Bust fuel-efficiency myths

Large painted arrows on a freeway contrast with the bitumen

Les Mc Master, chairman of the Motor Industry Workshop Association (MIWA), said there are many fuel-efficiency myths doing the rounds in South Africa currently, especially following the recent truck and taxi accidents that have made headlines.

“The fact is that many fuel-efficiency tips may have worked in the past where vehicles had less sophisticated components. Most of these don’t apply anymore

since vehicles manufactured today have computer-controlled automotive systems. Some of the tips didn’t even make that much sense in the past, so as a vehicle owner you need to be savvy about the tips you receive and rather ask an expert if in doubt,” said Mc Master.

Based on tips from MSN Autos, Mc Master offered his advice on these fuel-efficiency myth busters:


Gearing into Neutral at stops


THIS myth may have been relevant when engines used carburettors, but today’s cars have computerised fuel-injection systems. These systems sense if an

engine is revving above idle when you ease off the accelerator. If that happens, the fuel injectors shut off, so fuel is no longer injected into the engine, even if the car is still in gear. By constantly shifting in and out of neutral, the only thing you may accomplish is premature wear on your gear box.


A full tank is more fuel efficient


THE idea that a tank more full than empty will prevent fuel evaporation inside the tank is incorrect. Fuel systems in modern cars are designed with vapour

recovery systems so no evaporation is possible. Some vehicles with pressurised fuel systems even display a ‘check engine’ light if the petrol cap is loose, missing or not properly sealed.


A dirty air filter leads to lower mileage


THE engines in older vehicles pulled air straight through the air filter into the carburettor, so a clogged filter could affect fuel efficiency to some degree. However

today’s advanced engines have a computerised engine control module (ECM) to regulate the air-to-fuel ratio. Air goes through the filter and then through a mass airflow sensor that lets the ECM gauge the airflow and adjust the fuel accordingly; less airflow means less fuel is sent to the engine. While fuel efficiency may not be affected, dirty air filters can lead to sluggish acceleration.


Filling up when it’s cooler saves me money


FOR years, a myth has been circulating that if you buy petrol during the cooler part of the day you get more for your money, since a cooler liquid is denser. This theory may sound believable but at filling stations petrol is almost always pumped from storage tanks underground that are naturally insulated from large temperature swings. Because of this, any slight change in the temperature of the petrol is so small you wouldn’t notice any real savings.


Cruising downhill in Neutral saves petrol


THIS is one of the biggest myths thrown around. The truth is that when coasting in Neutral, the engine is idling, consuming just as much petrol as when it’s idling at a traffic light or warming up in your driveway. The reality is that it’s actually a bad idea to roll downhill or up to a stop sign in Neutral because you need

to be able to use the accelerator to avoid an unexpected road hazard. Cars don’t handle well in Neutral during sharp cornering manoeuvres when the engine isn’t connected to the drivetrain – the components in the vehicle that generate power.


Fuel saving devices


LASTLY, be aware of claims made by manufacturers regarding fuel saving devices. There are a number of different devices doing the rounds and each one is purported to have magical fuel saving powers, be it a magnet device connected to the fuel supply line which “aligns” the atoms in the fuel by electromagnetic field, to the swirl or vortex device which is fitted to the intake manifold. There is no scientific evidence that any of these devices will in any way improve the fuel efficiency of a motor vehicle. Be cautious of marketing ploys and before you consider purchasing such a device, seek the expertise of your nearest MIWA dealer to guide your decision making. Rule of thumb, if it sounds too good to be true, it probably is! Many a gullible consumer has been duped into doing costly damage to their vehicle by the unscrupulous marketers of these devices.

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