It may come as a surprise but even the latest and most efficient engines only manage to convert about 30% of the energy in a gallon of fuel into useful power. The rest is lost in heat, vibration, overcoming the air resistance and the drag of the tyres.
Think about it, for every three gallons you pay for you’re only getting one of them to drive you on your journey!
Taking average petrol and diesel prices at £1.20 per litre or £5.40 per gallon (and of that 65 per cent, or £3.50, is tax) and a typical car fuel tank holds say, 10 gallons, that is more than £50 of which about £30 is effectively thrown away.
Let’s start with the driving and the golden rule is to remember that nothing drinks fuel faster than accelerating so do less of it and you can achieve this by looking and planning ahead.
Let’s take a couple of everyday scenarios.
For example, if you are pulling away from traffic lights or a junction but can see slower traffic ahead there is absolutely no point accelerating hard only to have to then ease off the accelerator a few moments later.
`Ease and squeeze’ the right pedal and you will reach the vehicles ahead only a few moments later but will have saved quite a bit of fuel in the process.
Or how about a roundabout? Look further ahead as you approach and if you can see nothing coming from the right or from the opposite direction which may turn right across your path, you may not need to slow down quite so much only to then demand more power getting back up to speed.
When traffic or pedestrian crossing lights have been on red for a while as you approach it makes sense to drive more gently and try to get to them as they go green without having to stop.
Always think about the momentum in the car. You’ve burnt fuel building it up so there is no point in wasting it by stopping and then having to start all over again.
Remember, that gauge on the left of your dashboard, with RPM written on the bottom, shows how many times the pistons are going up and down per minute and the higher the figure the faster the engine is drinking fuel.
By the same token, don’t hold onto the lower gears for so long before changing up to the next one.
Modern engines are good at producing what is called torque which you need to accelerate or go up a hill and this tends to come at lower to mid-revs. For a diesel you’ll need no more than 2,000 rpm in normal driving, perhaps 2,500 for a petrol car.
Coasting, knocking the car into neutral if you’re going down a hill? It’s frowned upon to say the least because, in theory, you have less control. Perhaps a better reason is that these days the engine management computer tends to cut the fuel supply when you take your foot off the accelerator anyway so there is little to be gained.
Keep to the speed limits. It’s obvious from a legal point of view but also in terms of fuel saving; an average hatchback burns about 9% more fuel at 70mph than at 60mph and up to 15% more than at 50. Because the air resistance builds with speed, you will use about 25% more fuel at 80 mph than at 70.
So, to sum up the do’s and don’ts from behind the wheel:
• Do look ahead and plan ahead.
•Do ease and squeeze the accelerator.
•Do change to a higher gear at lower revs.
•Do try to keep rolling in slow traffic if possible rather than stopping and starting.
•Don’t speed up to the back of a queue when there is no point.
•Don’t lose speed needlessly only to then burn fuel regaining it.
There are some easy and obvious things you can do to the car itself to save fuel too.
Do’s and don’ts.
• Do remove any unnecessary weight.
•Do keep the tyres at the right pressure.
•Do keep the engine serviced.
•Don’t waste fuel letting the car warm up before driving.
So, to the big question –
how much will you save?
A professional, highly experienced driver could see a gain of at least ten per cent just by following these tips. The less efficient driver will see an even bigger benefit. There is an annual MPG Marathon taking in hundreds of miles over a variety of roads and the winners usually see improvements of this order over the official fuel consumption data.
Something to think about the next time you fill up and ponder that for every three gallons you pump in two of them are effectively being wasted.