Does engine braking actually save gas?

[noginsk]

Ever since I put my deposit on a tC, I hae been visiting http://www.scionlife.com. The site has lots and lots of people on it, and wading through the crap that people write seems daunting at times. So, I thought that maybe since genvibe members seem more educated, I'd give you all a shot at answering this. This link is discussing wether you get better gas mileage by engine braking or by shifting into neutral. I see believable stories for both side, although I tend to believe that shifting to neutral is better. What does everyone think? http://www.scionlife.com/forum...23539

[ragingfish]

My uneducated theory is this:Shifting into neutral and using only the brakes saves gas because when you downshift, the engine revs up and then has to work to slow down...thus expending gas...if you remove the resistance from the engine, while the revs go up, it doesn't have to work as hard to move the car (it's actually nort working to move it at all) so it slows down quickly...HOWEVER -- it's never adviseable to neutral-shift and use only your brakes for braking. It cause premature wear and, in some cases, can cause your brakes to overheat (i.e. riding the brake while coasting downhill).I personally choose to downshift, even on an auto, whenever possible, to minimize break wear...

[Mavrik]

I was always told by people older and smarter then me that down shifting saved your brakes and manuals were always better on fuel then an automatic...Also at least here anyway if I were taking a driving test in a manual and shifted it into neutral and used the brakes to slow down I would instantly fail... Simply because if I suddenly needed to get the car moving? I'm in neutral...I really hate it when I come up behind someone in a 50km zone and they ride their brakes the whole way down very gradual hills and slight curves... they are the people that complain to me, "my brakes can't be gone already!"

[MadBill]

Even on a carbureted car, any minute fuel savings due to braking in neutral would be offset by the increased wear on the brakes, as they would have more work to do. Modern fuel injected engines use no fuel during deceleration, since the injectors switch off after a second or so, and come back on only at low RPM or if you step back on the throttle. (with a manual transmission vehicle, you can often feel a slight 'bump' as this occurs)Except for long, steep downgrades which can overheat the brakes, it's normally better to leave the transmission to transmitting power and let the brakes do the braking.

[joatmon]

I use the brakes more than the engine to slow down. brake pads are pretty easy to replace,

[B18B]

While I choose to regularly downshift while braking, I would have to agree with MadBill that the most proper way of decellerating (ie: Ministry of Transport approved way) is to leave the car in the gear while braking. I believe this would likely afford the best compromise between brake life (still a small degree of engine braking), clutch longevity, fuel economy and driver attention.In a kinda related topic, for those of you who do keep the car in gear while braking, have you found that there is a point where you can just pop the car out of gear without using the clutch? Does anyone know what this point is called!?!??

[JohnC]

This link is discussing wether you get better gas mileage by engine braking or by shifting into neutral. http://www.scionlife.com/forum...23539 [/QUOTE]Leaving out all the other reasons weather you should leave it in gear or not and just focasing on the fuel mileage question...the throttle is closed if you are in neutral or coasting in gear, either way takes the same amount of fuel. Now if you shut the engine off...

[Roadpig]

....brake pads are pretty easy to replace,I agree, brake pads are much easier & cheaper to replace vs a new clutch. Plus, GT's are known to have premature wear on the clutch, so anything I can do to minimize wear.

[joatmon]

Quote, originally posted by MadBill » Modern fuel injected engines use no fuel during deceleration, since the injectors switch off after a second or so, and come back on only at low RPM or if you step back on the throttle. (with a manual transmission vehicle, you can often feel a slight 'bump' as this occurs)so, when engine braking, the RPMs are higher than if the car was idling, but the fuel injectors shut off and provide no fuel?

[noginsk]

Quote, originally posted by joatmon »so, when engine braking, the RPMs are higher than if the car was idling, but the fuel injectors shut off and provide no fuel?That is kind of what I am gathering here. The engine will need to keep itself running, and with out being connected to the gears direclty, when in neutral, it will fire the injectors (using fuel) to keep the engine running. When in gear, and slowing down, the momentum of the the car keeps the engine turning and therefore no fuel is needed from the injectors to keep the engine "on". At least this is what I am lead to believe. It's weird too. I had always thought that it was better to shift into neutral to save gas while slowing down. I had always done it this way too.

[MadBill]

That's correct, nog, no need for fuel on deceleration! There were a few carbureted engines that used solenoids to shut off the fuel when decelerating, but they were hard to make operate correctly. (If you were to suddenly depress the clutch on such a system, the engine might stall before the fuel delivery could restart.)