Savings on Fuel - Part Three

In the first and second part of this series we looked at choosing the most economical car for your needs and maintenance steps to further aid economy. See Savings on Fuel – Part One and Savings on Fuel – Part Two

Now we’ll check out driving techniques that you can adopt to reduce your fuel bill.

Drive Smoothly

Watching the road ahead is one of the key aspects of driving smoothly.

By watching the road a generous distance ahead you have more time to react to changing traffic conditions such as traffic lights. This means you can ease off the accelerator early, coast toward the lights and gently apply the brake to wipe off the remaining vehicle momentum. This is by far the most fuel-efficient way to drive.

In addition to watching the road ahead, it’s important to maintain a generous distance to the car in front. All too often, drivers follow too closely, which causes them to drive with on/off movements of the accelerator and so use excess fuel. If you watch the road ahead and leave a considerable distance to the car in front, you can identify any lane obstructions and have plenty of time to merge into another lane with the flow of traffic. This technique means you’ll avoid getting stuck behind buses, turning vehicles and collisions.

Accelerate with the smallest possible amount of throttle and ensure throttle application is gradual. You should also begin feathering the throttle well before you arrive at your desired speed – if you lift off when you arrive at your desired speed you’re wasting fuel.

On the open road you should use the car’s cruise control (where fitted) to ensure steady speed and fuel consumption. However, cruise control does not necessarily give optimal fuel consumption in hilly terrain. A more economical approach is to maintain constant throttle position and allow some variation of road speed.

Fuel consumption increases rapidly at road speeds over about 100 km/h. Cruising at 90 km/h delivers significantly better fuel consumption than cruising at 100 km/h – just make sure you don’t hog the fast lane...

Use Low Engine Revs

Fuel consumption increases as a function of engine speed (rpm).

If you drive a car with a manual gearbox you can change up through the gears at relatively low revs. The revs at which you should up-shift varies from vehicle to vehicle but, as a rule, you should not need to exceed an engine speed that’s half the redline. For example, if you’re driving a car with a 7000 rpm redline you should avoid exceeding 3500 rpm. (But note that engines with poor low-speed torque may require higher revs.)

If you drive a car with an automatic transmission, you can encourage low rpm up-changes by gentle, smooth application of the throttle. Experiment with different throttle positions and rates of throttle application to find the driving style that causes the transmission to change up gears as early as possible.

Reduce Idle Time

The longer your car’s engine idles, the more fuel you waste.

Prolonged idling in traffic is responsible for a considerable amount of city fuel consumption. Wherever safely possible, you should switch off the engine to halt unnecessary fuel consumption. Starting and stopping the engine increases engine wear, but the effect is negligible once the engine is up to normal operating temperature.

The practice of ‘warming up the engine’ before driving wastes fuel. A more fuel-efficient alternative is to drive the car gently (at light throttle and low revs) for the first few kilometres.

Many owners of turbocharged cars are guilty of wasting fuel during unnecessarily long idle-down periods. Vehicle manufacturers typically fit an in-cabin warning sticker that suggests a specific idle-down period – for example, a Mitsubishi Galant VR4 has a sticker that suggests idling the engine for 60 seconds immediately after operating at high speed or under heavy load. This is ample time to cool down. Idle time can be significantly reduced by driving conservatively for a minute or two before stopping. If you drive conservatively well before stopping, you can safely reduce your idle time to a handful of seconds. That’s the best way to do it.

Putting these Techniques to the Test To demonstrate the benefit of these driving techniques, we did a back-to-back fuel consumption test in a 1.8 litre turbo Nissan 180SX automatic. The test resembled the official UN ECE R101 test procedure with about 30 percent open-road driving and the remaining 70 percent a mixture of urban and city driving. The engine was switched off and started 3 times during the test. Each of our 200km test loops began with a cold engine and with near-identical weather and traffic conditions. The first test was done with a ‘normal’ driving style – not looking a long way ahead, jerky acceleration and braking and with a one minute idle-down for each switch-off. The result of this test was an average fuel consumption of 9.75 litres per 100km. The second test was done with a smooth driving style and a 20 second idle-down for each switch-off. The result? An average consumption of 9.0 litres per 100km – an improvement of 8 percent. Not a bad saving for simply using a bit of nous...

Minimise Use of Air Conditioning

Car air conditioning systems cause a noticeable increase in fuel consumption.

In slow moving traffic, an air conditioner keeps vehicle occupants much cooler than winding down the windows. It would be silly to suggest not using the air conditioning, but you can make a fuel saving by occasionally switching it off or setting the cabin temperature somewhere above ‘Max Cold’.

At a higher road speed it’s not clear-cut whether it’s more fuel efficient to use the air conditioning or wind down the windows. We have seen conflicting information on what’s the most efficient approach. We imagine results will vary depending on vehicle aerodynamics, the power consumption of the air compressor and many other variables. Why not perform your own testing as part of your daily driving?

Smart Vehicle Usage

You can save a very significant amount of money just by planning your vehicle use.

If you have a number of appointments and errands for the day, it’s best to schedule them in one trip rather than several trips. Don’t be caught in the situation where you need to drive to the local shops because you forgot to buy a drink...

Also consider the time of your trip. Wherever possible, try to avoid peak-hour traffic and major social events. Heavy traffic conditions are killers for fuel economy.

In Part Four – the final - of this series we’ll take a look at aftermarket vehicle modifications that enhance fuel economy...