Filling up ... full tank vs half tank

petrolhead89

DCFC79 wrote: »

or charge a fat tax

:rotfl:a pound for a pound

bartman

I reckon if the place that you use to fill up is on your route anyway, the answer is that you could just put 1/2 a tank in and save a (very) few pennies. Personally, as there are no filling stations on my 50 mile round trip to work and back, I have to make a specific journey to fill up, so I fill the tank.

Having said that, can I make a plea on behalf of the bikers (not being one myself) for drivers of diesel cars not to brim their tanks when they fill up? Diesel fuel is lethal for 2 wheelers when it slops out onto the road, as well as costing you money! I make a habit of stopping at the first "click", and not trying to fill right up to the top of the filler neck.

FATBALLZ

A full tank (55 litres) weighs about 38kg I believe, so you're saving a weight of less than 20kg when you have a half tank. That's about one quarter of a person. I always fill up to the top (not least because I go through a full tank in less than 2 weeks) and never notice any difference between MPG after just filling up and MPG when the tank is nearing the empty gauge.

Of course it will make some difference, but it is so minute that it's a waste of time bothering with unless you have a petrol station in your garage.

KierNet

bartman wrote: »

I reckon if the place that you use to fill up is on your route anyway, the answer is that you could just put 1/2 a tank in and save a (very) few pennies. Personally, as there are no filling stations on my 50 mile round trip to work and back, I have to make a specific journey to fill up, so I fill the tank.

Having said that, can I make a plea on behalf of the bikers (not being one myself) for drivers of diesel cars not to brim their tanks when they fill up? Diesel fuel is lethal for 2 wheelers when it slops out onto the road, as well as costing you money! I make a habit of stopping at the first "click", and not trying to fill right up to the top of the filler neck.

How does it 'slop' out? I fill it up to the top, then put the cap in place...

Lithian

To accelerate from 0-50km/h in 5 seconds (about 31mph) in a 1250kg car needs 121kJ
To accelerate from 0-50km/h in 5 seconds (about 31mph) in a 1275kg car needs 123kJ

climbing hills will also take more energy, to climb 10m takes an extra 2.5kJ
adding rolling resistance at a coefficient of 0.01 you'd need an extra 250J per km

So say in your daily 10km round trip into town you stop at traffic lights 10 times and climb 50 metres you need an extra 35kJ
1 litre of petrol contains about 32MJ and an engine is roughly 25% efficient so it would take you 229 days to waste 1 litre of fuel. At £1.32/litre thats about £2.10/year wasted, but countless trips to the petrol station you don't need to bother with

I've not factored in coming down the hill, you will get some of that wasted energy back but lots of it will be lost to heat through braking so it depends on the road.
Also i've not factored in that you wont always have a full tank of fuel so the cost will go down a bit.

Please feel free to double check my numbers, been a while since i've done high school physics so i could be wrong, hopefully not out by an order of magnitude

vikingaero

If you run one of those horrible French cars that use a FAP filter that relies on a supply of AdBlue/Eoloys fluid then you should only ever fill the car up from fumes to full.

Jakg

How much fuel is lost driving the "extra" distance into the petrol station, idling waiting for a space, starting the car again to move off?

Probably more than you'd save, plus time isn't free. No pont.

bartman

KierNet wrote: »

How does it 'slop' out? I fill it up to the top, then put the cap in place...

The tank has to be vented, air has to be able to get in to replace the fuel used, so putting the cap on doesn't seal it completely.

Here's a link to a campaign of a few years back - it's a big problem, as you will see from a quick Google on the subject
http://www.bmf.co.uk/pages/briefing_room_archive.php?fullstory=406

KierNet

Never heard of that before! Surely its going to be tiny amounts? Unless one person fell off and they wanted a reason for it?

forgotmyname

Still mad queues at my local sainsbury's, Made me wonder why until the guy in front in a 323 petrol bmw
put £7 in. He must have used half that in the queue.