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Old 05-28-2011, 05:02 PM   #1
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Exhaust Brakes vs Fuel Mileage

Can anyone tell me if setting the exhaust brake switch to "high" or "on" appreciably affects fuel mileage?
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Old 05-28-2011, 05:17 PM   #2
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I use the exhaust brake only when needed. I see no difference in fuel usage.
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Old 05-28-2011, 05:23 PM   #3
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Like Gary, I use mine only when needed because I like the energy management aspect of driving. I'd like to think that coasting improves my MPG but my results don't support that.

Many folks like to have it on at all times and gut feel tells me that should yield lower mpg but maybe we'll hear from someone who's done a controlled experiment both ways.

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Old 05-29-2011, 03:43 PM   #4
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Like Gary, I use mine only when needed because I like the energy management aspect of driving. I'd like to think that coasting improves my MPG but my results don't support that.

Many folks like to have it on at all times and gut feel tells me that should yield lower mpg but maybe we'll hear from someone who's done a controlled experiment both ways.

Rick
I can't say for sure, but I would think that having the exhaust brake would decrease the mileage. But, it really does not make any difference since the exhaust brake is designed for temporary usage. I only turn it on when I am heading down a steep hill/mountain.
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Old 05-29-2011, 04:03 PM   #5
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According to Freightliners Mike Cody, it makes no difference in fuel mileage. Do make sure the brake is off when driving in rain, snow, ice...bad weather.
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Old 06-08-2011, 01:39 PM   #6
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Actually measured mileage on two identical trips (approximately 1400 miles RT), mostly interstate, Florida to East TN. There was no difference in fuel mileage. I feel more comfortable driving with the exhaust brake on. The only time it is off is in rain (never, ever, will I be anywhere where ice or snow are).
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Old 06-10-2011, 02:56 PM   #7
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I use the engine brake most of the time not because of fuel economy but it has to help with brake wear. I find that upon exiting the expressway and in many cases upon coming up on a trafic light I never have to touch the brakes until the last instant. Would love it if someone could tell me why I shouldn't be doing that!!!
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Old 06-10-2011, 05:55 PM   #8
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I use the engine brake most of the time not because of fuel economy but it has to help with brake wear. I find that upon exiting the expressway and in many cases upon coming up on a trafic light I never have to touch the brakes until the last instant. Would love it if someone could tell me why I shouldn't be doing that!!!
I have no interest in telling anyone else how to drive their coach, but I use mine only when needed on descents and sometimes on off ramps because I prefer to manage the inertia of the rig rather than having it try to stop itself each time I back off the accelerator.

Different strokes.

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Old 06-10-2011, 08:09 PM   #9
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There is no effect on fuel mileage when using your diesel engine brake, as it will not consume any fuel when used. It will, of course, slow your inertia, as your service brakes will. Slowing your inertia clearly does have an effect on fuel mileage.

With that said, my driving style is to always have my engine brake on, and I use it constantly when I need to slow the coach. It is programmed to only come on when I switch off the cruise control or touch the service brakes (with the brake switch on). If the cruse switch is on (not engaged) the engine brake will not come on, and I can coast w/o the engine brake coming on. The programming mode is called Latch Mode.

I also have my transmission programmed to shift only to 4th gear with the engine brake. It came from the factory as default to downshift to 2nd gear when the engine brake came on. I found this too agressive, and I really like how I have my coach programmed for driveability.
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Old 06-15-2011, 07:26 AM   #10
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I think that Pusherman pretty much explained it. The only thing I would add is if you leave it on all the time, you'll have to work your throttle a bit more careful, if it's left on, there is an area right after the pedal goes to idle to where you can coast without activating the exhaust brake. In stop and go traffic, if the brake is left on you can find yourself slowing more than needed which could cut your mileage down only a fraction of a mph if at all, otherwise, the exhaust brake has no effect on fuel mileage.
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Old 06-23-2011, 08:40 PM   #11
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The "engine brake" on our Allegro Bus is set so that it doesn't come on until you touch the brake (versus anytime you take your foot off the accelerator) so since I am slowing down, ie braking, the engine brake help is appreciated and saves on brake wear and does not reduce mileage.

If the E-B were set to come on every time you let off the accelerator (a setting that was available on our former Alpine Coach) there were times I wanted to "coast" without E-B holdback so I would reach over and turn the E-B off.
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Old 06-27-2011, 05:23 PM   #12
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I almost always drive with the engine brake set on LOW, and control it with the throttle position relatively easily to attain coasting when I want that. The Spartan two stage engine brake is a bit different from many of the exhaust type brake systems though?

I've seen many folks who have installed a " Brake-Switch " on their coaches which basically sets up the engine brake to only come on when they touch the service brake, not when they let all the way off the throttle. This might be something you would want, or not.

I think one needs to use the service brakes now and then, if nothing else but to keep em clean down there .....
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Old 06-27-2011, 05:53 PM   #13
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I don't quite understand why they say not to use the exhaust brake on wet or icy surfaces.

It seems to me that it is like using the engine compression to slow a vehicle, which I do in my car. I often shift my car into 2nd gear when on slippery roads, which allows me to avoid using the brakes. Now I wouldn't shift into 1st gear (or LOW on an automatic transmission) from 40 mph, that would break the friction between the tires and the slippery roadway; but applying the exhaust brake seems to be a very "gentle" reduction of inertia.

So, someone explain the rationale to me, so I don't have to try it to find out...
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Old 06-27-2011, 06:03 PM   #14
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Quote:
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I don't quite understand why they say not to use the exhaust brake on wet or icy surfaces.

It seems to me that it is like using the engine compression to slow a vehicle, which I do in my car. I often shift my car into 2nd gear when on slippery roads, which allows me to avoid using the brakes. Now I wouldn't shift into 1st gear (or LOW on an automatic transmission) from 40 mph, that would break the friction between the tires and the slippery roadway; but applying the exhaust brake seems to be a very "gentle" reduction of inertia.

So, someone explain the rationale to me, so I don't have to try it to find out...
The suggestion of not using exhaust brakes on wet or icy roads is for the same reason you cite to not shift into low. The concern is that you may lose traction because the transmission automatically starts downshifting when the exhaust brake is engaged. That downshift may cause a traction loss.
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