Is it possible to tell if the actual amounts on the petrol pumps correspond to the amount of fuel put into your tank? I ask this because I regularly fill up at a garage in Watford at 72.9p a litre and do not really notice a difference in the amount I am paying per tank when I use a garage here at 75.9p. This is over the course of 4 months motoring (and a lot of miles). Are the low prices used to entice people like me when in fact the pumps are calibrated on the sparing side per litre. Not accusing anyone, but any thoughts or comments on this would be helpful.
Yoby
I\'ve deleted the specific details of the garage. ND
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If you have any concerns you can ask trading standards to check, but as I understand it, TS are pretty hot on checking the calibration of petrol forecourt pumps.
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TS and the local Petroleum Officer are VERY stringent on calibration checks, however extremes of temperatures can have some affect on accuracy but this is accepted by the authorities.
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I think all pumps have to be calibrated every 6 months?
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groups.msn.com/honestjohn/problems.msnw?Page=1 - Pictures say a thousand words.....
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No info on calibration frequency but however an interesting read www.nwml.gov.uk/consumer/system.asp
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groups.msn.com/honestjohn/problems.msnw?Page=1 - Pictures say a thousand words.....
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Can someone explain to me why diesel is 73.9p at one SHell garage in Luton and at Asda in Watford, and everywhere else in the north london, Luton, MK and Beds areas its about 78.9p?
If it can be sold for 73.9p at one garage surely there should be some competition?
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Craig_1969
Local competition matters. From decades of observation, I find that the large Shell station at the Noke roundabout, south of St Albans, is the cheapest in the whole area, and over the years the commonly agreed explanatory factor for that is the proximity of the cheapo station just down the road to Watford, on the left-hand side after the M25 junction. Similarly, the Shell station on the road down from Luton airport always has the lowest Shell prices in Luton, the explanatory factor in that case being Asda up the hill. Hence, I usually fill up at one or t'other, there being the additional advantage that they are both high-turnover places, so there is little risk of stale and degraded fuel.
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Roger Jones.
I noted your ref to 'risk of stale or degraded fuel' I have often wondered how real is this risk? How long does petrol keep; either in a storage tank at a filling station or,in smaller quantities, in the tank of one's car?
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Cross-ply
I can't speak with any authority on this, but I do believe avoidance of small and under-used filling stations is an HJ recommendation, and I can see the sense in it, although perhaps the associate risks are indeed small. Others may have well-informed technical views to offer.
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A few years ago I did a bit of work for an oil company. There was a rumour/urban myth that their pumps were set to give the most generous definition of a gallon of fuel thereby enabling them to claim that your car would go further on a gallon of their petrol. Not sure how true it is. Also when I worked as a pump attendant in 1970 we used to have the pumps calibrated regularly by a chap who came round with a gallon container and bought a gallon from each pump.
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I was told by a pump service engineer, that they are very, very accurate, and are set to give less fuel than shown, within the legal margin or error allowed by HMW&M.
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Rather disturbing to think that we might deliberately be being given short measure. Given the commodity nature of petrol, this must be an opportunity for a supplier to promote itself with "always full measure" - remember Banks's "a full pint every time"?
A little knowledge on my part is a dangerous thing, and the regs that I haven't the inclination to study are more complicated, but the tolerance as I understand it amounts to minus 1%. Presumably it is difficult to make a dispenser consistently deliver 99% of the indicated quantity so it seems likely that, unless the operator is to run the risk of prosecution, we are rather less than 1% short on average.
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Petrol pump units are potentially highly accurate and use precision-machined piston/cylinder assemblies to deliver a very precise amout of fuel on each stroke (I would be guessing at 1 part in 1000 error, or better). I don't think it would be at all unfeasible to set them to give a consistent 1% short measure. I don't know what the legal tolerance is, but I would be prepared to bet that most pumps are set a the bottom of this tolerance band.
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I'm sure you're correct about the essential accuracy, and on reflection I wouldn't be surprised if the average shortfall is closer to 1% than zero if they are set to exploit the tolerance.
The tolerance applies to all deliveries greater than twice the minimum, but any problem here could easily be aimed-off for by adding an extra "stroke" at the start of each delivery.
Foolish of me to think we weren't being diddled if there's money to be made!
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A variation on this theme has been a bug bear of mine for sometime – it’s this.
When we buy gas the gas bill tells you the calorific value for the gas, calculated each day of the billing period and adjusted for temperature and pressure, so that you pay n pence per kWh. When we buy petrol we get a litre, or possibly less, of something.
Is all petrol refined to an identical standard or is this why sometimes you think that your car is running particularly well/badly.
Cheers
MPZ
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When we fill up a Boeing 747, we always use kilograms as the weight of the fuel is directly proportional to the calorific value, not the volume in litres.
The specific gravity is quoted on the fuel receipt and it varies from around 0.78 to 0.81 depending on temperature, so a 3-4% variance quite possible, mostly a function of temperature. Cold fuel sold in litres is going to be better value for money!
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Cold fuel sold in litres is going to be better value for money!
Exactly the point I was going to raise. The energy supplied by combustion is related to the weight, not the volume. Therefore you should get better value in winter, owing to shrinkage (same volume represents more weight). Does anyone know the likely degree of fluctuation in temperature of bulk undergroung storage?
Oz (as was)
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If anyone has reasonable cause to doubt the accuracy of the pumps at a station, they only have to report it to the local Trading Standards office. When my daughter started with TS she went on the rounds with the battered copper standard measures, checking deliveries.
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>>>Cold fuel sold in litres is going to be better value for money!<<<
Perhaps more likely with a 747 filling from a tanker than a car from a pump? The tanker would be more suseptible to air temperature than an underground tank. I have a vague memory that below 4ft underground the temperature stays pretty much the same.
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I was at the severn Bridge services when the new pumps were being commisioned, the trading standards had a special measuring device to ensure a true gallon was delivered, then a seal was put on the pump, apparently the more the pump gets used the more petrol you get for your gallon, so its in the interest of the retailer to keep getting the pumps checked, if the seal is tampered with then the retailer is in the sticky stuff.
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Personally I'd be happier if TS devoted a fraction of their time to checking the measures in our local pubs, frequently have to ask for top-ups on my pint, and the stuff is now £17.60 a gallon!
Thank God the car only runs on petrol!
Cockle
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I posed a similar query a few months ago although I was more concerned about the 'Minimum Delivery 2Litres' that you see on every pump.
www.honestjohn.co.uk/forum/post/index.htm?t=9627&m...e
Most of the specs and testing criteria are explained on the UK Weights and Measures website. Don't be shy to email them if the info you want isn't there, they were very responsive and helpful to me. One of the few Govt. Depts. I've dealt with that appears to be totally unbiased towards either consumer or supplier.
Kevin...
PS. Consistent over/under-supply from a pump would not obtain type-approval.
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