A different slant on the thread below
I am surprised that with modern tecnology we cannot have accurate fuel guages. I have driven a number of cars with computers that purport to show the range left but I have no confidence in them.
On a Primera it would sometimes drop from an indicated 50 miles range remaining, to show 0 miles remaining, inside 10 miles. As an experiment(with a full can in the boot) I once drove 40 miles with it telling me I was out of fuel before I chickened out and filled up.
The older Beetles were best. You could look into the fuel tank and see the bottom of it. You could also drive until it spluttered and then turn the reserve tap on(situated inside the car) and you had exactly 5 litres left.
Has anyone experience of a really accurate system?
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Whlst we have the (archaic?) system of a float being being the sender, readings at both top at bottom ("full" and "empty") cannot be accurate.
My experience with modern cars showing "estimated range left" has been that they are much more use than a needle showing "about a quarter" left.
Even if you may be in for some "interesting" readings.
My wife's Skoda Fabia Tdi regularly shows more miles left after driving 20 miles! Obviously, this is because the initial "guess" is a simple calculation, adjustments take into account driving style, greater than average use of 5th gear, etc. etc.
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I find the on-board computer on my Audi A4 really useful, and leave it set on the 'range' setting. It seems pretty accurate, and when there are 6o miles (estimated) left, the fuel warning sign comes on in the display, plus a 'ping'. I've never dared to run it below 30 miles range, so I can't vouch for this end of the scale.
As I'll be in the wilds of NW Scotalnd next week I'll make sure I fill up with diesel before hitting the more remote areas, where fuel stations can be few and far between and with limited opening times.
Regards
Pat
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The Audi DIS system is reasonably accurate but I wouldn't want to push it beyond 50 miles.
The Ford computer seems to be OK in that it horribly understates the range left....
These things are nice toys but it would be good to have an accurate digital representation of how much fuel is left.
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What about the accuracy of the spelling of 'gauge'? Only joking
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why don't we have "reserve tanks" anymore ?
damned useful.
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I once had a 1971 Mercedes 250 CE. On the motorway the fuel light came on just as we passed a sign saying NEXT FUEL 30 miles.
The car ran out on the slip road leading to the petrol pumps. That was accurate.
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Cardew
The problem is that fuel tanks are nothing like regular shapes on many cars, so calibrating a float in them is very difficult.
As for fuel computer accuracy, the worst I've seen is the Charisma - hardly showed a change in 'miles to empty' from half full to nearly empty.
Usually, you get used to the characteristics of your own car, so it's only a problem in hire cars.
Regards
John
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I use the gauge as a rough guide only, and go on the odometer. In the van 45mpg is 10 miles per litre. If I put 30 litres in it's 300 miles until it needs filling again.
A bit more mpg on the Xantia HDi, so I reckon about 10.5 to 11 miles per litre.
Whilst the shape of the fuel tank will always compromise the linearity and accuracy of the gauge, the important thing (in my view) is to know that the low warning light is reliable.
Ian
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Mark (Brazil)
I second you on the reserve tank concept.
Most motorbikes have one, and they are much easier to push than a car!
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Nothing to do with cars but I recall many years ago when we converted an existing large steel cylindrical tank to use as a 35 sec oil tank for a boilerhouse.
It was mounted on brick piers horizontally.
The fitter made a lovely brass rod to act as a dipstick through the top.
He came into the office later to ask about how to calibrate the markings on it.
Capacity of the tank was easy enough using Pi R2 x H x 6.25 galls per sq ft.
But how do we actually calibrate the rod in gallons.
Remember its horizontal..... halfway down is obviously half...
we buggered about with calculators for half an hour but no-one came up with it.
"wait until the tanker comes in and ask him to stop every 200 gallons, dip it and mark the rod" was the answer given him.
Anyone know....
alvin
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Reserves were all very well. My 57 Conquest Century had 16.5gall tank with reserve of 1.5gall. brought into play by a neat pull knob on the dash which switched the fuel supply to another line from the tank which was set lower than the normal supply. Downside of this system was that as the engine faltered you reached for the knob and pulled and within a few yards you were back in business. Used to do about 26mpg which gave lots of time to forget that the reserve was on so when the engine faltered next time a pull of the knob (the one on the dash) had no effect at all. Believe me the Century weighed in without fuel at 37cwt. This was in the happy days of 4star at 4/9d. per gall.
Not that long ago.!!!
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As soon as my gauge reaches about one third full I look for the nearest petrol station and fill up. Works for me, but then again I'm not driving in the wilds.
Why run the risk of running out of fuel ?
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UEREKA. Well done Mark and thanks....
Archimedes would have been proud of you.....
Actually there was a programme on this man a few nights ago and while I was watching how he worked out volumes of shapes thought your'e just the man I could have used 20 years ago.
At the time when we didn't come up with the answer I later passed it on to the Head of Education in this Establishment and asked him to give it to their maths section. A week later he came down the office and manfully admitted that his fella's couldn't work it out. They took a bit of ribbing to make us feel better.
alvin
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>Anyone know....
>alvin
Ask and ye shall receive..........
www.lmnoeng.com/Volume/CylConeSphere.htm#References>Difficult Sums
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Mark,
Thanks for the link.....I had worked out 90% of the way through this in a coffee break (just for fun) before seeing your message.
I will now check my working.....this takes me back a few years to Uni.
It is absolutely amazing what can now be located on the www with careful use of a search engine.
regards
Ian L.
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I find the fuel range computer in my Focus very handy, have even risked driving with the gauge on empty and relying on the computer telling me how far I can still travel, lowest I've driven it to was an estimated 7 miles remaining and lived to tell the tale. It gives warning gongs at estimated ranges of 50m, 25m, 10m then 0m, which leads me onto my next point...
One thing I've noticed with these fuel range computers in a variety of cars is that if you're running very low and only add say a fiver's worth of juice the computer doesn't pick it up and will rapidly be telling you that you're out of fuel, contrary to the gauge. Slightly annoying...
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Take a Focus and fill it up. Drive 25 miles and the range will have increased by anything up to 50 miles. Same with a Mondeo.
I wouldn't trust these below 50 miles.
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The computer "guesses" range left when you fill up.
Then adjusts according to actual driving (obviously, 5th on motorway is going to be vastltly different to 2nd in traffic).
When I drive the wife's car with nearly full tank, it always says more miles left after driving 20 miles.
This highlights a secondary bonus - it shows tangible benefit of smooth driving style.
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