastically.

Oh yeah - open the bonnet, and check all the pipes for leaks. My NA lost me 5 mpg cos i had slight misting of fuel on the lift pump pipe. It was damp, not dripping at all.

Sure it hasn't been siphoned off?

technically diesel fuel is a hydrocarbon, the same as gasoline, so chemically have similar properties, I wasn't sure if the longer HC molecule chains caused it to not evaporate at ambient temps. so there. I don't think she had the turbo upped, just the pump tweaked, by torchlight, in a pub car park

Some people eh

boydy1989 said:

OK.
heffs - diesel is an OIL, and so it dnt evaporate
letsgoagain1 - if you have had the pump tweaked, thats where your fuel has gone.
It will have altered not just how much fuel is delivered, but how it is delivered, so yes it will use more fuel.
If you put a 3 litre engine into a micra, and drove it at the same speed as a 1 litre micra, what will use more fuel? Even though you aint using the power, it still gets burned.

Your turbo boost pressure will also have been upped, so you won't see any black smoke, even though there is more fuel being pushed in.

My 90 has a 55 litre tank - to the red bit does around 250 miles - my first tankful outta the 300TDI did this, but i have been driving it fairly, umm, enthusiastically.

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oh crap, I was told it should use no more fuel or less. So I have simply been using more fuel!? So I should un-tweak it so that I am not going to be 100% poor and cry.

Do you reckon mine has a 55 litre tank too, that sounds about right, since I had a full tank it done 235 to the half way down the red which is ****!

Any other options?! And thanks for you reply!!

TheVengefulElephant said:

technically diesel fuel is a hydrocarbon, the same as gasoline, so chemically have similar properties, I wasn't sure if the longer HC molecule chains caused it to not evaporate at ambient temps. so there. I don't think she had the turbo upped, just the pump tweaked, by torchlight, in a pub car park

Some people eh

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haha, yeah only the pump wotsit not the turbo,

If you're not using the extra power available isn't it worth turning the fuel pressure back down anyway? If doris is quick enough then you don't need it and you can eliminate it as a cause!

TheVengefulElephant said:

If you're not using the extra power available isn't it worth turning the fuel pressure back down anyway? If doris is quick enough then you don't need it and you can eliminate it as a cause!

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yeah, well I liked having it there for ovetaking, but I didn't hammer is cos I had the extra power because I knew it'd use more fuel, I just thought it'd not use fuel so long as I wasn't putting my foot down more.

So maybe I will get it turned back when this individual is back from holiday next week. And see if it goes back to normal.

Thing is, the 1st 1/2 lasted very well but from between 1/2 and 1/4 it has just disappeared like crazy. its slightly odd

letsgoagain1 said:

yeah, well I liked having it there for ovetaking, but I didn't hammer is cos I had the extra power because I knew it'd use more fuel, I just thought it'd not use fuel so long as I wasn't putting my foot down more.

So maybe I will get it turned back when this individual is back from holiday next week. And see if it goes back to normal.

Thing is, the 1st 1/2 lasted very well but from between 1/2 and 1/4 it has just disappeared like crazy. its slightly odd

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Didn't you say before that you don't normally pay much attention to how much fuel you're using? because fuel gauges are renowned for being inaccurate, the first half of the gauge in my car actually equates to nearly two thirds of my tank, so it looks like the second half goes down really quick!

TheVengefulElephant said:

technically diesel fuel is a hydrocarbon, the same as gasoline, so chemically have similar properties, I wasn't sure if the longer HC molecule chains caused it to not evaporate at ambient temps. so there. I don't think she had the turbo upped, just the pump tweaked, by torchlight, in a pub car park

Some people eh

Click to expand...

In a pub car park... And your asking why your fuel consumption has all gone wrong... Honestly... I was expecting a proper job!

Yes diesel is *just* a hydrocarbon, its also *just* a liquid. The longer HC mollecule chain is what determines most of its properties, like its ignition temperature, volatility, density, viscosity, etc. Why do you think that veg oil, another *just* hydrocarbon burns differently again? And how do they get different *just* petrols to give different amounts of power?

Yeah! I did physics A Level too!

I know what your saying, but petrol is a spirit and diesel is an oil, which is why a basic petrol engine will run on ethanol, and a basic doosel will run on veg oil, but not the other way round.

And to be really technical, diesel (and other oils) do evaporate. But... It takes a veerryy long time. And now, for a copy and paste job cos im bored of typing, heres HOW the longer HC mollecule make it dry slower.

"When a liquid evaporates, its molecules must separate themselves from their attachment with
others in the liquid and then move off into the air space above. Heating the liquid makes the
molecules move faster and weakens their attachment to each other. That is why warm liquids may
evaporate more quickly than if they were cold.

Nevertheless, the molecules in some kinds of liquids, like oil for example, are rather large and
well-tangled up and attached to each other. This means that evaporation, if it occurs at all, is
very slow. That is why cooking oil, even though sometimes heated to a very high temperature,
does not evaporate to an appreciable extent."

Oh, im not being snotty, i just didn't include enough of these in the last post.

And my first half of the fuel gauge goes down much slower than the 2nd to, its a LR trick you see.

yer not wrong. looks like there's more than one pedant afoot here then boydy

boydy1989 said:

its a LR trick you see.

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Say that in a welsh accent and it fits purrfeck

Yer've been in bangor too long boydy! ooh me mate goes to bangor uni

TheVengefulElephant said:

Didn't you say before that you don't normally pay much attention to how much fuel you're using? because fuel gauges are renowned for being inaccurate, the first half of the gauge in my car actually equates to nearly two thirds of my tank, so it looks like the second half goes down really quick!

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I do pay attention! well, maybe it has all of a sudden become inaccurate but it has always been pretty reliable I thought, maybe I will check underneath some how to see if there is a leak, but it scares me going underneath, maybe I am claustraphobic.

Its crap, I will have to see if he can change it back, well he can, but I don't know why so much more fuel has gone, as it should use the same or less if I am not putting my foot down, I have hardly done alot of mileage for the amount of fuel that is gone, im very aggravated now!