Petrol myths, busted

Black car without number plates parked at petrol station

Sue Hewitt

Posted July 17, 2019

RACV experts debunk 10 of the most common petrol myths.

So we all know it’s cheaper to buy petrol on a Tuesday, right? Wrong. 

The cheaper-on-a-Tuesday myth is just one of the common misconceptions many of us have about petrol – along with manual cars being more economical to drive and the dangers of using your mobile phone while filling up at the pump. And with petrol prices peaking at near-record highs in recent months, it’s never been more important to separate myth from fact.

We asked RACV’s manager of vehicle engineering Michael Case to debunk 10 of the most common myths about petrol. 

Top 10 fuel myths


Tuesday is the cheapest day to fill up

Michael says the days of predicting the cheapest petrol day are gone. He says no one can predict the peak-to-low petrol price cycle and which day fuel will be the cheapest. (You can, however, use RACV's fuel price monitor to help find the cheapest petrol near you.) 

In the past, the price cycle was exactly a week long and everyone discovered “cheap Tuesdays”. But since 2013, the price cycle has varied from nine to 42 days.  

The cycle is driven by retailers undercutting their competitors to get a larger market share. Michael says that on the downward trend retailers discount petrol by one to two cents a litre until one retailer breaks rank and ups the price. The price at the pump can suddenly soar by up to 40 cents a litre. 

Running on almost empty can ruin your engine 

Not true, says Michael. In a modern car petrol is pumped from the lowest point in the fuel tank, so whether it is full or empty makes no difference because the petrol is pumped from the same point.  

You can blow up a petrol station by using your mobile phone 

There are no documented incidents where a mobile phone has caused a fire or explosion at a petrol station. Michael is unsure how the myth started but says scientific evidence does not support the hypothesis. 

Country petrol prices are always higher than in the city  

With fewer petrol retailers in regional areas, competition is often quite low so there’s little incentive to lower prices. While this leads to long periods of relatively steady prices, regional prices do drop below Melbourne prices. There are times when Melbourne’s price peaks are substantially higher than regional prices. Michael advises regional drivers coming to Melbourne to check city prices to see if it’s cheaper to fill up at home.  

Fuel prices always hike up before a long weekend   

Despite what motorists imagine, petrol giants do not deliberately increase prices just because you are heading off for the long weekend. Michael says it has to do with the petrol price cycle, driven by retail competition. Retailers discount prices to attract customers in a competitive market but as those prices approach wholesale costs, retailers raise prices, which can drive a sharp spike, before the discounting phase begins again. That cycle might be in a discounting phase ahead of a holiday, resulting in lower prices. He says, for example, drivers may have noticed there was a petrol price spike just before the July school holidays and about a week before the Queen’s Birthday long weekend, however there was no price rise at Easter or last Christmas. 

Premium petrol is better for your car

Some new vehicles require the premium 95 or 98 RON unleaded petrol, but older vehicles may not get any benefit from this pricier fuel. Some newer cars may get increased efficiency and performance but not likely enough to compensate for the higher price.

Retailers never sell below the wholesale price of petrol 

Petrol stations do sell below wholesale prices to match or beat their competition. Often the super-low price lasts only a short time. Michael says retailers will sometimes sell below wholesale price because they can offset the loss by motorists shopping in the service station store or by attracting shoppers to spend a certain amount in partner supermarkets.

Motorists can’t influence petrol prices 

Drivers who shop around put pressure on retailers who want to keep customers. Michael says competition triggers the slow discounting cycle where retailers reduce the price by one to two cents a day until they get to or below the wholesale price and the price spikes upward.

Manual cars are more economical than automatics 

That used to be the case, but no longer is. When automatic transmissions were quite basic they typically increased fuel consumption and reduced performance. Michael says modern automatic transmissions can match or better a manual’s economics.

E10 fuel is cheapest

RACV vehicle testers drove from Melbourne to Albury and back and confirmed motorists get less mileage using E10. Michael says E10 has a lower energy content and therefore increases fuel consumption by about three per cent. So unless you are paying three per cent less for E10 than for unleaded petrol, it’s a false economy.