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hi, i have a bmw , and it has a sunroof, is it more economical to open the sunroof for less fuel consumption, or would the window be the better option.
thanks

Hi to get lower fuel consumption I believe it is better to leave sunroof and windows closed whilst driving as it reduces the wind drag.
Another way to reduce fuel consumption is that if you are using 91 octane fuel switch to 95 octane and you will find that the engine uses less fuel, gives smoother and better performance. I did this on my 3 litre car and use approx 1 litre less per 100 kms in city use. The extra cost for 95 is well worth it.. You could also switch to 98 octane but I am not entirely convinced that the extra cost is actually worth the benefits.
Roland5

Thanks for this Roland - leads me to ask my own question, and demonstrate my complete ignorance on such things. I had heard about getting more fuel ecomony using 95 as opposed to 91 octane, but wondered how this was possible? Isn't the fuel delivery system in engines pretty much mechanically driven, so that a similar volume will be delivered to each cylinder (obviously throttle dependant). Even in 'electronic ignitions' how exactly does the system 'detect' the actual power output and adjust fuel volume accordingly? Cheers, Rich.