Full tank vs frequent visits to petrol station

FrankC21 · 26-03-2021 2:28pm #1

Hi,

One of my mate at work - a big car enthusiast - gave me an advice against puttin €20 each time I go to the petrol station, he said that I should fill up the tank up to the brim. I usually put €20 and when it nearly gone put another €20, I kinda think I will save money this way.

His reason is that if I do not do this, I keep releasing the built up/gas pressure each time I visit the petrol station and that pressure/gas is the actual diesel i paid for, evaporating out into the air.

Is that an actual fact? He recently change his car from 2007 petrol RAV4 AWD to a nissan 1.5 dci deisel and a full tank will last him 2-3weeks.

Doctors room ghost · 26-03-2021 2:31pm

Your friend is talking pure waffle

Atlantic Dawn · 26-03-2021 2:37pm

There might be some saving if you were driving in an urban area passing multiple fuel stations so no risk of running out and kept tank at 25% full, each litre of fuel is an additional kg weight in the car, savings would be in the single figure €'s over a year.

bazz26 · 26-03-2021 3:07pm

FrankC21 wrote: »

Hi,

One of my mate at work - a big car enthusiast - gave me an advice against puttin €20 each time I go to the petrol station, he said that I should fill up the tank up to the brim. I usually put €20 and when it nearly gone put another €20, I kinda think I will save money this way.

His reason is that if I do not do this, I keep releasing the built up/gas pressure each time I visit the petrol station and that pressure/gas is the actual diesel i paid for, evaporating out into the air.

Is that an actual fact? He recently change his car from 2007 petrol RAV4 AWD to a nissan 1.5 dci deisel and a full tank will last him 2-3weeks.

pippip · 26-03-2021 3:11pm

argument is usually the effects of carrying the extra fuel of a full tank around versus not.

Personally I pass alot of fuel stations so will only full fill when I notice a good lower than average price.

FrankC21 · 26-03-2021 3:13pm

bazz26 wrote: »

He change his car cause the RAV4 is very thirsty, he lives in wicklow and works in Dublin, he switch to diesel cause of the commute.

He owns about 13 vintage cars mostly mercedes. Mad fella.

GreeBo · 26-03-2021 3:19pm

If a petrol station is on the way home to your house then no real difference, but if you have to go out of your way to fill up then you are actually wasting money/fuel.

Bass Reeves · 26-03-2021 3:33pm

OP friend is fairly right. First starting and stopping a car uses more fuel. Even the act of pulling into and out of a garage uses fuel. 20 euro's worth is equivalent to about a quarter tank of fuel. That is four fills to every full tank of fuel. OP is starting and stopping a car 4 times instead of once.

Filling a tank is equivalent to carrying a half a tank of fuel with you all the time. A quarter tank is equivalent to carrying an eight of the tank all the time. It's equivalent to carrying an extra 20 kgs around in your car. This will have very little different on fuel economy.

On OP friends point about trapped gas he is correct. If you spill a small bit of petrol on the ground it evaporates. An empty tank will fill with petroleum gas. That why you should never smoke when filling you car with fuel especially petrol.

At best Op you are saving nothing however IMO what you are doing is costing you money

frozenfrozen · 26-03-2021 3:33pm

I get range anxiety if I don't have a few hundred kms of fuel so it always gets brimmed

26-03-2021 3:36pm

I always just fill to the brim.......... usually from 1/16th full.

grogi · 26-03-2021 3:39pm

FrankC21 wrote: »

Hi,

One of my mate at work - a big car enthusiast - gave me an advice against puttin €20 each time I go to the petrol station, he said that I should fill up the tank up to the brim. I usually put €20 and when it nearly gone put another €20, I kinda think I will save money this way

Savings are there (you are not ferrying around weight of the fuel) but it is minimal.

You're however wasting a lot of time getting to the gas station three times as frequently as needed.

Akesh · 26-03-2021 3:39pm

This is completely false. While there would be some evaporation when you open your tank, the benefit of carrying less fuel would greatly offset this impact.

Thinkingaboutit · 26-03-2021 3:45pm

FrankC21 wrote: »

Hi,

One of my mate at work - a big car enthusiast - gave me an advice against puttin €20 each time I go to the petrol station, he said that I should fill up the tank up to the brim. I usually put €20 and when it nearly gone put another €20, I kinda think I will save money this way.

His reason is that if I do not do this, I keep releasing the built up/gas pressure each time I visit the petrol station and that pressure/gas is the actual diesel i paid for, evaporating out into the air.

Is that an actual fact? He recently change his car from 2007 petrol RAV4 AWD to a nissan 1.5 dci deisel and a full tank will last him 2-3weeks.

I just fill up as I don't like having to go to a petrol station stinking of fuel and bad food.

Bass Reeves · 26-03-2021 3:47pm

grogi wrote: »

Savings are there (you are not ferrying around weight of the fuel) but it is minimal.

You're however wasting a lot of time getting to the gas station three times as frequently as needed.

Not just time but fuel as well. The physical act of stopping and starting a car uses fuel. And IP friend is right about fuel evaporation when it turns to into a gas especially in hot weather. Why do you think there is such a deal on fuel tanks

FrankC21 · 26-03-2021 3:49pm

But if you have a full tank, you're more likely to "pedal to the metal".

Alun · 26-03-2021 3:51pm

Atlantic Dawn wrote: »

There might be some saving if you were driving in an urban area passing multiple fuel stations so no risk of running out and kept tank at 25% full, each litre of fuel is an additional kg weight in the car, savings would be in the single figure €'s over a year.

1 litre of water weighs 1kg, petrol is less dense and weighs around 770g per litre.

Kopparberg Strawberry and Lime · 26-03-2021 3:52pm

Leaving the fuel difference aside

Why would you want to go to a pump twice a week when you could only need to go once Bi-weekly

Just wasting time alone at a pump, other pump users , the inconvenience of a few mins when you can just sail on to your destination with a healthy tank !

Islander13 · 26-03-2021 3:54pm

Surely the time wasted faffing about in a petrol station and these days being exposed to COVID risks (however minor) mean filling to the brim a no brainer

WacoKid · 26-03-2021 3:54pm

I always take the approach:

Don't continually run on low fuel as you are dragging the dirt from the bottom of the tank through the system.
Let the tank run somewhat low before refueling so you are not keeping old fuel in the tank. Constantly filling up from 1/2 to full means there is fuel there that is never getting burned off, or a least taking a long time to do so.

Boardnashea · 26-03-2021 3:56pm

There is also the risk of dropping an extra €5 on coffee/choc/flowers for the Mr/Mrs (or both). Think of the waistline!

26-03-2021 3:56pm

I fill to the brim every time because, frankly, petrol pumps are disgusting and the fewer times I have to have one in my hands the better

26-03-2021 3:58pm

frozenfrozen wrote: »

I get range anxiety if I don't have a few hundred kms of fuel so it always gets brimmed

You're going to have a heart attack when we all have to drive EVs so!

The J Stands for Jay · 26-03-2021 4:00pm

My parents looked into this in the 80s, on a diesel Peugeot. They drove something like Sligo to Dublin only putting in a bit of fuel at each stop, and then on the way back brimmed it. No decent roads back then, don't was a long journey. Not filling it was actually cheaper, but they decided they'd rather have a slightly higher cost than stopping more often.

yabadabado · 26-03-2021 4:08pm

I always fill it up and then let it get near empty,I pass several stations going about my daily business but wtf would you want to be messing around with filthy pumps more than is necessary.

CoBo55 · 26-03-2021 4:26pm

WacoKid wrote: »

I always take the approach:

Don't continually run on low fuel as you are dragging the dirt from the bottom of the tank through the system.

Let the tank run somewhat low before refueling so you are not keeping old fuel in the tank. Constantly filling up from 1/2 to full means there is fuel there that is never getting burned off, or a least taking a long time to do so.

First part yes.
Second part no, the new fuel mixes with the existing fuel.
I let mine down to when or just before the light comes on usually 1000 to 1100km put in my 60ml of miller's diesel additive and fill her up it's always very close to 60 litres. Couldn't be bothered with 20 here and a tenner there...

Del2005 · 26-03-2021 4:26pm

WacoKid wrote: »

I always take the approach:

Don't continually run on low fuel as you are dragging the dirt from the bottom of the tank through the system.

Let the tank run somewhat low before refueling so you are not keeping old fuel in the tank. Constantly filling up from 1/2 to full means there is fuel there that is never getting burned off, or a least taking a long time to do so.

As you pour the fuel in it'll be mixing with the old fuel and once the car moves then it'll be all mixed together, all fuel is millions of years old.

At the end of the day it's a trade of off saving a few cent by not hauling extra weight in fuel* vs having to spend more time at petrol stations. If your tight for cash and have loads of time stick €20 in, if your tight for time brim it.

* For the majority of people who stick €20 in they'd save more by checking tyre pressure, getting the car serviced and emptying all the crap they have out.

Leonard Hofstadter · 26-03-2021 4:30pm

Life's too short to be spending lots of time at petrol stations re-filling a car all the time. This is one of the reasons I don't like EVs, even the ones with decent range still need at least half an hour to recharge when low on battery.

Aside from that, brimming every time means it's possible to work out exactly what the fuel economy is, so it's much easier to pick up on whether your car has an issue if you know how much fuel you've used since you last filled it up - and the only way to do that accurately is if you fill it every time, note down how many litres were needed to re-fill it and the distance travelled since the last fill up.

hashbones · 26-03-2021 4:30pm

filling your tank to the brim, your literally burning fuel to carry your fuel. if the distance you have to travel to the station is out of your way then thats a different matter based on how far that is. if your passing the station daily then small fill ups are the way to go.

purely from a factual point of you. i dont think the majority care either way

tayto lover · 26-03-2021 4:31pm

Any savings would be less than a €1 I’d say.
Hardly worth the trouble.

CoBo55 · 26-03-2021 4:32pm

Leonard Hofstadter wrote: »

Life's too short to be spending lots of time at petrol stations re-filling a car all the time. This is one of the reasons I don't like EVs, even the ones with decent range still need at least half an hour to recharge when low on battery.

Aside from that, brimming every time means it's possible to work out exactly what the fuel economy is, so it's much easier to pick up on whether your car has an issue if you know how much fuel you've used since you last filled it up - and the only way to do that accurately is if you fill it every time, note down how many litres were needed to re-fill it and the distance travelled since the last fill up.

Good point about the fuel economy, mine always improves as we move into this time of year.

Bass Reeves · 26-03-2021 4:48pm

hashbones wrote: »

filling your tank to the brim, your literally burning fuel to carry your fuel. if the distance you have to travel to the station is out of your way then thats a different matter based on how far that is. if your passing the station daily then small fill ups are the way to go.

purely from a factual point of you. i dont think the majority care either way

You are forgetting to factor in momentum, mass from physics and the physical starting of an engine.

tcawley29 · 26-03-2021 4:49pm

FrankC21 wrote: »

But if you have a full tank, you're more likely to "pedal to the metal".

Ah here, you're talking nonsense at this stage. As usual

FrankC21 · 26-03-2021 5:06pm

tcawley29 wrote: »

Ah here, you're talking nonsense at this stage. As usual

Ah, did I upset you.

newmember2 · 26-03-2021 5:08pm

FrankC21 wrote: »

Hi,

One of my mate at work - a big car enthusiast - gave me an advice against puttin €20 each time I go to the petrol station, he said that I should fill up the tank up to the brim. I usually put €20 and when it nearly gone put another €20, I kinda think I will save money this way.

His reason is that if I do not do this, I keep releasing the built up/gas pressure each time I visit the petrol station and that pressure/gas is the actual diesel i paid for, evaporating out into the air.

Is that an actual fact? He recently change his car from 2007 petrol RAV4 AWD to a nissan 1.5 dci deisel and a full tank will last him 2-3weeks.

I agree, the more times the petrol tank is opened the more evaporation.

yabadabado · 26-03-2021 5:09pm

hashbones wrote: »

filling your tank to the brim, your literally burning fuel to carry your fuel. if the distance you have to travel to the station is out of your way then thats a different matter based on how far that is. if your passing the station daily then small fill ups are the way to go.

purely from a factual point of you. i dont think the majority care either way

What would it actually be costing to carry the extra weight?
I've no idea but I'd presume it's negligible over the course of a year .The extra few turns into the forecourt and stop/start probably takes care of it.

DaveyDave · 26-03-2021 5:18pm

Stop half filling your car and going back to the petrol station unnecessarily. The extra weight of 20 litres of fuel is nothing compared to the weight of the car and driver. You won't notice the fuel consumption. Fill your car and feck off

diceyreilly · 26-03-2021 5:20pm

Put €20 + and change i have in the car when i am there.

Montage of Feck · 26-03-2021 5:22pm

Constantly running low isn’t good for the fuel system.

Bass Reeves · 26-03-2021 5:32pm

yabadabado wrote: »

What would it actually be costing to carry the extra weight?
I've no idea but I'd presume it's negligible over the course of a year .The extra few turns into the forecourt and stop/start probably takes care of it.

You would be carrying about an extra 20 kg on average. Considering a fairly average car with two people in it weights about 2 ton, 20 kgs is less than 1%, of the gross weight.

Fuel efficiency is also effected by aerodynamics and tyre pressure as well as other factors an extra 20 kgs will use less than 0.5%extra fuel. In a car that takes 60 litres that's about 0.3L/fill if car is filled to the brim every time compared to 1/4 filling a car.

Starting a car uses fuel. The physical act of getting a car moving( think about trying to push a car it takes more energy to get the car rolling than to keep it rolling) using extra fuel as well as getting it back up through the gears to a road speed.

Finally you have evaporation. A petrol tank is a sealed tank so it holds any petroleum gas within the tank. If you ever open a gallon that holds petrol for a lawnmower or chainsaw especially in hot weather you will literally see the gas escaping. Exactly the same happens when you open a tank of a car.

dmc17 · 26-03-2021 5:39pm

There's more hot air escaping from your friend than your petrol tank I reckon

MrMusician18 · 26-03-2021 5:45pm

I wouldn't think there is much difference but certain cars use a fuel additive called Eoly's and that's delivered to the fuel tank every time you open and close the fuel door. While the amount added depends on the quantity of fuel in the tank, more frequent fuelling results in this rather expensive additive being used faster.

L1011 · 26-03-2021 5:50pm

McGaggs wrote: »

My parents looked into this in the 80s, on a diesel Peugeot. They drove something like Sligo to Dublin only putting in a bit of fuel at each stop, and then on the way back brimmed it. No decent roads back then, don't was a long journey. Not filling it was actually cheaper, but they decided they'd rather have a slightly higher cost than stopping more often.

That wouldn't be a valid test as the trip is not actually identical each way and definitely wasn't back then

You could be stuck in Kinnegad far longer heading East than West due to right turning drivers on to the N6, could be caught at the bridge in Carrick On Shannon more often heading East too. Trying to remember other former (and current for COS) nightmares on that route is giving me traffic jam PTSD though!

Bass Reeves · 26-03-2021 5:55pm

L1011 wrote: »

That wouldn't be a valid test as the trip is not actually identical each way and definitely wasn't back then

You could be stuck in Kinnegad far longer heading East than West due to right turning drivers on to the N6, could be caught at the bridge in Carrick On Shannon more often heading East too. Trying to remember other former (and current for COS) nightmares on that route is giving me traffic jam PTSD though!

As well more than likely Sligo to Dublin the wind effect would be positive on your journey, Dublin to Sligo would have a negative impact on your journey

maestroamado · 26-03-2021 5:58pm

I have checked?? It takes a lot longer for a tank to go from say full yo half than from half to MT.
The only logic here is the fuel at top of tank is protecting the fuel being used at bottom of tank as less air in tank so less evaporating...

The J Stands for Jay · 26-03-2021 6:04pm

L1011 wrote: »

That wouldn't be a valid test as the trip is not actually identical each way and definitely wasn't back then

You could be stuck in Kinnegad far longer heading East than West due to right turning drivers on to the N6, could be caught at the bridge in Carrick On Shannon more often heading East too. Trying to remember other former (and current for COS) nightmares on that route is giving me traffic jam PTSD though!

Totally agree it's not a valid test, but the conclusion being that stopping more often is too much hassle is the important takeaway.

PatM65 · 26-03-2021 6:12pm

maestroamado wrote: »

I have checked?? It takes a lot longer for a tank to go from say full yo half than from half to MT.
The only logic here is the fuel at top of tank is protecting the fuel being used at bottom of tank as less air in tank so less evaporating...

I would imagine much of that is down to the amount of fuel the pipe from the filler cap to the top of the tank holds. The fuel gauge won't start to move until you start to use the fuel in the tank itself.

colm_mcm · 26-03-2021 6:17pm

The shape of the fuel tank is a factor too. They’re often wider at the top.

CoBo55 · 26-03-2021 6:37pm

Bass Reeves wrote: »

You would be carrying about an extra 20 kg on average. Considering a fairly average car with two people in it weights about 2 ton, 20 kgs is less than 1%, of the gross weight.

Fuel efficiency is also effected by aerodynamics and tyre pressure as well as other factors an extra 20 kgs will use less than 0.5%extra fuel. In a car that takes 60 litres that's about 0.3L/fill if car is filled to the brim every time compared to 1/4 filling a car.

Starting a car uses fuel. The physical act of getting a car moving( think about trying to push a car it takes more energy to get the car rolling than to keep it rolling) using extra fuel as well as getting it back up through the gears to a road speed.

Finally you have evaporation. A petrol tank is a sealed tank so it holds any petroleum gas within the tank. If you ever open a gallon that holds petrol for a lawnmower or chainsaw especially in hot weather you will literally see the gas escaping. Exactly the same happens when you open a tank of a car.

Modern petrol cars don't allow petrol fumes into the atmosphere, the fumes are contained in a charcoal cannister and burned by the engine.

Larbre34 · 26-03-2021 6:40pm

Fuel is heavy. Why would you carry more of it around than absolutely necessary? All it does its increase its own consumption.

20 quid on a typical Irish diesel is good for 300-350 kms, loads.

Del2005 · 26-03-2021 7:00pm

Larbre34 wrote: »

Fuel is heavy. Why would you carry more of it around than absolutely necessary? All it does its increase its own consumption.

20 quid on a typical Irish diesel is good for 300-350 kms, loads.

I brim my car every time because I'd rather be sitting at home watching TV than standing at a fuel station watching the pump get close to 20.

Not everyone is driving crappy diesels so 20 won't get that far, 300km is about half of my 70l tank.

endacl · 26-03-2021 7:02pm

I started filling to the brim this time last year. Immediate improvements. I’d say I’m getting at least 3 months to the gallon.

Full tank vs frequent visits to petrol station

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