Measuring fuel usage by Weight.

Hi Craig

If your happy with 20lt increments and taking an estimate of whats left you certainly can get an estimate.

This process though is far more accurate and allows you to pick up trends far earlier.

But then sometimes its better to tell the story of how big the fish is rather that be dissapointed by weighting it.

I imagine Robin was concerned re: Evaporation ect.

Hi Daza

I should have added that an entires days driving might only consume 15 - 20lt of fuel and an estimation from this small amount can lead to large percentage errors.

Sorry Robin, have to agree with Craig here, now you are being pedantic. Surely you don't need to know to the 500ml. If thats the case then you are not carrying enough in my opinion. Trips away should be as casual and fun as possible, weighing fuel I draw the line at..! LOL

Hi Terra

Weighting the fuel gives same result as using a fuel guage , but then I have known some that don't look at those either and have run out.

But as you say maybe "you are not carrying enough" - this is the whole point, with this method there is less guesswork about knowing that you are indeed carrying enough.

I disagree Robin sorry, whilst I understand what you are trying to achieve, carrying fuel to the "ML" is a recipe for disaster. I always carry extra to allow for emergencies. I know you are a perfectionist and I admire that, but just saying I am happy to carry 20-30 litres extra. I have never mis calculated my fuel useage and most of my trips are to the middle of Bass Strait where you can't buy fuel.

I understand what you are saying also Terra and of course nearly always it doesn't count - but it changes when you run into other issues like effectively carrying and managing over 300lt into unknown situations .

We were actually safter because we didn't need to carry fuel to the last "ML" because we could measure things and hence forward plan !

This actually happened on our trip -> we pulled up at a stop and someone said oops whats this - oh oh my jerry can has leaked , I don't know how much I have left.

Guess what the answer to this situation was !

Is this a case of wanting to know too much information that you don't need to know.

All we want to know when remote traveling is what is going to be our worst fuel usage and then carry enough fuel plus a bit to cover the distance we need to travel.

Didn't know the Madagan Line was part of the "world fuel economy test".

Trying to calculate fuel to be taken to the last liter is asking for problems.... don't think road side assist covers the Madigan.

That's why our 200 series has 330lts of diesel storage on board with another 80 avalible if needed.

When we did the Madigan and the Hay River we calculated on using 30Lts per 100 and lucky we did... from the Hay River Track / Madigan Line turn off to nearly Bookies camp we were in low range 2nd gear all the way battling strong tail winds making vehicles run hotter then normal.

By the way Robin was the Partol over weight?

Hi Richard - Sounds like someone on my trip that wouldn't go to a doctor because he might not get the results he wanted.

One of the beauties of taking the time to get it right as that you don't need to take excess fuel , as such our car completed our trip and weighed in under GVM at 2900kg all up about 400kg at least lighter than some others.

The same technique was also used on water - and in the end we completed this difficult trip with remarkably little fuel for a 4.8lt petrol car.

This lower weight also contributed to us being the only car not requiring any assistance.

Maybe driving style has a lot to do with not getting stuck, we got stuck on one sand dune and the only reason we got stuck was I wasn't paying attention and went a bit to slow with the long range belly tank bottoming out on a peak, a extremely light very low speed snatch by a friend in his Disco of no more than 3 feet was needed..... it wasn't really a snatch more like a tug.

I should of been away doing the Madigan and Plenty Lakes at the moment lokking for the famous "Friedrich Wilhelm Ludwig Leichhardt" remains but still prepping the 200...... to add salt to the wounds we were lying in bed last Sunday morning listening to Macca on the famed radio show "Australia all over" and one of our friends on the trip phoned in from camp 6... not happy Jan!

If you want to have a listen to the phone call go here -

http://www.abc.net.au/australiaallover/listen.htm

And got to the 'LISTEN TO LAST WEEKS SHOW" and click on the 7.00am to 8.00am AEST cast and go to the the 31 minute mark.

Always next year when we go back up.

Its so beautiful out there at the moment Olcoolone - lets hope next year only takes 6 monhs to come

Hi Robin

Just looking at some statistics

15 replies, 54 follow-ups, would this be a record on this Forum, if no, what has been the biggest number of replies to a question? And what question generated so much interest?

Nah, there have been much bigger over the years, but I can't remember what they were.

Peter

Hi Al

You can't use this method for whats in the main tank of course , but the majority of the fuel wasn't in the main tank , and in Patrols you can even dump your subtank back into the main tank.

So by the time you are into your main tank you have used some 200lt and have a very good idea of your usage.

In our case we used less fuel than expected and actually began the last days travel with a full main but empty sub.


Seperate from the above you can get a pretty good idea of main tank usage when the needle is right on a line like a half way mark , in my own case I have also developed a little computer module which linearizes the fuel guage and
provides not only better readings but calculates the slosh factor which generally relates to rougher conditions and can be used to predict forward your range.

Hi Robin,

In my case all the fuel is in the tanks to a total of 270 litres so I am reliant on the gauges. By observing the gauge during tank filling and noting the servo pump readout I have a reasonable correlation of dash gauge to actual litres.

If I wanted more accurate measurement of consumption I would consider fitting a fuel flow sensor and readout.

However, I question the value of more precision when the variation in terrain has such a significant effect on fuel consumption. Precise measurement seems somewhat academic to me.

I'd love to have 270lt fuel tanks Al.

My weight measurement approach is only relevant to those who need to carry jerries etc.

Yes Robin, I'm looking forward to the next trip in a few weeks time.
The Troopy had 2x 90 litre tanks and I was pushing my luck some times so I have just replaced the rear tank with a LongRanger 180 litre to give the 270 litre total.
Any jerries would have to go up on the roof-rack but I would not be happy about that.

Even when the full 270 litres is not needed I now have the benefit of purchasing fuel at better prices than at some of the remote settlements at high prices.

The OEM tanks had a reasonable correlation to the dash gauges but I have yet to determine the situation with the new LongRanger. So far I have only been able to establish that from full-tank to where the gauge begins to move down from its top stop is about 10 litres. Of course I am more interested in the relationship at the bottom end and hoped to run it to empty before leaving home but 180 lt takes a bit of using up with domestic driving and I cannot find enough containers to drain it.

Having an instrumentation background I had thought about fuel metering (as I do with the batteries) but with no ECU and mechanical diesel injection it would need two fuel flow transmitters plus the appropriate processor and readout. I appreciate the relative simplicity of my Troopy (no ECU etc) and would not want to compromise its reliability with flow meters in the fuel lines. If I could utilise the signal from electronic injectors I may be tempted however. Gotta do something between trips after all! lol

I would offer a couple of suggestions Al

To improve my fuel tank reading I took out the fuel sender and lowered it so that it reads the important part , the bottom and it misses a bit at the top as a result.

Rather than flow meters it can be done by simply linearizing the existiing fuel guage.

This requires a compliant wife to fill your main tank 2lt at a time from a jug while you do the arduous task of writing down the voltage reading.

The readout becomes more complex , I designed a special mirco circuit for this but for occasional use this can be a simple as reading a voltage off a plot chart.


Have a great trip.

Robin, when the tank was being fitted I requested that they ensured that the gauge read correctly with the tank empty and to not worry about the full tank reading. They assured me that was their usual method and from the 10 litre over the gauge 100% it may seem that is the case. My problem is to get the fuel tank empty to see the bottom reading. If I can I will adjust the float arm to read 0%.

The gauge was reasonably linear in the old tank so should be also in the new one but it is a bit higher which may account for the extra 10 litres above the gauge 100%.

My wife is pretty compliant but 180 litres at 2 litres at a time? Your'e joking!
No, if I can get it empty she can read the gauge whilst I call the fill from the servo pump. But although I could, I would not be fitting a compensating module to the gauge. It surely could not be that bad!

Hi Landy

It actually makes things a lot simpler - you simply fill up the tank and note the fuel weight - quite easy with this device.

An alternative might be that you fill up your tank with say 3/4 of a jerry and guess that its 3/4 - with this there is no guessing.

It also allows you to use multiple fuel containers of different sizes because the weight measurement doesn't require a container of a special size or shape.

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Seperately as per response 2 above I have already developed a point of no return fuel use calculation micro which does not require the extra cost of a fuel flow sensor. (uses only guage(s))

A side benefit of the above is that I can enter a number relating to the fuel remaining in containers and have it added to the fuel tanks value and hence compute an even better figure.

Hi Robin

I hear what you are saying, but unless you can pinpoint the actual flow from the tank usage is going to be varied due to the fact that you won’t have a constant power setting on the engine. This being the case weighing the fuel versus an eye-ball of (roughly) 3/4s of a jerry can probably isn’t going to make that great a difference, you might be a couple of litres out, but unless you are measuring fuel flow to the engine your calculation of fuel usage will be out in any case.

It is worth noting that the specific gravity of fuel is not precise either, but usually an ‘average’ value is given. The density of diesel is in the range of 800 to 950 kg per cubic metre, with an average of around 880 kg per cubic metre. This works out to a specific gravity of 0.7635, but you appear to be using 0.7250, which highlights potential variances that can occur through a weight measure.

Mind you, I’m not suggesting we all run out and buy a fuel flow meter at $1,000 a pop, but equally I think it becomes almost academic the impact of either measuring fuel by weight or volume and simply adds another step to filling up the tank.

And don’t get me wrong here, whatever works well for you is best for you, but I can’t reconcile that by adding this step you are going to get any greater degree of accuracy then if you don’t.

Cheers,

Hi Landy

Flow meters are essentially instantenous devices as is power flow at any time.
Any long term measurements rely on multiple readings which simply build errors.

What you really need to know is the likely range over the terrain you are covering.

So by getting an accurate usage figure at the end of each day you are better equipped to predict forward , this type of measurement effectively smoothes out the entire days running with its varying power flows etc.

Its also independant of specific gravity and can cover all fuels provided you do what I do (write down fill amount and weight when you fill).

Its really good because I can use unleaded 98 95 or 91 from different suppliers as well as any old container size.

Espically useful when you find out the kids have sneaked a couple of liters out of your jerry !

Like anything , better information leads to better results.

Hi Robin

Fuel flow meters are just that, they measure first and foremost the actual fuel supplied to the engine, and therefore provide a very accurate reading on fuel burn. All other calculations it makes are derived from this. “Long term measurement does not rely on multiple readings that compound into errors”.

But I did qualify, in my first response, that the use of a fuel flow meter in a vehicle to get a snapshot at any given point of time on ‘fuel flow rate’ will be difficult because power settings in a vehicle are not constant. And you are correct to say that simply relying on a ‘fuel flow rate’ reading at any point of time is not helpful for forecasting range.

However, it still measures quite accurately actual fuel supplied to the engine (actual fuel used) and therefore at any point of time you (or the device) can calculate actual fuel used for the distance travelled; the average burn rate. It does not rely on multiple readings to calculate actual fuel used. So no need to wait until the end of the day to calculate the fuel you have used, it is available to you at any point of time. Besides, the calculation you make at the end of the day is still an ‘average burn rate’ whether you measure into the tank by volume or weight.

I flew many aircraft with fuel flow meters, and most were usually linked to NMEA output, so a range and fuel usage to destination could automatically be calculated. Because aircraft are generally flown at a constant power setting you can simply glance at the fuel flow per hour to gain an insight to ‘fuel burn’. But another way of doing it was to simply take the actual fuel used to any point of time, and compare it against the distance travelled to calculate the ‘average’ burn rate per kilometre. You could do the same in a vehicle at any point of time quite accurately.

I’m sure there will be many EO members who have used similar in either larger motor boats, or possibly aircraft. But again, I don’t suggest we all spend $1,000 on having our vehicles fitted with them as for most it would be an over kill. But for regular, long-range remote desert travellers it may well be a great investment and viewed as a safety aid...

The discussion on fuel flow meters is an aside to your original proposition. And as I qualified earlier, whatever works well for you is best for you. However, I can’t accept that by determining fuel usage via a weight calculation improves the process of determining fuel usage any more so than by measuring by the volume you are adding, which I think is the point you are endeavouring to make.

“Long term measurement does not rely on multiple readings that compound into errors”

Hi Landy - We have a clear discussion point if you believe this.

A fuel flow meter only works by its controller reading out values at specific intervals e.g. 1 per second.

The multiple readings go into its controllers data queue and are rounded off - usually to a fairly high accuracy though.

Whenever a derived calculation is required it is further processed.

Along the way comes an additional error source -temperature , the material expands and different volumes are required for the same reading. In aircraft grade products this error is indeed small , but typical products like devices for
private cars have much larger errors.

On top of this are both pressure related errors and density related errors.

There are several electronic articles on the construction of fuel flow meters for cars and the general conclusion is that accuracy is not high.
So much so that it is considered better to measure the injector pulse width
and duty cycle and as fuel pressure is regulated , to derive a fuel use measurement.

Compare this to a single weight measurement which relies only on the accuracy of the measuring device.

My key point is really that a simple $20 device can quickly make a practical measurement - whereas to measure the liquid volume of odd containers is just not practical and even less practical if in plastic containers whose volumne varies with temperature.

Whilst you might be able to weigh your jerry cans to get a calculation of how many litres are left in them, or how much you placed in the car’s tanks, it is only part of the equation. Your theory is flawed because you are unable to measure the weight of the fuel in the car’s fuel tanks, well at least I’m assuming you can’t. Therefore you can’t determine how many litres are left in the tank, surely an important consideration.

If you could do this then we would have a clear discussion point...

If you are concerned about getting the exact amount of fuel remaining in a jerry can, save yourself the hassle of lifting, weighing and making a conversion calculation. You simply take a wooden broom-handle, start with an empty jerry can, and measure off one litre increments into the jerry and mark a graduated scale on the broom-stick handle, works a treat...

But, in the meantime, I’ll accept the perceived error rate in the fuel flow device over a subjective weight measure, undertaken on a $20 dollar device, held up by someone in the middle of the desert, that only takes account of part of the equation...

And yes, you mentioned a system you have come up with of measuring flow and enabling a PNR calculation, but let’s face it, it is more likely to be prone to error than a commercially available fuel flow device, and if it isn’t, and is more accurate, give up your day job and sell the idea to the car companies, you’re set to make a motza!

I’m not mocking you or your idea, I just can’t see the point of it...

Landy , I think you may have missed a step in the process.
There is no need to know the weight of the fuel in you tank, we all know how much our tank holds.

The process was to fill your tank from containers , and measure how much it took.
Then you can make accurate use calcs and determine the point of no return etc - once you only have the main tank left then you can use whatever means you would normally use be it fuel guage etc
In my senario most of the fuel is held outside the main tank


So simple and cheap to add this extra capability , espically when you can even use it to weigh your fish catch as well.

I’m having a Bex and a lie down...

But before I do, I don’t think I’ve missed anything. Measuring fuel into the tank, by any method whatsoever, weight, litres, or a combination of both is fine, you can establish how much fuel has gone into the tank with some degree of accuracy either way. I think we can both agree on that at least.

But at this point how do you know how much is in the tank unless you measured how much left the tank and was consumed by the engine. If you are concerned about the accuracy of a properly calibrated fuel flow meter it is unlikely you are going to have any more faith in a standard vehicle’s fuel gauge telling you the tank is full even if it is a Nissan. And if you can establish within 10-15 litre accuracy it is probably okay, providing you are building in some kind of ‘reserve’ buffer, the margin for error, when you have done your fuel planning..

But, at this point, I’ll take you back to your original post in which you’ve suggested measuring the fuel by weight is more accurate way than doing so by volume. That is the notion I reject simply on the basis that for what you are trying to achieve there are other factors that will make differences between weighing the fuel, and measuring by volume so small it is pointless and only adds an additional step...

And caveat has been, what works best for you...is best for you, and I’ll rest at that, the Bex is kicking in...

Cheers...

Hi Landy

Stuff the Bex , I'm home with a chardonay.

In my senario the fuel tank is a constant not a variable - one simply fills the tank till it overflows (almost).

Now the real question - Will you still loan me that book !

Hi Garry

I think you have actually stated the problem - you don't know that you have used 20lt - unless you monitored how much you put into in the first place them and probably need to label them as well (most 20lt can hold up to 23lt).

You then have to empty one fully to know you used 20lt if you recorded it, and then remember if any was part used , leaked or evaporated.

All thats pretty hard and then you need to consider the case of odd sized containers and what if the main tank didn't fill with exactly your 20lt , which is almost always the case - it just becomes to hard - whereas a simple $20 device can do a much better job.

Hi Captain

I have such devices and a scanguage is a very useful tool but not for this situation.

It has absolutely no knowledge of how much fuel you have left in your containers.


On other uses yes there are many , we carry water in 10lt casks , and its so easy to measure how much you have left , the other day I had another cute use.

Someone was telling me this tyre was good it had so much rubber - quite some surprise when I wihipped out this little guage , weighed the tyre and asked some highly relevant questions about the manufacturers data sheet !

Worth the cash just for the looks I got !

Hi Robin,

I agree that knowing exactly what you have put in the tank is good, but once in the tank you currently have no way of knowing how much you are using. So for the final ~125L in the tank, its now based on the GU tank guage and I know how accurtae that is!

As you say, and we all know, the fuel use changes considerably depending on the terrain. So when you have emptied all your accurateky measured containers and only have a "full" tank left, its an unknown quantity of what you actually have left in the tank as you draw it down!

The scangguage is as accurate as 0.1L per tank, you just need to calibrate it - not that difficult at all. Any error based on summing discrete flow data is minimal and I am more than happy to know within 100mls what I have in my tank :)

And yes, the little weigh devices certainly are useful. Mine more than paid for itself when I was able to distribute our luggage in 11 suitcases when we returned from the USA. Even thought I thought I had packed them evenly, it was suprising the difference between the small and large cases and what my "calibrated" arm said were the same 23kg weight :)

Cheers

Captain

I have a ECU talk and you can reset the fuel meters so when you fill up both tanks add the volume of the Jerry's and will quickly know how you are travelling. I am guessing the scangauge does the same thing.

As someone else has mentioned ‘a solution’ in search of a problem....

Start of trip measure total litres of fuel into all storage devices used (fuel tanks + jerry cans). Once you have done this it doesn’t matter how much you have left in the jerry cans, you are working on total fuel held, regardless of where it is held.


In a nutshell the equation goes something like this.

Step one: (Fuel tank fuel + jerry can fuel) = total fuel carried

Step two: (Total fuel carried – actual fuel used measured by scanguage or fuel flow meter) = total fuel remaining

Step three: (Total kilometres travelled / actual fuel used) = average kilometres per litre burned

Step four: (Total fuel remaining * average klms per litre) = Estimated range to fuel exhaustion

Not sure what I am missing, but I can’t see that ‘weighing’ anything helps any more, or less. And as I said previously, the only way you can get an accurate read on usage is to measure the fuel supplied to the engine.

Hi Troll

Have an ECU talk here also , but its not as much use in the situation I proposed and certianly more complex, it also requires someone to have a such a device
and most do not.

,
Pretty hard to beat a $19.95 device which has all the other side benefits mentioned above.


In practise all I need to do is grab the little device and directly read out the weight of which each .725 kg is a litre , don't even have to switch on the ignition.

Then I can go and help measure other peoples fuel use - Oops , maybe thats a disadvantage.

Each to their own I guess Robin, but I think you are overcomplicating things just a tad :)

"Pretty hard to beat a $19.95 device which has all the other side benefits mentioned above."

Bit of dowel rod as a dipstick works well for me in jerry cans and other containers.

Bob

But does it do this Bob - Can you measure my petrol jerry and then someone elses diesel jerry - mind you some believe a bit of petrol in the fuel does wonders for the tractors.

Turn the stick upside down.
Do that with your scales :-)

Bob

You win Bob - but my wife can't stand the smell of fuel on the fingertips.

Nearly didn't find this AL, I was looking up higher - No those jerries were needed to come up with 300lt total which includes 175 in the Patrols 2 main tanks.

My containers actually all took different amounts from 5.5lt to 24lt and this is where the scales really shone, its so easy to measure weight a few days after filling when you forget - it interesting that there have been so many replies to this thread , when the weight method is probably the only way you can measure fuel post a fillup.

The most important thing on a trip like ours when we actually did drive 6 days into a huge obstackle , is to know when is the turn around point and the escape options.

Its not ideal of course but the drive in gives you a good feel for a possible drive out , and in the face of unknowns its probably the best you can hope for.

300 minus 110 equals 290 ????
I can't do math either!!!

Thats another benefit of weighing Brian - but I'm having trouble convincing some of even the more basic points .

So how often do you send the scales off to a NATA Laboratory for certification? If this is not done then your scales could be 10% or more out. Comparing them to another set or an amount/weight you reckon is correct is also frought with errors.
Cant believe I have actually replied to this nonsensical thread.

The concept of weighing fuel is pretty simple and practical Bigfish.

But you raise a good, if nerdy point as does Brian above - these things require appropriate levels of accuracy, not Nata level, and this item has been checked against secondary standards in a professional engineering lab, even in a temp controlled facility.

You'd probably be amazed at how many of the cheap electronic devices like voltmeter sold to unsuspecting buyers just don't stack up.

Strewth Brianc...seemingly many of us are struggling with the act of measuring the amount of fuel added to a car from a jerry can, and you are throwing into the mix the complexities and impact of environmental factors on managing the in-flight fuel usage of an aircraft. ;)

I need another Bex!

Landy, have you got a spare Bex there mate?

Ive been reading this chuckling away-until I got to the bit where the $19.95 scales have been tested in a temperature controlled lab.

I have to say Robin, if youd bought a turbo diesel your fuel usage would have been a little more than half, and you wouldnt be in this strife of struggling to make your fuel last.

I think we are being wound up here and how many of us have been hooked.....

" I think we are being wound up here and how many of us have been hooked....."

Never fisho64 - I'm just filling in till friday funnies start then I'm off to the bush again.

And there I was, woke up today thinking it was Saturday, as I was sure this was the Friday Funnies thread I was knocking around in yesterday ;)

Cheers,

My mate Galileo was the only person who didn't think the earth was flat Terra - I think he still may be.

No Muntoo, the weight of the fuel does not change with temperature, only the volume changes.

Better information always makes for better decisions DD , and refining your data along the way is often the difference between making it and not.

I have been on trips with some who have turned around and later found out it wasn't necessary.

In 2 hours I'll be on the tracks again , so keep'em in line till I get back.

I as a very limited experirence on all things 4x4, woke this morning at 6 am, with a &*^%$#@ hangover. Made a coffee and switch onto E O. Read a few threads and bumped into this one. I have tried to understand what it is all about and now at 8 am I am no wiser than I was at 6 am. But gentlemen, I think I have sobered up a bit and found it to have been one of the most entertaining morning in the last few months. Can anyone explain to me the relevance of wieghing the 4 lt Cask at the beginging of the evening and then prio rto turning in. After trying to force a dip stick into it or getting the other half to measure each glass during time spent drinking, to achieve the best nights sleep in the shed. Help from the wellinformed/sober forumites could contribute to my problem. Now where is that Sheeeeerr Razzzzz.

Must sober up for the trip to Silverton

Touche' dude, however must say that is one hell of a way to attempt identifying the 'turning back' point, especially when you have absolutely no idea what is ahead of you. For example - nice and dry, flat, obstacle free terrain or the 'obstacle ridden course from hell.

I totally agree however that you must constantly keep an idea on fuel usage, especially in the initial stages of the trip to ensure that your vehicle is performing as anticipated and the, if necessary, reassess the situation and make a timely decision re same

You have a good time on the tracks this weekend and I'll most probably see you at this years Pyrenee's gathering if get there.

DD

And the Madigan Moose is one such place as it is far more difficult to head West meaning the turnaround point is not halfway. This year the unknown distance to detour the flooded Eyre Creek also meant while it's great to know exactly how much fuel you have, there is no accurate way of telling how far that would get you over unfamiliar terrain nor how often you'd waste fuel getting bogged & the subsequent recoveries.
I'd suggest the ISP for Robin on this past trip may have been quite close should there have been a touch more water barring progress to the East. Once you commit to heading south from the Madigan it's a long way back to Mt Dare or up to Jervois when carrying a conservitive amount of fuel.
Putting the weighing fuel theory aside this has been an interesting discussion on the many considerations for fuel use in remote areas which rarely get touched on.
Cheers Craig..............

Hi Crackles

Your very last point is spot on!

Ralph, have you taken into account the temperature coefficient of expansion of the particular wood of the stick? Allowing also of course for the expansion of the fuel. Oh, and for the container.

Aaaargh..it's all too hard. I might just carry a bit of extra fuel!

Now that's lateral thinking Ralph.