Our mechanical engineer is here to help the average motorist in Singapore with his series of thematic Q&A articles.
THIS issue’s question-and-answer article in our ongoing Torque Shop series is about turbo petrol engines. Most turbochargers used to be found under the bonnets of high-performance cars, from Euro rockets to Evos, but these days, everything from humble little runabouts to rumbling V8 monsters can have a turbo in the engine room.
I drive a turbocharged European car. Can I fill it up with 92-octane fuel?
This is an important piece of information which you must extract from the owner’s manual.
The minimum octane rating requirement is also usually printed on a sticker on the inside of the fuel filler flap.
In general, most turbocharged engines, whether European or otherwise, require at least 95-octane fuel.
Using a lower octane rating than is recommended will reduce both performance and efficiency. However, using a higher than minimum octane rating will not have any adverse effect.
I drive a Nissan Qashqai 1.2 Turbo. Is it necessary to let the engine idle for several minutes before switching the ignition off ?
Turbocharged engines do need to cool down before they are turned off.
But in nearly all driving conditions, the engine does not reach temperatures that require a deliberate cooling-down period.
However, if you take your Qashqai to a racetrack and drive hard for two or three laps, you should give it another lap at a moderate pace, followed by a period of idling, to restore normal engine oil temperature.
Switching off when the engine is very hot stops the circulation of oil. The layer of oil around the turbocharger bearings stops flowing and literally gets “burnt”.
The black sludge that forms is similar to what you find on a burnt frying pan. That is not good for any engine.
In all other situations, even sustained high-speed cruising on Malaysian highways, there is inevitably a period of low-speed driving before parking the car or switching off the engine.
That is sufficient for the engine oil to cool to a level that will not damage the turbocharger bearings.
Also, always ensure that you are using the recommended grade and viscosity of engine oil for your turbocharged car.
At my turbo saloon’s last routine servicing, the workshop replaced the air filter. Is the replacement really necessary?
As its name indicates, the air filter in the engine compartment serves to filter the air that is drawn into the engine.
It is important that air entering the combustion chambers is clean, not only to maximise the oxygen content, but also to prevent any abrasive infiltration that could have an impact on the cylinder walls.
There are plenty of minute airborne particles and soot in the air, and the filter stops these foreign particles from entering the intake manifold and hence the combustion chambers.
Over time, the filter gets choked, and while it may continue to stop dust flowing in, the spaces that allow clean air to enter will become restricted.
A dirty air filter can cause loss of power and an increase in fuel consumption.
Air filters are relatively inexpensive (usually costing less than $200) and it would be advisable to replace them at least every 25,000 kilometres.
You could also clean the filter with a vacuum cleaner. If your air filter is the washable type, you can wash it with an air-filter detergent that you can buy from accessory shops.
Most original air filters are not washable, but there are washable replacement filters which cost a little more.
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