New thread on 'Top Tier' gasoline...

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Mike Marlow wrote:


Besides the improvement in gas mileage, he got a great price.
I would have expected to pay closer to $550.29 for all that work.
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Don't you mean $550.299?
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Elmo P. Shagnasty wrote:

Now you're splitting hairs.
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Elmo P. Shagnasty wrote:

And the temperature volume compensation thingy on the gas pumps here in Ontario.
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<Puke...> I curse the idiotic soccer mom that ever came up with that term "thingy".
--

-Mike-
snipped-for-privacy@alltel.net
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Mike Marlow wrote:

call it, but I certainly despise it. Every time you pump gas, it automatically adjust the volume reading to what it would be if the temperature of the fuel was 15 degrees centigrade. As a result, there is no way of knowing exactly what volume of fuel you have put in your tank. Mind you, I suspect that the temperature of underground storage tanks does not vary a great deal from one day to another unless it has been recently topped up from a delivery tanker that has been exposed to temperature extremes while on the road.
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wrote:

I'm amazed at all the people quoting fuel consumption to the nearest 0.01 mpg. What are these figures and how are they obtained? I presume they are with an mpg gauge fitted to the car, rather than from measuring the amount of fuel required to brim-fill the tank from when it was previously brim-filled, and the distance travelled on that tankful.
So are they instantaneous readings in identical conditions (eg 70 mph on the same level route at 20 deg C with no cross/head/tail wind). Or are they averages over the same journey.
Measuring my consumption by the fill-tank-and-note-distance method, over about 550-650 miles, I get results which can vary by +/- 3 mpg depending on variables such as route and mix of urban/rural/motorway driving and on different cut-off points of different pumps.
http://img239.imageshack.us/img239/7892/fuelconsumptionul1.png
The results are for a Peugeot 306 HDi (turbo-diesel) with manual transmission, using mainly "supermarket brand" (Sainsbury's, Tesco, Asda) Ultra Low Sulphur Diesel (ULSD), with occasional use of branded fuel (eg Shell, Esso, BP, Total).
It's reassuring the see that over nearly 130,000 miles, there hasn't been a noticeable reduction in the mpg as the car has got older: the only significant change was that the consumption was worse when the car was new until the engine got thoroughly run-in.
The figures are miles per UK gallon, so multiply them by 4/5 to convert them to US gallons.
The blue points/lines are the actual readings for successive tankfuls. The red line is a moving average over three values. The pink line (at just under 50) is the overall average since new: total distance / total fuel.
The readings of around 58-59 are for long motorway journeys at 70 and then journeys at around 50m, with very few short journeys or around-town driving, when I was on holiday. The rest are a random mix of journeys at 30-50 for about 15 miles, with a few longer ones thrown in. I don't have a need to do much travelling in heavy traffic, so there isn't the frequent stop/start/sit-in-traffic-jam component.
Interesting that the results were consistently bad (41-44 mpg) when the car was new until the car was about 7 months old and had done about 8000 miles. That's a long time for the engine bearings to slacken off!
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decimals. The method I've used is at the start of a trip the first fill is to the brim, and write down the odo reading. Every other fill is to an even gallon on the pump until I get home when I fill to the brim again, and jot down the final odo reading. On the trip I fill to the even gallon, 10, 11, 14, whatever, and jot it down. I don't worry about a couple hundredths if I go over an even gallon, and don't bother with the odo again until I'm back home. So at the end I've done 2533 mile and used 81 gallons. Doing a division using Windows calculator I get 31.271604938271604938271604938272 mpg. Of course I would say if asked my trip mileage, "A tad over 31." If I do the same trip next year in the same car it should be close to the same, so I pretty much know my gas costs. I would trust this method more than any onboard car fuel metering device, but know it's not perfect. Weather, driving conditions, tire size/inflation, etc, etc. Frankly, I only do this once after I get a car to establish a reasonably close expectation of mileage. After that I just gas when needed, and hardly ever think about it. Those who want to measure mileage could do the same on a yearly basis and be pretty confident about their overall mileage. I don't know how the car consumption meters operate, but it would be interesting to see the variance over a year between what they say and what was actually pumped into the car according to the gas pump meters. My impression of the calibration of the meters on the gas station pumps is that it's good. I'm pretty sure there are plenty of volunteer "consumer watchdogs" with exact gallon cans checking them out, and itching to go after the oil companies if they are overmetering. But maybe they are undermetering a bit to keep them off their backs. It could cost them quite a bit if they were caught shorting the public.
--Vic
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I'm absolutely positive that the results of your "simple division" create results with FAR more numbers to the right of the decimal point than what you've given us.
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yeah. The engine computer has absolutely NO idea how much fuel is going through the injectors.
Dumb computer.
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yeah, those stupid engine computers and management systems are far, far less reliable and precise than any random gas station pump you run into.
Uh-huh.
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Two tankfuls does not make a very good trial. In order to compute variance of a measurement you should take about ten, and compare the resulting variance to the differences between milage with different gases. A difference less than the variance is meaningless. Fortunately, many calculators these days will compute variance as well as average, so the statistics are a lot easier these days.
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Hachiroku $B%O%A%m%/(B wrote:

But you live in Massachusetts, far from there.
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On Sun, 03 Aug 2008 19:09:36 -0700, larry moe 'n curly wrote:

Ah, yes, this is true...
OH! Wait!
"Gulf Oil Limited Partnership, now based in Newton, Massachusetts is a wholesaler of refined petroleum products"
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