Engine Braking

[dan765]

I'm confused on this. It seems to me that since the engine spins faster while braking, then it is burning more fuel, so how is it more efficient?

[Daox]

Modern engines don't inject fuel while decelerating in gear.

[dan765]

ohhh i see. Thats interesting.
So pretty much the engine is turning but no fuel is being burnt?

[wyatt]

Yes, but the engine turning is slowing your vehicle down... so it is better than using your breakpads to slow down, but you don't coast as long as if you were coasting in gear.

[bestclimb]

I see it repeated all the time, I am curious why engine braking is better than using the pads? I definitely understand the concept on long hills where the pads will heat but for normal driving around town? Brake pads for a car are pretty cheap and easy to replace.

[MadisonMPG]

Most cars don't use gas when the engine is doing the braking. The clutch pad doesn't get too much heat from friction when engine braking either. The BEST way to slow down, is EOC to stop.

[bestclimb]

Agreed that best is EOC to stop. The clutch pad should not be getting any heat from friction while engine braking, as it should not be slipping (especially as it has less force on it than when under heavy acceleration)

[Christ]

Engine braking is better than using your brakes because your engine doesn't turn into dust.

There is a huge problem with brake dust on roads in California, because people think they should stomp on the gas, then stomp on the brake just as hard, instead of attempting to smoothly flow through traffic. It leaves brake dust on the roads, which in turn gets washed into water sources, asbestos and all. (Not that newer pads have asbestos in them, I don't think.)

[Arragonis]

Originally Posted by wyatt

Yes, but the engine turning is slowing your vehicle down... so it is better than using your breakpads to slow down, but you don't coast as long as if you were coasting in gear.

The trade-off can be difficult to calculate though. If I coast in gear then I use no fuel and with long gearing (30mph / 1000rpm - 6sp Diesel) I can coast for a long time and my MPG reads at infinity. If I coast out of gear I can go slightly further but then engine is burning fuel to keep going and MPG depends on speed, can be between 40-65.

I'm interested in working out whether its better to accelerate more strongly uphill that try to cruise for longer at a lower throttle, and also whether its better to be in a lower gear (less effort but more RPM) vs a higher one. My experimentation so far has not been conclusive.

(All figures Imperial)

[tjts1]

If you're braking in neutral, the engine is idling and burning gas.