There is a lack of parity between my mpg on my trip computer and my own calculations. Is this normal or am I doing some flawed maths?
During mainly Urban driving since resetting the trip at fill up last week I have averaged 45.9mpg according to the computer.I have topped up up today,divided the number of miles done since last top up by number if litres and multiplied by 4.546 giving 39.39mpg showing a difference in economy of 16%. Its a corolla diesel
Any reason for such a difference?
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My Alfa's computer is similar (though not at those levels!) The trip computer says Im getting about 27-28mpg on average. I do brim to brim fill, and calculate around 24-25mpg.
Not sure if this is the case, but mine doesnt seem to register any fuel use whilst idling (ie actual mpg goes to --). Dont know if this would make that much of a difference?
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Actually mine doesn't register during idling on the continuous mode so this may be skewing the results, I spend a fair time at a standstill every day!
Just found out my pre purchase brochure which lists the Urban figure as 39.2 so I guess I'm fractionally in credit!
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Measured over several brim to brim tankfulls my VW computer is optimistic by 3-4% ie shows approx 1mpg more than the brim to brim figure. SWMBO's Toyota Yaris is pessimistic by 4-5%.
The worse computer I have had was in a Primera. The predicted range left could drop by 50 miles in a couple of miles driving. It didn't seem to use the average or instant consumption figure for that calculation.
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I understand the wish to check accuracy, but speaking as a biker, I wish drivers wouldn't brim fuel tanks. In fact I wish it was impossible to...
Sorry to hijack the thread, but this is something guaranteed to get me on my Hobby Horse.
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For your piece of mind I don't 'brim' it .When it clicks off,thats enough for me.
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For your piece of mind I don't 'brim' it .When it clicks off,thats enough for me.
That's all very well if you use the same pump time after time. All pumps trip off at different rates.
The garage down the road is a right PITA, once you've got more than a fiver in the tank, you have to reduce the flow right down to a trickle, otherwise it continually trips off, and when you do eventually fill the tank, the sensor doesn't trip off the pump and you end up with a shoe full of petrol. I only use this garage if I have to.
The other garage I regularly use, once tripped for the first time, I can get anything between £1.50 to £4's worth of petrol in afterwards, depending on which of the 4 pumps I use to fill up with.
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In my Fabia tdi, there is a very nearly hidden button on the RH side of the filler tube. If you press this when filling, the tank will accept around 5 extra litres from normal "brimful", never mind "first click off". I only found this out, after nearly three years of ownership! ), after it was mentioned on www.briskoda.net
jolly useful feature when filling with diesel at Safeway, Gibraltar, where the price can be as low as 30 pence per litre, depending on one's store spend!
Roger.
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My C5 2.0 HDI always underreads by 2-3mpg, 2mpg when it reads about 38 on the display, 3mpg when showing closer to 50mpg.
The average consumption does decrease when you sit idling the engine. This is seen after resetting, driving along then idling at traffic lights.
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Omega is also optimistic by about 2-3 mpg
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Malteser - Going slightly off thread but still to do with motoring , how do the prices of Petrol and Diesel in Gib compare with Spain these days? Is it still worth the wait in the queue at the border?
You could very nearly run your car cheaper on the Japanese whisky they sell in Main St - Gibraltar than on petrol in UK!
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Helicopter
I only look at diesel, but in Spain it's about 0.69 euros per litre which mas o menos works out at £0.48 to £0.49 per litre.
The base price in Gibraltar seems to be about £0.35 to £0.38 per litre. If you spend money at the Safeway store before filling at their service staion, you can get money of the fuel - I have had £0.10 per litre discount which gave a net of around £0.28 per litre.
At this time of year with no "guiris", (grockles in UK),about; at 9 am it's nearly straight in and if one leaves around 11:00 to 11:30 it is nearly always straight out. The Spanish customs are only interested in cigarettes at present and they always ask if you have any. If you are young, a group of lads or lasses in a grotty camper van, or any one in a 4WD with blacked out windows they will turn you over big time!
Roger.
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Roger,
I know Gib very well indeed as a sailing base with my family and have anchored in Marina Bay and filled up hire cars many times at Safeway in the Europort.
Fuel was always cheaper in Gib than Spain and talking of cigarettes I used to sit on deck and watch the blacked out 4wd's load Marlboro's and possibly other substances into black ribs ( rigid inflatable boats) with 2 x 1000cc Yamahas which left Gib going to the more deserted coast of Spain.
On more than one occasion we heard gunfire as Spanish customs in hot pursuit. This sounds fanciful but its absolutely true.
Gib used to turn a blind eye but I believe one day the police just came and impounded all the smugglers boats without warning.
Do you know the Terrazo at Casares?
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We love Casares - it's only a short way from where we live, but when we can afford to eat out we stay in our little,(but growing), seaside village so we can walk home afterwards!
Roger.
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You must be somewhere near Manilva then, and IIRC the drive from the N340 there to Casares used to be quite hair raising without even having a drink, but I believe they've done a bit of straightening and resufacing now. The view is wonderful from the Terrazo on a clear day with the village in front of you and the mountains in the distance and a glass or two of tinto verano.
We have moored up at Puerto Duquesa on many occasions and quite often had the dolphins swimming in the bow wave of the boat so close you could practically touch them.
Some nice restaurants there as well - I love the seafood.
Anyway - I envy you...although its not so nice when you get the forest fires and you are getting ash dropping in the Paella!
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As Mae West may have said - loosly paraphrased " Come up & see us sometime"!
Roger.
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Have to take a rain check on that Roger - at the moment the boat is moored in Portugal and the next helicopter holiday is already planned to Madeira after a visit to the middle east next month.
Life is a bit hectic and I have to earn a crust. I'll just have to dream for the moment of those Prawns pil pil, also the doctor has just more than hinted that a diet might be in order together with a distinct reduction in alcohol and cigar intake. They always have to spoil things don't they.
- Anyway we've also strayed a long way from the thread so the mods will be after us.I'll see you down the Gym!
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Not likely - I DRIVE everywhere! (See, back to motoring in one fell swoop!)
Roger.
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I am never sure how acurate brim-to0brim figures are. I am not sure about petrol but often with my diesel it can be very frothy and cut off when I know that I can fit another 10 ltres or so in. If I felt like standing by the car for 10 minutes until all the air bubbles had come out then I am sure that I could get an accurate figure.
Also with brimming you never know if there are air locks in the tank. I have brimmed to what I thought was full and then rocked the car and had lots of air come out.
Say you have a 60 litre tank and there is 1.5 litres "missing" from a brimmed tank this will exaggerate the figures by 2.5%
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I use two methods to monitor consumption: (1) if the gauge behaves reasonably sensibly, make a mental note of the odo reading when the needle passes a certain mark (I use quarter-full). Usually accurate within 10 miles or so. For proper scientific calculation, plot these figures against total litres and measure the slope of the line. (2) knowing the expected consumption, always buy the same amount of fuel, which you aim to cover a round number of miles, to simplify calculation. On the 306 HDi I always buy 22 litres, target 300 miles (=62mpg). Doesn't often happen in winter!
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Agree totally. Brim to brim entirely dependent on pump, weather etc. Easily half a gallon in it, sometimes more.
Chosse a mark on the petrol gauge, you'll be surprised how quickly the needle goes past the mark. I use 3/4 full myself.
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Trip computer on the laguna is about 5% optimistic. It seems that most cars are not 100% accurate in the trip computer department. _ not a problem per say, they can still be usefull once you have worked out how accurate they are.
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Nissan Micra SE, 2004 version, take 10% off the computer reading for a much more realistic figure.
I fill just past the gauge full mark and then when the needle has fallen back to being dead centre of the full mark, I read the miles and then zero the reading.
I don't need to watch the gauge whilst filling. I can mostly guess near enough what to put in as the tank takes quite a bit after the gauge needle reads full.
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My Laguna II Tourer diesel was 10% optomistic, Passat 110 diesel was 5% optomistic, current Golf 110 diesel is more or less spot on (checked by tank brimming/trip milometer).
The venting button in the filler neck seems to be common to nearly all VAG cars (not Galaxys - Ford filler?). Using it to vent tank gave an extra 20 litres in the previous model Passat Estate! However, brimming does take up the expansion space so don't do it if you are going to park immediately after filling. I've never noticed any problem with the various VAG cars, whereas brimming my Sierra (many, many moons ago) in the summer would have it incontinently dribbling petrol before I'd managed to pay at the cash desk. Very quickly gave up that practice with that car...
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