Quote:
Originally Posted by nu11eaf
If only that were true. Larger engines mpg % would/may not drop as much as they would not have to work as hard.
It obviously also depends on the weight you are towing, my caravan is 1500kg, plus everything including the kitchen sink.
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If you use the power it will drink the fuel. Specific fuel consumption doesn't vary much with the engine's swept volume. It doesn't matter much whether the engine is big or small to produce a certain level of power utilised, it will use the same fuel if of the same family of engines. If the bigger engine is substantially more powerful but driven behind a four cylinder, therefore driven no harder, both should use about the same fuel with a theoretical advantage to the smaller volume engine due to lesser friction and pumping losses and a lower mass.
It should be remembered that due to a combination of engine and transmission efficiency improvements, todays vehicles are far more efficient than older ones. For instance I had a factory diesel 2.4 litre four cylinder manual Range Rover, many years ago, that output a heady [for the day] 112hp at 4400rpm but absolutely nothing under 2200. There's one steep hill locally that required me to rev to the governor in first in order to keep the engine above 2200 so that second gear could be sustained without having to immediately change back to first. It was a terribly noisy engine and when towing my caravan up moderate but long hills, a close watch was needed on the temperature gauge. It served me reliably for nearly 100,000 miles.
Fuel consumption never bettered 26mpg though. Even though it was a good bit smaller and lighter than the Volvo and had a manual gearbox and considering that the Volvo has nearly twice the horses and three times the torque and can run rings around it in performance terms. I get 38mpg on average from the Volvo.
Towing is a great leveller. I suspect that if a 2000kg caravan was towed at normal A-road speeds in traffic, there would be little difference in consumption between D4, D5, V60, V90 or XC90. They would all actually use the same amount of power and therefore near enough the same fuel for that job. Some would have more power in reserve but power not used is power not produced and not fuelled for.