Five fuel saving myths busted

Cash-strapped motorists faced yet another fuel increase of 67c a litre while the price of diesel rose by 44c a litre.

Vishal Premlall, director of the South African Petroleum Retail Association (SAPRA), puts five fuel-saving myths to bed:

• 1. Gearing into neutral at stops

This idea may have been relevant when engines used carburettors but today’s cars have computerised fuel-injection systems. By constantly shifting in and out of neutral the only thing you may accomplish is premature wear on your gearbox.

• 2. 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.

• 3. 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.

• 4. Filling up when it’s cooler saves me money

Filling stations’ petrol is almost always pumped from storage tanks underground that are naturally insulated from large temperature swings so there is no truth in this theory.

• 5. 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.