On a test-drive almost any car can give you anything from five kmpl to 25 kmpl depending on how it is driven, the roads and the traffic conditions. But in addition to getting a fuel-efficient car you need to become fuel-efficient too. Here are some of the main fuel consumption killers:
Cold engines: It takes about 10 minutes for your engine to warm up to achieve thermal efficiency and your fuel consumption may go up by up to 50 per cent. So if you have to do short trips do not expect good fuel consumption.
Driving at high engine speeds: If you like to rev up your engine you will get the thrill of fast driving but will have to pay a price for it. Conversely if you keep the engine at minimum speeds your fuel consumption will be very much better but driving in too low speeds will also cause knocking and shorten engine life. The main reason diesel engines consume less fuel is because they deliver good torque at low engine speeds so you can drive in higher gears.
Too many stops and starts: Driving in traffic with periods of idling at red lights or when stuck at traffic is a fuel consumption killer. If you spend 10 minutes idling on a 30-minute trip, your fuel consumption may double.
Bad roads: These can combine the impact of too many stops with the need to use high engine speeds in low gears to get moving, so it can play havoc with your fuel consumption.
The weight of the car: All modern engines are quite fuel-efficient but the fuel consumption is mainly affected by the weight of the car. A 600 kg Maruti 800 weighs half as much as a Civic or Corolla that will therefore need about double the fuel. Modern cars must meet current crash safety requirements and are also heavier than earlier models. But this is a small price to pay for safety.
The load that you carry: This weight factor is naturally increased if your car is overloaded with six people and loads of luggage. If you carry baggage on a roof rack then you will also experience impact air resistance.
Long idle periods: If your car is standing in the sun for a few days, there will be considerable evaporation losses.
Engine tuning and timing: Most modern engines with MPFI and other electronic engine management systems do not need tuning unlike the old carburetors but the nozzles and injectors do need to be cleaned.
Air, oil and fuel filters: Choked filters can play havoc with fuel consumption so ensure that these are regularly serviced and changed when they are dirty or clogged.
The fuel consumption figures under test conditions assume nearly perfect conditions on a flat one km run at constant speed, temperature, etc. In the real world, the figures may be out by 25 per cent or more. These factors apply to every car, bike, truck or bus and if you understand the causes of high fuel consumption you can make your vehicle much more fuel-efficient.
The writer is an automobile expert and the former editor of a national auto magazine