# Engine Braking with Diesels



## AzNMpower32 (Oct 23, 2005)

Given that diesel motors are inherently so efficient and don't generate much engine braking even at higher revs, is there any point in downshifting for a steeper gradient? Or does one simply rely on the brakes for prolonged mountain descents?

I've gotten quite used to letting the engine assist with the braking down steeper hills- In my petrol X3, I drop to 3rd @ 100km/h on a 8% gradient on US 421 at the Eastern Continental divide and let it run 4500rpm for a few kms without the brakes. Wonder if I should/could do this with a future diesel vehicle.


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## floydarogers (Oct 11, 2010)

AzNMpower32 said:


> Given that diesel motors are inherently so efficient and don't generate much engine braking even at higher revs, is there any point in downshifting for a steeper gradient? Or does one simply rely on the brakes for prolonged mountain descents?
> 
> I've gotten quite used to letting the engine assist with the braking down steeper hills- In my petrol X3, I drop to 3rd @ 100km/h on a 8% gradient on US 421 at the Eastern Continental divide and let it run 4500rpm for a few kms without the brakes. Wonder if I should/could do this with a future diesel vehicle.


I do it all the time. Gotta watch the revs, however - more like 2500-3000 rpm is the sweet spot for compression braking on the diesel.


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## Flyingman (Sep 13, 2009)

Clearly the OP has never driven a diesel, or a 335D for that matter!:yikes:

C'mon lad, the 335D, with all that torque in accelerating, just put that in reverse while downshifting. I use my paddle shifters to downshift almost exclusively and only use the brakes when absolutely required.

As for RPMs, well the computer won't let you down shift into 2nd if your traveling at 60mph. You can work what down the ladder very nicely but you need to be in the 40mph or less range before it will hit 2nd. I don't down shift into 1st as I don't want to drop my tranny with all that torque working it's way back into the engine. Plus you have to be nearly 10mph to drop it in.

Give it a try sometime.:thumbup:


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## SennaVProst (Apr 9, 2011)

I find that my D has quite a bit of engine braking actually, if I let go of the accelerator (especially when it's cold out), I can noticeably feel the deceleration as opposed to popping it into neutral.


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## Pasa-d (May 7, 2011)

In an automatic transmission car, it's the tranny that decides how much "engine braking" you are going to experience, regardless of the engine type. If the tranny decides to freewheel on deceleration, you aren't going to get any "engine braking" at all. I believe that many modern cars have automatic transmissions programmed to provide just enough back torque to the engine upon deceleration so that the fuel supply to the engine can be cut off but the engine remains turning, this provides maximum fuel economy. I believe the transmission design manual mentions such programming.

Personally, I find that on flat and level roads my car provides very little engine braking. I often find that as traffic slows and I lift off my foot I still have to brake to prevent running up into the traffic in front. Going downhill, it does seem to act differently and it does provide some engine braking effect. I will often downshift into as low as 4th to enhance this effect on long downhill sections.


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## AzNMpower32 (Oct 23, 2005)

I've driven my father's X5 diesel quite a few times; it never seems to have the engine braking that the 325i or my X3 has, although the X5's additional mass (and thus, momentum) may have something to do with it.

I know that in our two petrol BMWs, I can coast the vehicle quite often in gear (D) because the transmission slows the vehicle quite a bit even down gentle descents. So perhaps it may just be a vehicle-specific thing I guess?


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## listerone (Jul 21, 2009)

I've been wondering about this myself.I've never done any driving that involved steep downgrades but I will soon be visiting Mount Washington,NH and am also seriously contemplating a road trip over the Rockies (I-70).My "d" didn't have paddle shifters but my Blutec does and I'm wondering how one learns to use them in hilly terrain? Trial and error or is there an easier way? I know that one must watch the RPMs,particularly with a diesel but aren't our cars programmed to not allow dangerously high RPMs? As you can probably tell I've never owned a stick but,believe it or not,I have driven one a few (and *only* a few) times.


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## jashearer (Nov 9, 2011)

Throw a jake brake on that ****** 

Jay


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## Snipe656 (Oct 22, 2009)

Pasa-d said:


> Personally, I find that on flat and level roads my car provides very little engine braking. I often find that as traffic slows and I lift off my foot I still have to brake to prevent running up into the traffic in front.


I do not get this at all in my 335d. I routinely pull up to stops without barely even getting on the brakes. In traffic I routinely am able to "idle down" for slow spots in the stop-n-go and to the point where sometimes feel like I am going to get rear ended because people don't realize the car is slowing down. I am not though forcing downshifts or going into DS mode, just normal old D mode.


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## floydarogers (Oct 11, 2010)

Snipe656 said:


> I do not get this at all in my 335d. I routinely pull up to stops without barely even getting on the brakes. In traffic I routinely am able to "idle down" for slow spots in the stop-n-go and to the point where sometimes feel like I am going to get rear ended because people don't realize the car is slowing down. I am not though forcing downshifts or going into DS mode, just normal old D mode.


This is my experience.

Because the torque converter is almost always locked on the ZF transmission (unlike older "free-wheeling" transmissions), you always have compression-braking when off-throttle. The big tires of the sports package have a lot of rolling resistance, too.


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## Snipe656 (Oct 22, 2009)

Mine just has the non sports tires but still does it. This is actually one of the traits I like about every diesel vehicle I have put a fair amount of miles onto. I do not know if all diesel vehicles do it but thus far everyone I have decent experience levels with does. I also assumed the big reason was because of the higher compression engines but never really put a lot of thought into the reasons.


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## boooomer (Apr 23, 2010)

jashearer said:


> Throw a jake brake on that ******
> 
> Jay


Jake brakes are used on large diesel trucks and motorhomes with substantial towing capacities. They're used to save wear and tear on the brakes and transmission. I'm not certain exactly how they work but I think they create back pressure on the engine without downshifting the transmission. Again to save wear and tear on the tranny.

Our cars obviously don't have jake brakes so using engine compression braking by downshifting will cause the strain on the auto transmission that jake brakes were designed to avoid. Unless you're going down Mt. Washington, or any other very long very steep grade (where brake fade could be a problem), I think it's best to use the brakes on our cars rather than strain the tranny.


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## wanderlust (Feb 19, 2012)

all I know is new brakes are cheaper then a new transmission

powered by lemings


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## Snipe656 (Oct 22, 2009)

Jay brakes are on 3/4 ton diesel pickups these days.


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## need4speed (May 26, 2006)

wanderlust said:


> all I know is *new brakes are cheaper then a new transmission*
> powered by lemings


This is my philosophy too. N4S


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## JAPearson (Sep 9, 2011)

jake brakes work by keeping the exhaust valve closed until the last possible second. Some small truck have exhaust brakes, just a valve that closes off exhaust pipe, much less effective but helps.


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## bimmerdiesel (Jul 9, 2010)

wanderlust said:


> all i know is new brakes are cheaper then a new transmission
> 
> powered by lemings





need4speed said:


> this is my philosophy too. N4s


+1


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## Flyingman (Sep 13, 2009)

Pasa-d said:


> In an automatic transmission car, it's the tranny that decides how much "engine braking" you are going to experience, regardless of the engine type. If the tranny decides to freewheel on deceleration, you aren't going to get any "engine braking" at all. I believe that many modern cars have automatic transmissions programmed to provide just enough back torque to the engine upon deceleration so that the fuel supply to the engine can be cut off but the engine remains turning, this provides maximum fuel economy. I believe the transmission design manual mentions such programming.
> 
> Personally, I find that on flat and level roads my car provides very little engine braking. I often find that as traffic slows and I lift off my foot I still have to brake to prevent running up into the traffic in front. Going downhill, it does seem to act differently and it does provide some engine braking effect. I will often downshift into as low as 4th to enhance this effect on long downhill sections.


Taking your foot off the fuel pedal is not downshifting, which what we are trying to establish here.

I use my cruise control often and if you "downshift" on the speed control the vehicle will really slow down fast without downshifting. I assume it is controlling all of the hydraulics in the auto tranny turbine, because it slows the car down faster than downshifting.

Again, I use the downshifting all the time and only brake in an emergency or to make that final stop. I also anticipate well in advance I'm going to need to stop so start downshifting. I have no idea the condition of my brakes, they haven't been worked on yet (other than brake fluid at last service).

If this car had a manual transmission would you downshift? Absolutely.:eeps:

The paddle shifters are not there for decoration folks, use them! Heck, you paid an extra $100 to have them there!:thumbup:

If anyone can identify any literature that would indicate that downshifting our auto trannys is somehow harmful to our vehicles, kindly post it.


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## Flyingman (Sep 13, 2009)

AzNMpower32 said:


> I've driven my father's X5 diesel quite a few times; it never seems to have the engine braking that the 325i or my X3 has, although the X5's additional mass (and thus, momentum) may have something to do with it.
> 
> I know that in our two petrol BMWs, I can coast the vehicle quite often in gear (D) because the transmission slows the vehicle quite a bit even down gentle descents. So perhaps it may just be a vehicle-specific thing I guess?


Are you downshifting or just coasting to a stop?:dunno: If you aren't actually downshifting the Transmission, I can't really understand your argument.

If you put a 335D and a 335i next to each other on the highway going 80mph and both take their foot off the gas, which one will coast to a stop sooner? Who cares about that?

We are talking about the ultimate driving machine. Use the gears, please!


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## Snipe656 (Oct 22, 2009)

If you want to know the estimated remaining life on your brakes then scroll through the service menus when the car is at a stop. I for example should need rear brakes around 30-31k miles if the estimate holds true. Then I'd need front brakes WAY after that.


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## AzNMpower32 (Oct 23, 2005)

Flyingman said:


> Are you downshifting or just coasting to a stop?:dunno: If you aren't actually downshifting the Transmission, I can't really understand your argument


The extra forward momentum is noticeable day-to-day. However, there have been instances down steeper gradients where I've downshifted the X5 to 2nd or 3rd gear (2500-4000rpm) and really didnt notice much more engine braking effect.


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## Snipe656 (Oct 22, 2009)

AzNMpower32 said:


> The extra forward momentum is noticeable day-to-day. However, there have been instances down steeper gradients where I've downshifted the X5 to 2nd or 3rd gear (2500-4000rpm) and really didnt notice much more engine braking effect.


Wouldn't it be better to downshift to an rpm range within the high torque making range?


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## Flyingman (Sep 13, 2009)

There is a lot of debate about downshifting or braking. I actually use a combination of both when you get down to it. I definitely make a conscious decison to downshift before a stop or when coasting to a stop.

I suppose I'm substituting the paddles for the manual stick and clutch I originally learned to drive on. It was an old VW Bettle Bug 1300 I think.

If it was really bad for the car I suppose the engineer's would not have put the paddle shifters there, don't you think?:dunno:

Driving styles are like opinions, and not like @ssholes, as everyone has more than one!:rofl:


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## Snipe656 (Oct 22, 2009)

I don't have paddles on my car so guess it was not engineered to downshift when coming to a stop


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## Flyingman (Sep 13, 2009)

Snipe656 said:


> I don't have paddles on my car so guess it was not engineered to downshift when coming to a stop


It is if you have steptronic. All they did was mirror the controls from the shift lever up to the steering column, so you can keep two hands on the wheel.:thumbup:


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## Pasa-d (May 7, 2011)

The presence or absence of "paddle shifters" has nothing to do with this discussion. You can achieve the same thing by moving the shift lever up and back in the left position. I have paddles in my car but only for resale value. I don't use them, even at the track. I always use the lever.


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## Snipe656 (Oct 22, 2009)

Flyingman said:


> It is if you have steptronic. All they did was mirror the controls from the shift lever up to the steering column, so you can keep two hands on the wheel.:thumbup:


I know. I have no good reason for this but paddle shifters have zero appeal to me. I have even had car salesmen point out when driving "sports cars" how they find it odd I do not even touch the paddle shifters.

BTW I do not downshift even my MT car when coming to a stop. Only time I downshift that car is if I slowed down to a speed that is too slow for the current gear and I need to speed up or cruise. I do not even use the clutch to take it out of gear when coming to a stop but instead wait until down to the "idle" speed and just push the shifter out of gear. Maybe I will kill it with this horrible driving technique but heck that transmission is over 40 years old and never been torn into, so I will not get butt hurt if I ever break it.


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## Flyingman (Sep 13, 2009)

Pasa-d said:


> The presence or absence of "paddle shifters" has nothing to do with this discussion. You can achieve the same thing by moving the shift lever up and back in the left position. I have paddles in my car but only for resale value. I don't use them, even at the track. I always use the lever.


So if you have the choice of keeping two hands on the wheel and shifting or taking your right hand off and driving one handed, why would you choose the later?:dunno:

Both mechanically accomplish the same thing, and I would offer up that the paddle shifters are actually quicker, flick of a thumb or finger vs an arm and wrist movement, and you get to keep both hands on the wheel.

I can see it now, someone is going to drag race two 335d's, one with paddle shifters, the other just with steptronic!


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## dunderhi (Dec 10, 2006)

Pasa-d said:


> Personally, I find that on flat and level roads my car provides very little engine braking. I often find that as traffic slows and I lift off my foot I still have to brake to prevent running up into the traffic in front.


+1

I find my 335d coasts better than any of my previous cars, which I see as a contributor to its great fuel efficiency. :thumbup:


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## bayoucity (Jun 11, 2010)

Snipe656 said:


> ... I do not even use the clutch to take it out of gear when coming to a stop but instead wait until down to the "idle" speed and just push the shifter out of gear. Maybe I will kill it with this horrible driving technique but heck that transmission is over 40 years old and never been torn into, so I will not get butt hurt if I ever break it.


I have heard folks mentioning clutchless shifting, but I'm too chickken to attempt it. One of my staff was bragging about clutchless shifting on his boxster from 3rd to 4th or vice versa the other day. I'll try it eventually if I can obtain a MT rental car.


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## Snipe656 (Oct 22, 2009)

I was not referring to really clutchless shifting. If you are coming to a stop with an MT you can pull it out of gear without using the clutch so long as your engine speed is correct for the task. I used to sometimes clutchless shift one of my old trucks. It is not really hard to do, I learned how when linkage broke for the clutch and still needed to get home. 

I have read plenty of things that show proof that downshifting in gas cars does not truly help braking. I used to do it all the time because liked hearing the exhaust drone.


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## Philm35 (Aug 19, 2010)

In my experience, downshifting makes more noise than deceleration. All of my previous gas-engined cars had far more effective engine braking than my 335d.

For those who use engine braking and downshifting to save wear on the brakes, ask yourself this... Why would you want to put additional wear and tear on your engine, transmission and driveline (worth many, many thousands of dollars) instead of your brake pads and rotors, costing a few hundred bucks?

You're kidding yourself if you don't think that sudden application of torque and revs resulting from hard downshifts isn't putting strain on your driveline. Use the brakes. That's what they're for.


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## floydarogers (Oct 11, 2010)

*The Auto transmission downshifts anyway*

Folks, as far as wear is concerned, you're all ignoring the normal action of the ZF auto transmission's programming.

If you are slowing down (either coasting on the flat or by applying the brakes), the transmission will downshift until you're going quite slow (~20mph when it gets to 2nd gear).
This requires no action on your part: the ECU/transmission controller does this to maintain enough rpms to keep the turbos spun up.


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## Philm35 (Aug 19, 2010)

> Folks, as far as wear is concerned, you're all ignoring the normal action of the ZF auto transmission's programming.


Agreed... But when you force a downshift, suddenly bumping up the revs, putting a sudden heavy load on the drivetrain, IMHO that is adding much more severe wear and tear on the drivetrain than the normal downshifting that occurs when the car slows down via coasting or braking.


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## Flyingman (Sep 13, 2009)

Well, I use it because I enjoy doing so. Gives me the best of both AT and MT, which is why BMW put the Steptronic and paddle shifters there in the first place.

Found these instructions:

Print this articleInstructions

1 
Move the transmission knob into "D." This is Mode 1 of 3 on this transmission. Use this mode for everyday driving and if you simply want to relax and cruise in your BMW. While in D mode, the transmission will shift smoothly and quickly to give the driver the smoothest ride and the best fuel economy by shifting into the highest gear as quickly as possible.

2 
Move your transmission knob to the left. This is Mode 2 of 3 on this transmission. This is called the DS (Drive Sport) mode. Use this mode if you are planning to accelerate fast from a stop light or about to use a freeway on ramp. While in DS mode, the transmission will stay in each gear longer to give the driver optimum performance.

3 
Move the transmission knob down. This is Mode 3 of 3 on this transmission. This is called "M" (manual) mode. When you move the knob down, the transmission will shift into a higher gear. Move the knob up, and the transmission will shift into a lower gear. The BMW also has paddle shifters located on the steering wheel. The right paddle is for the upshift and the left paddle is for the downshift. When shifting using M mode, you do not lift your foot off the gas. Likewise, if you accidentally do something that could damage the transmission, the computer will take over to preserve the transmission. When using M mode, make sure to use the transmission as you would a real manual. If you slow down, you need to downshift. If you do not downshift, the transmission will downshift to the appropriate gear for you. However, the transmission will not automatically upshift for you.
Use M mode if you want to shift the car on your own, or if you are at the race track. Racers like to use the M mode to keep the car in a particular gear. Since racing is all about time, if the racer can keep the car in 2nd gear while going into a turn, he gain a slight advantage over the racer that allows the car to shift into 3rd gear and then to 2nd gear while in the turn.

Read more: How to Use a BMW Steptronic | eHow.com http://www.ehow.com/how_5097735_use-bmw-steptronic.html#ixzz1vmbTcqo4


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## Snipe656 (Oct 22, 2009)

Crap, I have not been using DS for on ramps this entire time ... good thing I read this now since not left the house yet


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## Axel61 (Mar 10, 2011)

I did NOT care for the paddle shifters they confused me the steptronic does also, coming from 9 yrs with an 02 MCS. I used to engine brake with it but got away from it, caused to much strain I believe in the car, as far as doing it with the 335d Ive done it a couple of times and came to a conclusion duh!! I have an AT transmission, plus iM GETTING OLD FOR IT lol


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## swood02 (Nov 30, 2010)

I've used the adaptive cruise control on my 335D to slow the car on hills. Just pull the cruise control lever back towards you (like reining in a horse). It slows the car in 1- or 5-mph increments depending on how long you pull back on the reins. I've watched the revs and not noticed anything alarming.


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## floydarogers (Oct 11, 2010)

swood02 said:


> I've used the adaptive cruise control on my 335D to slow the car on hills. Just pull the cruise control lever back towards you (like reining in a horse). It slows the car in 1- or 5-mph increments depending on how long you pull back on the reins. I've watched the revs and not noticed anything alarming.


That's because it uses the brakes to slow the car.


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## Flyingman (Sep 13, 2009)

I thought that might be the case, as rpm is not really affected and the braking is right now.

Learn something new everyday!


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