This was posted on the vw forum I used to frequent in my campervan days.
Useful tips:

Here at Marian Hill Pipeline where I work in Durban , we deliver about 4 million litres in a 24 hour period thru the pipeline.. One day is diesel, the next day is jet fuel, and petrol, LPR and Unleaded. We have 34 storage tanks here with a total capacity of 16,800,000 litres.


Only buy or fill up your car in the early morning when the ground temperature is still cold..


Remember that all Service Stations have their storage tanks buried beneath the ground. The colder the ground the more dense the fuel. When it gets warmer petrol expands, so buying in the afternoon or evening ........... your litre is not exactly a litre. In the petroleum business, the specific gravity and the temperature of the petrol, diesel, jet fuel, ethanol and other petroleum products play an important role. A one degree rise in temperature is a big deal in this business but the Service Stations do not have temperature compensation at the pumps.


When you are 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. In slow mode you should be pumping on low speed, thereby minimising the vapours that are created while you are pumping. All hoses at the pump have a vapour return. If you you are pumping on the fast rate, some of the liquid that goes into 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 tank is HALF FULL .


The reason for this is, the more fuel you have in you tank, the less air occupying its empty space. Petrol evaporates faster than you can imagine. Petroleum storage tanks have an internal floating roof. This roof serves as zero clearance between petrol and the atmosphere, so it minimises 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 fuel truck pumping into storage tanks when you stop to buy, DO NOT FILL UP. Most likely the petrol/diesel is being stirred up as the fuel is being delivered and you might pick up some dirt that normally settles on the bottom.


Hope this will help you get the most value for your money. Remember to always fill your car when the tank shows 'half'. Always fill up in the early morning. Always fill up in slow mode.

That's useful stuff, thanks Lyn.

Real handy, will keep that in mind

I'd take all that information with a huge pinch of salt.
Petrol tanks have floating roofs? I've seen two installed & three decommissioned & they were just tanks with baffle plates inside, basically, a larger, stronger version of the car tank (with a few extras thrown in such as earthing, additional walls etc.
Also, the temperature below ground tends to be relatively constant. My parents owned a pub with a beer cellar - the best place to work in the scorching summer & certainly quite pleasant in the winter, the beer was always chilled, whatever the weather (whereas pubs without cellars had to use chillers to cool the beer before serving).
My pond is 8 feet deep, 4 below & 4 above ground. The bottom tends to keep an even temperature throughout the year, with perhaps a 1 degree variation.
As for deliveries stirring up loads of silt in the bottom of the tank, many people still believe that of car tanks. I hear people say "I never let my tank go below 1/2 or 1/4 because it then draws all the muck through"
So as you are driving along, bouncing over road humps, around corners accellerating or stopping, the fuel is perfectly steady in the tank?
The insides of tankers are clean, the fuel will be filtered before it is tanked & I guess it might pass through a filter in the pump? But it certainly passes through a filter before going into the engine.
And I've noticed that when forecourts have deliveries, the station is closed off - certainly at the ones round here where I have noticed deliveries generally late evening/night.
I certainly doubt that the temperature as you fill the car would really make that much difference to the quantity you get. Fuel tanks in cars are designed specifically to have a vapour layer above the fuel, it is impossible to fill this with fuel. This allows for any expansion or evaporation - so no need for floating roofs.

Agree with that Sludgeguts.

Just out of interest.. I just changed the fuel filter on a 1.3 multijet, very clean element and not even one drop of water in the water trap, in 20,000 miles.

I think regular pump diesel is very clean.

I did once fill up my Kawasaki in the morning from the petrol station near work. I very carefully filled the tank right up to the brim, payed and then rode the half mile to work.
When I came out that evening the fuel tank was covered in a dirty layer where the petrol had expanded in the heat of the day and oozed out of the tank. Made a right mess.
Provided the tanks are underground though I agree with Sludgey and that it pobably won't make much of a difference. Perhaps if you live in a REALLY hot country it might, but I suppose every drop counts.

I thought when I saw the subject that it might be tips on filling the Doblo. Unlike most of you, my vehicle is the 1.2 petrol and it has the worse filler I've ever used. I've hardly ever seen the fuel gauge on full because I usually give up after the pump has shut off half a dozen times. The oil filler is even worse, any more than a trickle and you get oil pouring down the outside of the engine.

Pumps adjust the dispensed figure for fuel temperature - at least modern ones do, and they're calibrated and tested at a set temperature. There is no advantage to filling the car when cold (anymore). I've a feeling this might not be the case in South Africa hence yer man claiming that they're not calibrated like the distribution centre is, but for british standard or NSAI standard pumps - it is.

fido said:

I thought when I saw the subject that it might be tips on filling the Doblo. Unlike most of you, my vehicle is the 1.2 petrol and it has the worse filler I've ever used. I've hardly ever seen the fuel gauge on full because I usually give up after the pump has shut off half a dozen times. The oil filler is even worse, any more than a trickle and you get oil pouring down the outside of the engine.

Click to expand...

I used to have a car like that, a real PITA especially when you need to fill the tank from near empty. I thought it may have been due to the way the baffles were placed in the tank so the fuel flows into the tank faster than it can flow between baffles, that and/or the filler tube is too narrow?
I used to have to fuel up with the nozzle almost out & gently squeeze the trigger so it filled slightly slower than normal.