Dan McCoey | Jun 16, 2008

By Daniel McCoey

With the price of regular unleaded topping $1.60 in Australia this week, protests breaking out across Europe at the price of fuel and an emergency oil summit being organized by a bunch of disgruntled nations, it seemed appropriate to look at ways you can stretch your fuel dollar further. Of course you could buy a hybrid but for us enthusiasts that would be a little like giving up on life, so lets look at how you might save a few dollars.

The first tip when refueling is to make sure you do it only in the dead of morning when it’s still cold, the colder the outside temperature the better. Most service stations have their storage tanks underground and the temperature of the fuel you buy will make a difference. The colder the ground, the colder the tank. The colder the tank the denser the fuel. Liquids expand as they warm and it is no different with petrol and diesel. A litre of fuel bought in the cool of the morning is denser than a litre of the same fuel purchased in the warmer afternoon. Simply put, filling up early in the morning means you are getting the best bang for your bowser buck.

Oil companies know all about the effect of temperature on fuel. When supplying their retailers they take into consideration the specific gravity and temperature of the fuel held in bulk storage to ensure that they supply their retailers with a real litre of fuel. They do not employ the same tactics at the pump though, where there is no temperature compensation and a litre is not necessarily a litre.

gas-pump

Another tip when filling up is – don’t rush. Most bowsers have the ability to ‘click in’ to a high flow rate but that doesn’t mean you have to use it. If you have the time then slowing down the fill rate minimizes the vapors that are created from the fuel being pumped. All hoses at the bowser have a vapour return for safety and those vapours are not returned to your tank despite the fact that you are about to pay for them. It’s a little like opening a bottle of Coke and pouring a glass quickly, you end up having to wait for the gas and bubbles to subside before you can return to filling your glass. Filling your tank quickly results a similar build up of vapour that either heads for the atmosphere (you can usually see the vapour itself distorting and refracting light around the filler) or returns to the storage tank via the vapour return.

It is common knowledge now that there are fuel price cycles each week and it pays to watch when Petrol stations in your area raise and lower their prices. Generally the best days to buy are at the start of the week with prices generally being bumped up from mid week onwards and then slowly working their way down again by the end of the weekend.

Fuel loss through evaporation can also be reduced by constantly keeping your cars fuel tank at least half full, although it may not be terribly convenient at times. Not only do Petroleum companies monitor and regulate the temperature of their fuel supplies, they also monitor the specific gravity of the fuel being held in storage tanks. Their storage tanks are equipped with an internal ‘floating roof’ that ensures there is zero clearance between the fuel and the atmosphere minimizing evaporation losses through exposure to the atmosphere. Maintaining half a tank of fuel in your car acts in a similar way to the storage tanks ‘floating roof’.

If Oil companies have processes in place to reduce losses from temperature differences and evaporation then you can bet there is a significant dollar it. It also means that there is potential for you to ensure that each dollar spent at the bowser buys you a full dollars worth of fuel.

Using some or all of these tactics will save you some money in the long-run, it won’t be enough for a down-payment on that silver GT3 you’ve been admiring but when fuel hits $2.00 a litre (as is being predicted) a few bucks saved at the bowser has to be a good thing.

Happy and safe motoring.

[Old bowser image source: Jalopnik]