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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: 7,659 Thanks: 2635 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  
Member Joined: Jul 2014 From: Seattle Posts: 96 Thanks: 2  Quote:
 
July 21st, 2014, 02:02 PM  #4 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,659 Thanks: 2635 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 
Member Joined: Jul 2014 From: Seattle Posts: 96 Thanks: 2  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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