How can I accurately calculate MPG given that I buy petrol in litres ?
Would appreciate advice.
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4.5 litres = 1 gallon.
Therefore calculate as follows:
Miles covered
(litres of fuel used /4.5)
= MPG
EX
400 miles
(45 l = 10 gallons )
= 40 mpg
P*ss Easy
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You did say you wanted an accurate figure--so you need to divide
the litres by 4.546
And of course you should record the mileage full tank to full tank.
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If you want to get really accurate you should divide by the reciprocal of 0.22, or 4.54 recurring. Or to make life more simple, multiply by 0.22.
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After many years calculating MPG I now calculate MPL, which seems reasonable as hardly any garages sell gallons these days. On that basis 10 mpl seems good (45 mpg), 12 for a diesel (55 mpg). An almost exact conversion is 11 mpl = 50 mpg. Does that help?
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To obtain accurate MPG figures, you must fill your tank up to exactly the same level each time. In practice, this means you must fill right to the brim each time, and make sure the petrol station forecourt is dead level. Obviously the amount you put in is then exactly the amount you have used since you last filled up.
The accurate figure for conversion is 4.54609 Litres to the gallon.
Mike Humpherson. (Hopeless pedant!)
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Bloody hell Mike, you're worse than me! In practice rather than trying to get accurate readings on one tank full, which as Mike points out isn't easy or accurate, you need to measure fuel consumption over a reasonable mileage - 500 to 1000 miles. Start by brimming the tank (don't include this fuel in the calculation), and note the mileage. Then record every litre added, even if its's not full every time, ending by brimming the tank again, noting the mileage when you do it (include this last fill in the calculation). Divide total miles by total litres over the mileage, multiply by 4.55 and you have a good idea of the overall fuel consumption of the car in miles/gall. This saves the need to carefully brim the tank every time.
regards
john
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I get 700 miles to the tankful with my Peugeot 405 Turbodiesel, and I calculate the MPG on every tankful. The more often you calculate the MPG, the easier it is to correlate any change in MPG to the type of journey you have been doing or to any problem with your vehicle.
Mike Humpherson.
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Mike
Yes, sorry, I forgot you economical diesel drivers! Fair comment, but I was making the point that you can carry out consumption checks over several tankfulls - it doesn't have to be just one.
Regards
John
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Obviously although I never explained how to measure " Fuel USED " it would be the amount taken to fill the tank again after the mileage covered.
It's not rocket science.......
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All good stuff, guys, but don't forget to check accuracy of recorded miles. I have had several cases where mileage was under-recorded, making consumption look bad when it wasn't. I think we covered this in an earlier thread, but comparison with another vehicle over a set route is useful, as is distance between services on motorways.
Regards, Adam
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This is taking us back to the recent thread about how far the tank should be filled. Rather than brimming the tank (extra weight, remember?) I usually put in 20 or 25 litres, then when the gauge shows exactly half (or a quarter - it doesn't matter which, just any reference point on the gauge) note the odo-reading to the nearest 5 miles. If you remember to do this after every 'fill' you can monitor consumption regularly. I find answers reproduce within 2-3 percent - no more erratic than the effect of long/short journeys, speed, weather, etc.
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I fill my two tanks in my toyota prado and it takes 32 gall...yes in the UAE we still have real measurments....and it costs £20.00 quid....and i dont have to get out of the car..and i get the windshield cleaned as well.......
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Or 20mpl for a motorbike! (90 mpg)
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With most +500cc machines offering 40mpg (8.8mpl) or less, the quote of 90mpg may be more appropriate for the step-thru generation.
Honda Cub, anyone?
No, I thought not.
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Sorry - I can't get my head round MPL. I think I'll stay with good old MPG that we can all understand.....
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Neil
Not a Cub, but you are right, it is a Honda.
Actually a CD250U. My second of that model on which between them I have clocked up 100,000 miles.
I used to get 110 mpg out of its' predecessor, the CB200 Benly, but got shot of that because the 6v, 35w headlight was positively dangerous at night on a 20 mile out of town dual carriageway run.
I used to have to drive slowly until another vehicle came past at the speed I wanted to travel at, tuck in 20 or 30 yards behind it and follow it until my slip-road came up.
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Why?????????????????????????
There are far better things to do with your time such as chasing ladies & drinking beer.
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I really am getting worried now. Counting distance markers on a dual carriageway? Deciding on which pump to fill up on because it is used more often?
Come on Gents - please get real. How many of you bean counters (not flickers) accelerate gently away from junctions/anticipate gear changes/always select the correct gear/drive at a constant 56mph?
At the end of the day, your car will do +/- 5mpg whatever you are getting regardless of what pump you use or how you calculate it.
Park the car up, go to the pub and have a few beers and then calculate how many steps it takes you to get home. If the answer is "More than it took me to get there" - you have had a good night.
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When I used to retail petrol the figure I used to used was what Mike has already put one gallon = 4.54609 litres.
If you really want to increase your MPG or MPL choose a filling station with Gilbaco pumps rather than Tokheim. Also choose the most used pump (usually nearest to shop door).
The meters on Gilbacos pumps give more measure as they wear over a long period whereas (it was alleged) the Tokheim type of meter used to wear the other way and give reduced measure.
I am not an engineer but was told it was just the type of meter used.
Each year when the local council W&M did the annual check my Gilbaco pumps often had to be adjusted as we were giving over measure (too much fuel per indicated gallon/litre).
A Filling Station nearby used to boast that his Tokheim pumps gave such a short measure on the annual W&M check that W&M always broke the seals and adjusted them to give more fuel to the customer. His boss said the Tokheims gave him a free holiday each year!
Nothing illegal you understand but just the way the meters behaved when pumping huge volumes. This was with petrol ,derv seemed to lubricate the pumps and remained fairly static in measure.
Also remember it was a tiny amount per sale, an eggcupfull at most either way, but with the huge volumes it mounted up.
I used to lose a tanker of fuel ,6000 gallons, each year to wet stock loss which comprised evaporation (very little) and over measure pumps.
This was 15 odd years ago but perhaps someone else can confirm if the same thing happens now.
Martin
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One more thing to check is the odometer. They can easily be a few % out.
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Re : odometer check
I checked my Focus Tdi, as discussed in an earlier thread, against 161 of the 100m markers on a dual carriageway (s/be exactly 10 miles).
It came out at 9.8 miles on the odometer, so I am reading only 2% 'slow'.
Disappointing, as I was hoping it would explain the high fuel consumption figures I get!
But it IS a good way to check!Tim Hirst wrote:
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OOPS!
Sorry, Tim, got a little unwanted bit in there!
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Gentlemen!
Reading this thread I promise to take back everything I have ever said about bean counters!
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A couple of thoughts:
Watching fuel economy figures too closely will drive you insane. Unless you are a lucky fellow with a good diesel engine you really don't want to know how much all those little journeys are costing you.
How accurate are the fuel enconomy meters that are included with the computers on a lot of cars (the average consumption readings not the real time ones)? I've used these to gain a ball park figure and they seem to be OK.
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