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 July 21st, 2014, 12:41 PM #1 Member   Joined: Jul 2014 From: Seattle Posts: 96 Thanks: 2 Fuel consumption advice... I've been hearing a lot recently about only filling your petrol (or diesel as it may be) tank to about half full and making more frequent journeys since the extra mass from the fuel causes an increase in fuel consumption. While I am sure this is true, surely the frequent trips cancel the benefit out even if you incorporate the fuel trips into other longer journeys. I don't have any specific numbers since it will obviously be different for each car but on an intuitive basis, what do you all think? Regards, 3uler.
 July 21st, 2014, 01:05 PM #2 Math Team   Joined: Dec 2013 From: Colombia Posts: 7,683 Thanks: 2664 Math Focus: Mainly analysis and algebra It very much depends on the dry weight of your car plus the items you usually carry. The weight of half a tank of fuel is going to need to be significant in comparison to that for any great difference to be made. Given that petrol weighs 0.7 kg per litre, an 50 litre tank of fuel will weigh 35kg. That's probably less than half of the driver's weight. It's also only about 2.3% of the kerb weight (the car with a full tank of gas, ready to go, with no passengers or luggage) of a family saloon. I reckon you'd do far better to learn a sympathetic and fuel efficient driving driving style.
July 21st, 2014, 01:15 PM   #3
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 Originally Posted by v8archie It very much depends on the dry weight of your car plus the items you usually carry. The weight of half a tank of fuel is going to need to be significant in comparison to that for any great difference to be made. Given that petrol weighs 0.7 kg per litre, an 50 litre tank of fuel will weigh 35kg. That's probably less than half of the driver's weight. It's also only about 2.3% of the kerb weight (the car with a full tank of gas, ready to go, with no passengers or luggage) of a family saloon. I reckon you'd do far better to learn a sympathetic and fuel efficient driving driving style.
This is what I'm thinking, I'm certain there is a difference but it's got to be so minute that it is quickly cancelled out by increased trips to fill the tank. According to the article in The Guardian, "Strip any excessive weight from your car – even fuel. Every 45kg removed from the car can save 1% on fuel. It could be worth experimenting with not filling your tank to the top and instead filling more often." but obviously you've got to have enough fuel for a given journey. Driving style was mentioned in the article too, you can find it at: Get the most from your car with these top 12 'hypermiling' tips | Leo Hickman | Environment | theguardian.com if you wish to read the other recommendations. I already do, I'm pretty laid back so it is my natural driving style anyway especially in comparison to the way most people drive today haha. I am not really worried about saving more fuel, just thought this claim was interesting.

 July 21st, 2014, 02:02 PM #4 Math Team   Joined: Dec 2013 From: Colombia Posts: 7,683 Thanks: 2664 Math Focus: Mainly analysis and algebra I'm sure it would save you something (as long as you don't have much of a drive to find fuel), but 45kg is a pretty huge amount of weight to get rid of and 1% is a pretty meagre saving. I don't think I'd find it to be worth the hassle.
July 21st, 2014, 02:45 PM   #5
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 Originally Posted by v8archie I'm sure it would save you something (as long as you don't have much of a drive to find fuel), but 45kg is a pretty huge amount of weight to get rid of and 1% is a pretty meagre saving. I don't think I'd find it to be worth the hassle.
Yes, I agree. Thanks for the replies.

 August 25th, 2014, 09:28 AM #6 Newbie   Joined: Jan 2011 Posts: 3 Thanks: 0 Everything little adds up. I have taken part in an eco driving course and under instruction from the instructor I managed to go from 41 mpg to 51 mpg, which at the time was around 20pence per liter saving at the pump. If you add another percent on that and anything more you get is great, but as stated before your driving style makes a much bigger impact.

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