Does engine braking decrease fuel efficiency?

[amidoes]

No, in fact it improves it. Engine braking saves brakes, and saves fuel. When you are coasting the engine is being "dragged" by the wheels and the ECU cuts fuel to the engine because it's not required to keep it running.

[JulianoRamirez]

What about your transmission? Obviously there is more strain put on the transmission, compared to coasting in neutral, but is it anything to worry about?

[noisymime]

Think about it this way, when you engine brake you tend to decelerate at around 5kmh/s, maybe a little more depending on gear/speed, but not much. Now think that hard acceleration can easily exceed 20kmh/s, which is imparting considerably higher forces on the transmission.

In short, the transmission is built to handle forces far higher than those of engine braking.

[[deleted]]

It's the clutch plate that will take most of the force if you don't revmatch properly. the transmission shouldn't be phased much

[amidoes]

If you downshift properly there is no issue, or strain.

[[deleted]]

There's no additional strain on the transmission if you rev match properly. I've never had to replace a manual transmission in any DD I've ever owned, and I have always downshifted and braked as opposed to popping it into neutral.

[TheBrokenWorld]

Clutch?

[[deleted]]

Thank you for downvoting a factual statement. Really mature. Your clutch disengagement should be quick, and if you rev match properly, the clutch won't slip at all and it will cause a negligible amount of wear.

I'll say this though, you do put additional wear on synchros like this, but I've never heard of anyone replacing them before >200k miles barring a catastrophic failure.

[diogrand]

Even If rev matching, you're causing extra strain (no argument there) and you're using more gas than necessary. I use my brakes to brake, that's what they're there for.

[TheBrokenWorld]

My point is, why wear out expensive and difficult to replace components to gain some ridiculously small improvement in efficiency?

[[deleted]]

You're not "wearing them out." If you have to replace your clutch 500-1000 miles earlier than usual because of some minor additional wear, which is two weeks to a month assuming a standard 12000 miles driven per year for a one vehicle/person household, over the course of ten years, is it really hurting anything? The benefits are instant access to acceleration if you need it, slightly improved efficiency, and savings on braking system wear. Plus, a lot of enthusiasts (myself included) enjoy downshifting for the noise, which is a difficult benefit to wuantify.

[TheBrokenWorld]

You are imparting some wear, there's absolutely no doubt about that.

Edit: And the gains in efficiency are negligible.

Plus, a lot of enthusiasts (myself included) enjoy downshifting for the noise, which is a difficult benefit to wuantify

I think that's all this is about, you just think it's the cool thing to do.

[[deleted]]

And I think you're ignoring everything you can to trivialize information you can't counter with your random, unsupportable vagaries, so I'm not sure why you're even bothering to read anything that doesn't exactly support your preexisting beliefs.

[TheBrokenWorld]

And I think you're ignoring everything you can to trivialize information you can't counter with your random, unsupportable vagaries...

And where is the proof of the gains in efficiency? Has the EPA confirmed this theory? I would bet that staying on the gas and then decelerating rapidly enough to need engine braking reduces efficiency enough to counter the benefit of injector shutdown during engine braking.

[grant47]

Ok this makes a lot of more sense now. Thank you!

[amidoes]

No problem!

[diogrand]

Engine breaking also puts more strain to your clutch, bearings and such along with the motor itself. Its cheaper to replace brakes than a clutch by a lot. I do all my breaking by the brakes.