Subaru Fuel Consumption
As fuel prices rises across the world many motorists are finding ways to reduce fuel expenses by either avoiding unnecessary trips or ditching their cars altogether for a public transport.
In Tanzania Subaru cars have a bad reputation regarding high fuel consumption, while this is not true, it is safe to say that Subaru cars will consume fuel at the same rate as other cars at the same engine capacity. This article will review fuel rating for all Subaru models and ways to improve efficiency by looking at some of the factors which tend to increase consumption. Consumption is measured using a traffic metric i.e. how congested is the road, so we have City driving (highly congested like Dar es Salaam) or highway, less congestion and the average between the two.
Subaru Legacy: For a 2.0lt engine the average fuel consumption should be 10.5km/l, city driving: 8-9km/l, highway:12-14km/l.
Subaru Impreza: For an engine with 1.5lt average consumption is 11.5km/l, city driving should be 9-10km/l and highway 13-14km/l.
Subaru Forester with 2.0lt engine average consumption is 9.3km/l with 8-9km/l city driving and 11-14km/l highway driving.
Anything that deviate drastically from these ratings such as if your Forester is logging 5km/l for city driving should be considered a problem as explained below.
To operate at an optimum efficiency modern cars employ the use of sensors and computers to drive an engine. Subaru boxer engine like any other is a four stroke internal combustion engine using spark, pressure(boost) and air-fuel vapor to generate power. These parameters must be coordinated to ensure that ignition occur just at the right moment i.e. at correct pressure and air-fuel ratio. Air fuel ratio(Afr) is an important aspect in combustion process as it determines if the air fuel mixture is combustible at all and how much energy is released. The ultimate goal of the engine is to operate at perfect Afr where there is enough air to burn all the fuel called stoichiometric mixture or stoich. Ratio lower than stoich called 'rich' (i.e. consume more fuel) are less efficient but produce more power, and those higher are called 'lean' are more efficient but cause pollution. To calculate the Afr oxygen content of the air mixture must be measured and known. Dirty air mixture or malfunctioning sensor may throw off this measurement and may cause the computer to miscalculate the Afr causing a rich or lean burn.
Most of the Subaru imported in Tanzania are high mileage cars used from other countries such as Japan or Malaysia, with these most of the sensor are at the end of life as a typical oxygen sensor has a lifetime of 100,000km, while the sensor may be working it might be reporting incorrect values causing the Afr to go off. An aged Spark plug with wide gap or fuel soaked one can also cause high consumption due to engine misfire.
If your Subaru fuel consumption is low than 7km/l for city driving we at Fuji Heavy Garages may help you raise it as we helped others by evaluating the car current state and advice way forward to improve consumption. The initial cost to improve fuel consumption may in the long run outweigh the extra cost incurred in fuel expenses.
