By Martin and Nick | Edited by Steve N Updated 7 Aug 2015
While diesel is now cheaper than petrol at some pumps for the first time in a decade, the price of both has risen since the start of the year. Yet it's possible to drive down the cost by buying in the right place in the right way.
MSE Challenge: The petrol diet!
Once you've read the steps below, why not try the petrol diet? No, we don't advocate swigging the stuff - it's a challenge on the MSE Forum, where MoneySavers share tips to help cut their annual fuel spend, track savings, and inspire others.
The forum's proved hugely powerful in the past, seeing people work together to get debt-free, pay off mortgages and more. It's free to join, and open to all - see the Petrol Diet discussion .
Step 1: Make your car more fuel-efficient
Keep your tyres inflated Fuel efficiency improvement: Up to 3%
Lower tyre pressure increases the drag on a car, meaning you need more fuel, so regularly check the pressures are correct and your car needs less oomph to keep it moving.
Declutter your car Fuel efficiency improvement: Up to 2%
The lighter your car is, the less effort it needs to accelerate. By decluttering, clearing out junk from the boot, and not carrying unnecessary weight, you can save more. On average, every extra 50kg you ride around with ups your petrol by 2% - and this could be even more in smaller cars.
Take your roof rack off Fuel efficiency improvement: Up to 10%
A roof rack, even unused, adds wind resistance to a car, increasing drag and making the engine work harder. The RAC estimates a roof rack can affect fuel consumption by a whopping 10%. If you don't need it, take it off, along with anything else inefficient. Even closing the windows will make the car run slightly more efficiently.
Turn off air con at lower speeds Fuel efficiency improvement: Up to 10%
Newer cars are getting better on this, but air conditioning still uses an incredible amount of fuel - so make sure it's turned off unless you really need it.
The general consensus is it's more efficient to drive with the windows down and the air con off at lower speeds, but at higher speeds it's better to use the air con and keep windows up due to the extra drag caused by having windows down. At motorway speeds air con can affect fuel consumption by about 3 to 4%, whereas it can be up to 10% in stop and start traffic.
If you're not using your air con, it's worth turning it on once in a while as not using it can mean it stops working. Also, don't keep the engine running. Drive off as soon as you start up and switch off the engine as soon as you reach your destination. Turn your engine off where possible, eg, in traffic or during big delays on motorways.
Don't fill it up Fuel efficiency improvement: Up to 1%
Fuel is heavy, so by filling the car up you're adding quite a weight. The less fuel your car has in it, the more efficiently it drives. If you fill up slightly more often and put less in (to 1/2 or 3/4 full), it'll make the car run more efficiently.
But don't be tempted to run the fuel too low - winter driving uses more fuel, so you'll cover fewer miles per litre.
Step 2: Seven tips to drive more efficiently
You can drive the same distance in the same car, without slowing down, but using far less fuel. This is the biggest single factor effecting your fuel costs, and in some cases people find they save 30% when they change driving habits. The key is to drive smoothly. Here are the seven tips you need to know.
The accelerator is a money pump - accelerate gradually without over-revving. Speed up smoothly. If you press harder on the pedal, more fuel will flow - but you can reach the same speed using much less power. As a rough rule, stay under 3,000 revs. Plus, if you think about it, if you accelerate too quickly, chances are you'll then have to brake hard, which isn't
Change up a gear sooner. Always drive in the highest gear possible without labouring the engine. So change up much earlier than feels natural – it will take some pace out of your acceleration, but as that’s our first tip it isn’t a bad thing. If you have a fuel efficiency display, you’ll be surprised how immediate an impact this has.
Think about road position. All the other tips require you to be alert and aware of your road position. This helps you plan ahead and move gradually. It also means that more efficient driving is also safer driving.
The brake is a money burner. Where safe, allow yourself to slow naturally When you press the brake you are effectively converting the energy you’ve paid to put into the car into heat. Instead if you can slow naturally you’re using all the stored energy most efficiently. Good road positioning is crucial for this.
Listen to the noise of your engine. If you hear sharp acceleration and the screech of the brakes you know you’re doing it wrong. Imagine driving from traffic light to traffic light doing that. The person behind who speeds up and slows down more slowly will still be behind you at the next light, they’ll just have spent far less getting there.Keep moving if you can. The most expensive metre you drive is always the first one when you start. It takes huge energy to get a car going. So if you can roll gradually up to a traffic light as it changes from red to green, without stopping, it is more efficient than stopping and restarting
Coasting in neutral may feel cheaper but it's dangerous. While putting the car into neutral and coasting may feel like you’re using less fuel, it's dangerous, don’t do it. You always need access to the accelerator to avoid unexpected hazards. Plus cars can handle far worse on sharp corners when in neutral.
In many ways, this all comes down to one little rule of thumb.
Every time you put your foot on the accelerator, remember the harder you press, the more fuel you spend.
Just being conscious of this, and your road position, should massively increase how far you can drive on a tank of petrol. It's estimated someone who averages 35 miles per gallon could reach 40mpg by driving better, a near-15% saving.
The real world impact: Martin's story
On an overseas holiday I got to test this, thanks to a sexy little digital display in my hire car which gave me a km/litre readout. For every trip, I drove normally on the way there and used the "think when pressing the pedal" method above on the way back.
If you're thinking "did he really bother while on holiday?" - yes I did, and I loved it. Luckily my girlfriend (now my wife) is very understanding!
The improvement is enormous!
Overall, I drove about 500 miles, and the different 'efficiency' averages per litre of petrol were incredible: for normal driving, it was 11.2 kilometres per litre, but for efficiency-conscious driving, a remarkable 13.4 kilometres per litre.
Most intriguingly, the efficient driving didn't cost me any time at all, and on motorways my top speed didn't change. Others drove harder, only to brake harder at the next traffic light.
MSE founder & editor
For someone spending roughly Ј50 a week on fuel, an equivalent 20% efficiency increase would save around Ј500 a year. And, according to the RAC, boy racers could expect annual efficient driving gains of up to 30%!
For more info on this read Martin's blog: Petrol Efficiency Experiment. If you try this type of driving or want to share your experiences, go to the Driving Efficiently forum discussion.
Step 3: Find the cheapest petrol or diesel prices
The easiest way to find the cheapest forecourt in your area for petrol, diesel, LPG and more, is by comparing prices at free website PetrolPrices.com .
After registering, enter your postcode and tell it how far you're willing to travel (2, 5, 10, 15 or 20 miles) and it'll list today's cheapest petrol stations in your area for unleaded, diesel, LPG and other fuels. A quick check before you need to fill up should be enough to save you serious cash.