Do Jake Brakes effect our Mileage (MPG) - Luxury Coach Lifestyles
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Old 09-06-2012, 07:46 PM   #1
Newell Attack
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Default Do Jake Brakes effect our Mileage (MPG)

Hi Guy's,

Question.... After having a new Jake Brake installed I have seen a decrease of mileage (hand calculated of course) with new jake my averages are 5.8 to 6.2. Prior to new jake I was averageing 6.5 to 7.5 Does my newly installed Jake brake effect my fuel mileage?

I do notice that when the Jake is engaged, there will be a bit of unburned fuel coming from the exhaust that

I can only see at night time when there are headlights shinning from behind.

Thanks in advance,

Newell Attack
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Old 09-06-2012, 09:58 PM   #2
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Hi Jeff,

In my opinion If you leave your jake on all the time your not going to get any coast out of your coach- I only use mine on grades

David
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Old 09-06-2012, 10:09 PM   #3
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Jeff, what engine are you running your coach the the 6v92, 555, 3208 or?


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Old 09-06-2012, 10:27 PM   #4
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Quote:
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Jeff, what engine are you running your coach the the 6v92, 555, 3208 or?


ken
Hi Ken,

Our Newell is equipped with the 6v92

Jeff
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Old 09-06-2012, 10:36 PM   #5
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If you leave the jake on all the time, thats like putting on your brakes every-time you take your foot off the accelerator.
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Old 09-06-2012, 11:12 PM   #6
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This coud get a little long, but this is a subject about which I was interested and did some digging and modifications.

Just a quick review of how the Jake ( compression ) brake works. It all happens on the compression stroke. On a normal compression stroke fuel has been draw in on the intake stroke and then that air fuel mixture is compressed on the compression stroke. Compressing a gas makes it very hot and the hot mixture combusts and with all the valves still closed that force pushes the piston down and makes your coach go. Ever notice how quickly the turbo spools up when you press on the go pedal - that's the result of those gases increasing tremendously in volvume due to their heating?
Now when the Jake comes into play you are off the "gas" pedal and no fuel should be flowing through the injectors. On the compression stroke there is no explosion since there is no fuel, but right at the top of the stroke the valves are suddenly opened. Now there is no compressed air to push the piston back down so all the work invovled in compressing that air is turned to heat and the coach slows. And yes, watch your turbo pressure when the Jake is on sometime, it jumps right up as the hot air rushes out the exhaust and spins it up. The sound your hear is the compressed air released at the top of each compression stroke. You have turned the engine into a huge air compressor and the energy to compress the air is recieved from the coach's motion. The higher the rpms, the more energy consumed.

How does all this affect mileage and when one should use their Jake. It is something each person must decide and I am only describing how I do it and why.
As has been pointed out if you desire to just coast and the Jake is on, you won't coast you will quickly slow and will have to apply throttle to attain your desired speed. That is not what I wanted. But if I don't have the Jake selected all the time what happens when I need to make a stop in a panic situation? Do you think I would be able to mash the service brake and remember to engage the Jake? I think there is little debate the Jake can help you stop the bus in a shorter distance. Well, don't know about you, but I would never be able to engage the Jake and panic brake at the same time without lots of practice and that just seem impractical. What I wanted was a Jake that functioned a bit differently. What if the Jake engaged when I pressed the service brake and stayed engaged until I touched the throttle? Well that is what I wanted and what I have. I think it works great. When cresting a hill on which I want to use the Jake I just touch the service brake, the Jake engages and all is good.
I did have someone point out that by having theirs engaged all the time that just as soon as they lifted from the throttle in a panic stop they would get compression braking. I agree that the part of a second it take me to move from the throttle to the brake they have compression braking and I don't. I hope it's never that close. Other than that, it works wonderful. If I lift from the throttle I coast. Other that leave the Jake on all the time apparantly learn to just hold enough pressure on the throttle to keep the Jake off but not use any fuel. I never could get that to work so well. Here is a company that seems to help with modifications if you want to use your Jake without having it slow you everytime you lift.

Brakeswitch, A better way to manage your diesel exhaust brake
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Old 09-07-2012, 01:09 AM   #7
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Quote:
Originally Posted by Newell Attack View Post
Hi Guy's,

Question.... After having a new Jake Brake installed I have seen a decrease of mileage (hand calculated of course) with new jake my averages are 5.8 to 6.2. Prior to new jake I was averageing 6.5 to 7.5 Does my newly installed Jake brake effect my fuel mileage?

I do notice that when the Jake is engaged, there will be a bit of unburned fuel coming from the exhaust that

I can only see at night time when there are headlights shinning from behind.

Thanks in advance,

Newell Attack

It is my opinion that there will always be a small amount of unburned fuel. There is always enough fuel from the injectors to maintain engine idle speed even with the Jakes engaged. Since the Jakes are opening the exhaust valves, this fuel is not burned and would appear as unburned fuel in your exhaust.

Again this is just my opinion
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Old 09-07-2012, 01:17 AM   #8
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Russ, good information. I have already asked for the BrakeSwitch information. For whatever it is worth, my owners manual states that use of the Jake will increase fuel consumption. While I do not like mine on all of the time in town, I leave it on when in hilly countryside.
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Old 09-07-2012, 01:28 AM   #9
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We have an '82 and without the Jacobs Brake we would have problems on the country roads! I leave the Jake on all of the time, I am an "old guy" and may forget. We get about 10 MPG towing or not, up a hill or down, 10 MPG!
You nay consider getting the Rack Adjusted and using the Cruise Control.
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Old 09-07-2012, 06:36 PM   #10
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I use the Jake intermittently, when going down grades, in any gear, and to slow at a stop light or sign and yes....I do think it changes fuel mileage.
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Old 09-07-2012, 06:49 PM   #11
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your millage is tied to your tune up. What were the injector settings before they installed the jakes. Go back to that setting and see if your millage returnes. You may also have an injector that is dribbling fuel into the cylinder when it is in the no fuel position ( foot off the go pedal ) coming to a stop or down hill operation with the jakes on.

Hope this helps
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Old 09-07-2012, 07:32 PM   #12
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I use the Jake brake for a different reason: to save my brake pads. A brake job on a Newell on front and rear wheels is a lot of money about $2,800. Using the Jake brake all the time enables me to use the service brakes less often.

South Louisiana is flat - no hills, but I still use the Jake. There are many instances that I slow down by just taking my foot off of the accelerator and coast to the traffic light. Sometimes I don't have to touch the brakes the Jake slows me down enough to wait for the green light.

Going broke - saving money!

Just my .02
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Old 09-08-2012, 04:23 AM   #13
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you mean that I could possibly get better mileage if I turn the Jake off and on? I will have to give this a try, as long as I can remember what I am doing..
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Old 09-08-2012, 04:45 AM   #14
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I think the mileage issue mentioned is directly relative to temp and driving conditions, wind, cool or warm weather, into the wind, w/ the wind, etc. The worst wind condition to affect mileage is a 45 degree cross wind so that something to keep in mind.

Joseph
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Old 09-08-2012, 05:25 PM   #15
Chester B. Stone, Jr.
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I have ordered the inexpensive BrakeSwitch. Makes a lot of sense and will enable me to leave the jake on all of the time in case of an emergency stop, but it will keep the jake from engaging unless the brake pedal is pressed. Without the BrakeSwitch, the jake engages every time I let up on the accelerator.
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Old 09-08-2012, 07:09 PM   #16
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The basic idea behind a Jake Brake is to use the engine to provide braking power.

A Jake Brake modifies the timing on the exhaust valves so that, when braking is desired, the exhaust valves open right as the piston reaches the top of the compression stroke. The energy gathered in the compressed air is released, so the compression stroke actually provides braking power.

The main advantage of a Jake Brake is that it saves wear on the normal brakes. This is especially important on long downhill stretches.
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Old 09-08-2012, 07:09 PM   #17
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Chester - I think you will love it, once installed. Please don't ask me how, as I stumbled around on it forever and I am supposed to be good at that stuff. Maybe you can keep some notes on how you do it for others. Good luck!
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