Exhaust Brake Question

[JohnBower]

I have seen a couple of comments on this forum about the exhaust brake on the 6. 7's having improved mileage when it's off. Does anyone know how this would happen?

 

[RVTRKN]

I've heard of it, but mine is the same either way hand calculated, although mine is the C&C/305 HP version.

 

[HBarlow]

I have seen a couple of comments on this forum about the exhaust brake on the 6. 7's having improved mileage when it's off. Does anyone know how this would happen?

Erroneous perception.

There is no way that allowing the exhaust brake to function to slow the truck when fueling and boost are shut off could reduce fuel economy.

 

[jgillott]

Erroneous perception.



There is no way that allowing the exhaust brake to function to slow the truck when fueling and boost are shut off could reduce fuel economy.

Actually, that is not exactly 100% correct. That would be correct only if the driving sample, that was being used for measuring fuel mileage, required only two driving modes... under throttle and braking. Though they may be only brief periods of time, there are certain situations in that sample drive where your vehicle would be coasting and not needing throttle or brake input. In theory, if the exhaust brake is left on all the time, those coasting situations would be changed to "braking" modes, thus reducing forward momentum, and reducing potential fuel mileage over that given driving sample. Now, that difference may be extremely small. But in theory, use of the exhaust brake at all times could in fact reduce fuel economy under the right conditions.

 

[HBarlow]

Yes, you make a good point. In theory what you wrote could be accurate but the difference would be miniscule. Most defensive drivers accustomed to driving with an exhaust brake watch ahead for traffic changes and allow their vehicle to slow slightly with traffic w/o defueling and activating the EB.

If you are talking about someone who is seriously driving for economy by relying on coasting as much as possible like the old Mobil Oil fuel economy competitions of many years ago I'd agree with you.

I think any possible savings achieved by not using the eb would be spent instead on slightly accelerated brake pad wear.

I've driven three Dodge-Cummins Rams about 600k miles with exhaust brakes. I'm a believer!

 

[hwebster]

Okay. . On my '08 high driving at highway speed, Brake off = ~1-2MPG higher - computer reading only!

 

[Lil' Dog]

I have seen zero difference. Being that the EB is only active when your APPS is at 0 position, I can't see how it would affect your highway mileage.

 

[SNGLESHOT]

I agree with you lil dog. While I only have 13K on my 2008, I drive all the time with the EB on now after trying it both ways and have seen no difference in MPG. I am getting 18 city and 21 hwy. not too shabby for a 6. 7 big truck. Really happy.

 

[hwebster]

I can't explain it other than I don't trust the overhead for MPG but go cruise with it on and then off and watch the numbers creep up. Happens pretty quickly!

 

[Lil' Dog]

I wouldn't trust the OH display either. . Only thing I can surmise if you are on some rolly highway and it engages once and a while instead of coasting? I dunno. .

 

[RVTRKN]

I wouldn't trust the OH display either. . Only thing I can surmise if you are on some rolly highway and it engages once and a while instead of coasting? I dunno. .

After a few long trips, recording hand calculated numbers as well as recording the OH, it was so close, I now rely on the overhead for a average MPG when needed. I would be able to see a difference in the OH, if it was critical, but only in a proper test would you be able to determine one way or the other.



Maybe the next long trip I go on, I will experiment with it on and off, but I need the EB with a GCVW at 22K, and probably will not. I believe the numbers are so close either way, that it really doesn't matter to me anyway. I'm not going to dispute any other posts on this topic, but I think the only theory that I would believe, is the fact that momentum is lost on the braking action in city driving conditions and would cause a difference in MPG. But then again at 10,500 GVW I need the exhaust brake to prevent premature wear on my brakes, and like the fact that after 25K there is little wear on them.