Originally Posted By: dja4260
Coasting to a red right isn't acceptable? Regardless, the clutch will be used once. I typically coast when approaching a red light attempting to not brake. (not break)
There are generally at least two benefits to coasting in gear vs. in neutral:
1) Deceleration fuel cut-off, often initialized as "DFCO". If you're in gear, with the momentum of the vehicle keeping the engine going, your engine computer will often completely cut fuel, meaning you're truly using ZERO fuel. In contrast, if you coast in neutral, your engine computer cannot cut fuel because it has to keep the engine spinning by burning gas rather than by using the car's momentum.
2) If you have a belt-driven power steering pump, you sure don't want the engine to actually stop turning, because you suddenly lose power steering. If, for some reason, the engine were to stall or lose fuel (fuel pump failure, etc) and you're coasting in neutral, you'll lose power steering and you'll have enough vacuum reserve for just one use of the brakes. In contrast, if you're coasting in gear, your engine will continue to turn due the car's momentum and you'll have more time to react to any lights on the dash that pop up because of the problem.
Moral of the story: there are few cases where it's legitimately "better" to coast in neutral. Coast in whatever gear you're in for as long as possible, and then pull it out of gear at 1,000 rpm or so to let the engine idle.