Say you have a small 4 cylinder manual transmission car. To simplify stuff, we'll assume you are on a relatively straight highway with no traffic and no stops or intersections.

Question: Which is more fuel efficient, constant driving at, say 40 miles per hour versus cycles of moderate acceleration to 40 mph + x mph then coasting with the engine idling and gear in neutral until speed is 40 - x mph then re accelerating. X = 10 or 15 mph.

A regular tune-up will not only keep your engine sounding the way it should, it’ll perform the way it should. A benefit of this is keeping the car’s fuel consumption as low as possible.There’s no need to pay for anything fancy here; in fact, cleaning or replacing the air filter can make a big difference by itself.
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SAMFLUTCH
Used Cars

id say when the gear is set to neutral it would more efficient. coz i do it ever since the fuel prices have gone up and ive saved like £15 a week.

you'll b suprised on how much u'll save.

This message has been edited. Last edited by: Forum Moderator,

Well, i believe that it has been proven (read in driver's ed book) that the most effective speed to burn fuel is about 45mph.