Tips on buying petrol......

Dav the wheel nut

Veteran
 Somerset
Can anyone comment on the accuracy of the following advice.

Only buy or fill up your car or truck in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the petrol, when it gets warmer petrol expands, so buying in the afternoon or in the evening....your litre is not exactly a litre. In the petroleum business, the specific gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum products plays an important role.


A 1-degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.


When you're filling up do not squeeze the trigger of the nozzle to a fast mode If you look you will see that the trigger has three (3) stages: low, middle, and high. You should be pumping on low mode, thereby minimizing the vapours that are created while you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast rate, some of the liquid that goes to your tank becomes vapour. Those vapours are being sucked up and back into the underground storage tank so you're getting less worth for your money.


One of the most important tips is to fill up when your Petrol tank is HALF FULL. The reason for this is the more Petrol you have in your tank the less air occupying its empty space. petrol evaporates faster than you can imagine. petrol storage tanks have an internal floating roof. This roof serves as zero clearance between the Petrol and the atmosphere, so it minimizes the evaporation. Unlike service stations, here where I work, every truck that we load is temperature compensated so that every litre is actually the exact amount.


Another reminder, if there is a petrol truck pumping into the storage tanks when you stop to buy Petrol, DO NOT fill up; most likely the petrol is being stirred up as the Petrol is being delivered, and you might pick up some of the dirt that normally settles on the bottom.
 
iirc when Clarkson did his London to Edinburgh and back in an Audi he mentioned filling up on a morning thing.
 
Redzedfour said:
iirc when Clarkson did his London to Edinburgh and back in an Audi he mentioned filling up on a morning thing.

I remember this. He said it was best to fill up when cold. I often fill up late at night when leaving work :thumbsup:


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Okay, what is written is accurate to a point, the only thing that I would take with a pinch of salt is the, filling up in the morning bit. Fuel is stored below ground and thus the temperature remains fairly constant, as for the rest, well all liquids evaporate and condense, and that process occurs within your fuel tank.
 
Dav the wheel nut said:
One of the most important tips is to fill up when your Petrol tank is HALF FULL. The reason for this is the more Petrol you have in your tank the less air occupying its empty space. petrol evaporates faster than you can imagine. petrol storage tanks have an internal floating roof. This roof serves as zero clearance between the Petrol and the atmosphere, so it minimizes the evaporation. Unlike service stations, here where I work, every truck that we load is temperature compensated so that every litre is actually the exact amount.

Hard to do with an ///M as the tank empties so bloody fast, would have to stop at nearly every petrol station.
 
I think the quantities you would save are pretty negligible tbh. I could understand if you travelled alot of miles in a year as it all adds up but for me it would be a couple of pence a fill up if that, il just carry on the way i do :P Interesting points though!
 
sars said:
Okay, what is written is accurate to a point, the only thing that I would take with a pinch of salt is the, filling up in the morning bit. Fuel is stored below ground and thus the temperature remains fairly constant, as for the rest, well all liquids evaporate and condense, and that process occurs within your fuel tank.

Agreed.

In reality all a bunch of nonsense and detouring 1/2 mile to fill up would make 10x the difference from a cost perspective.
 
sars said:
Okay, what is written is accurate to a point, the only thing that I would take with a pinch of salt is the, filling up in the morning bit. Fuel is stored below ground and thus the temperature remains fairly constant, as for the rest, well all liquids evaporate and condense, and that process occurs within your fuel tank.

unlikely to be an issue unless you live in an area with permafrost.............Somerset is not renown for that condition :)
 
Surely if you fill up at half a tank you're carrying around extra weight causing your mpg to drop and more fuel usage?

I always try to stay between a quarter and a half or a quarter and three quarters to avoid the gunk at the low level and to avoid too much weight at the top?
 
bluestreak56 said:
Surely if you fill up at half a tank you're carrying around extra weight causing your mpg and more fuel usage?

I always try to stay between a quarter and a half or a quarter and three quarters to avoid the gunk at the low level and to avoid too much weight at the top?

Exactly. That's what I thought when reading the article.
 
alright guys dont shoot the fella for sharing his ideas, yes may be negligible but no harm in him letting us know!
 
i think the best time to fill up is when you need petrol, if thats morning, afternoon or evening is irrelevant
 
paddy wright said:
alright guys dont shoot the fella for sharing his ideas, yes may be negligible but no harm in him letting us know!

But the opening question was asking for comment on the accuracy of the advice and that's what's come back..

Fact that most people believe it to be irrelevant in real terms answers the question.
 
I try to fill up whenever I see a good deal, regardless of how much fuel is left in the tank. Figure it brings my average pay out down a few sheets over the course of time.
 
I tend to fill up early in the morning just because there are less cars/queues in the petrol station.
 
Probably mentioned but filling at the half way point means your always carrying excess weight which affects good fuel economy
 
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