Exhaust Brake ON whith Cruise Control ON??

[supercub]

I usually have the exhaust brake off, and turn it on when I need it. The other day, I had forgot and left it on. I had the cruise control set and started going down a long grade. As the speed picked up, the exhaust brake came on..........does this hurt anything to have the exhaust brake working with the cruise control on? Thanks
Brian

[wolfe10]

Spizzer wrote:

Ray,IN wrote:

wolfe10 wrote:
I am not sure that use of the exhaust brake is hard on the exhaust manifold.

Remember, with the throttle closed, ZERO fuel is injected. Zero fuel means zero additional heat. So, if the manifold is hot from a long climb, once you crest the hill, I don't see a problem with the exhaust brake on-- that will slow the cooling rate, but certainly not add to the heating rate.

How does a diesel idle if ZERO fuel is injected? Isn't the throttle closed then?

Ray, I assume it is like most modern cars with fuel injection, when coasting and engine rpm is above the idle set, it shuts off the injectors electronically. When rpm drops, it turns them back on.

Jeff

Correct. As idle speed is approached, fuel injection begins again.

And, if the exhaust brake did not automatically open at low RPM/as you approach idle speed, the engine would die as well.

[Spizzer]

Ray,IN wrote:

wolfe10 wrote:
I am not sure that use of the exhaust brake is hard on the exhaust manifold.

Remember, with the throttle closed, ZERO fuel is injected. Zero fuel means zero additional heat. So, if the manifold is hot from a long climb, once you crest the hill, I don't see a problem with the exhaust brake on-- that will slow the cooling rate, but certainly not add to the heating rate.

How does a diesel idle if ZERO fuel is injected? Isn't the throttle closed then?

Ray, I assume it is like most modern cars with fuel injection, when coasting and engine rpm is above the idle set, it shuts off the injectors electronically. When rpm drops, it turns them back on.

Jeff

[Ray_IN]

wolfe10 wrote:
I am not sure that use of the exhaust brake is hard on the exhaust manifold.

Remember, with the throttle closed, ZERO fuel is injected. Zero fuel means zero additional heat. So, if the manifold is hot from a long climb, once you crest the hill, I don't see a problem with the exhaust brake on-- that will slow the cooling rate, but certainly not add to the heating rate.

How does a diesel idle if ZERO fuel is injected? Isn't the throttle closed then?

[two-niner]

You are riding with one foot on the gas pedal (diesel) and one foot on the brake.

Unless you are on very long and steep grades.

[wolfe10]

I am not sure that use of the exhaust brake is hard on the exhaust manifold.

Remember, with the throttle closed, ZERO fuel is injected. Zero fuel means zero additional heat. So, if the manifold is hot from a long climb, once you crest the hill, I don't see a problem with the exhaust brake on-- that will slow the cooling rate, but certainly not add to the heating rate.

[Ray_IN]

The Cummins 8.3 is known for cracking exhaust manifolds. It is my opinion, overuse of the exhaust brake may contribute to overheating the exhaust manifold, which in turn may be the cause of cracking. I only turn mine on when needed, otherwise I cannot use downgrade momentum to my advantage, while hopefully avoiding a cracked exhaust manifold.

[Spizzer]

Ivylog wrote:
Brian, no it .....
Using "air brake" twice and "unless the brake is depressed", Jeff you really did mean the MH's air brakes.:S

Oops. You are correct....I mean exhaust brake.... Thanks.

jeff

[supercub]

Cummins ISC 8.3 350hp

[wolfe10]

Tell us what engine you have and we can give better advice. There are options on some as to how the exhaust brake is controlled.

[donn0128]

If your driving a Ram, leave the EB on all the time except in slipery conditions. Saves a lot on the service brakes.

[Ivylog]

Brian, no it does not hurt anything other than your MPG. In hilly terrain at the bottom of the hill where I can see what's coming up next, I'll be 5-10 MPH over the speed limit and manually accelerating even with the cruise on.
Using "air brake" twice and "unless the brake is depressed", Jeff you really did mean the MH's air brakes.:S

[Spizzer]

Doesn't hurt anything because as soon as the cruise control adds throttle, the air brake goes off. It is just not efficient driving to add braking every time you take your foot (or the cruise control does) off the throttle. Not to mention the wear and tear on the transmission....

Evidently there is a programable option to not have the air brake come on if the cruise is on unless the brake is depressed.

Jeff