Community Forums

SC182 · 06-22-2022, 11:09 AM

Never thought about this until Diesel hit $5+. Does the use of engine braking cause a significant change in MPG? I'd imagine it would not when trips are long and on the interstate. How about backroads and in town driving? Would the additional fuel burned ever equal a brake drum/pad replacement?

edge68474 · 06-22-2022, 11:20 AM

I know what I think, but I will wait to see what a real mechanic has to say.
Is this in regards to a Jake brake or an Exhaust brake?
I will follow this thread.

Alan_Hepburn · 06-22-2022, 11:22 AM

Quote:

Originally Posted by SC182

Never thought about this until Diesel hit $5+. Does the use of engine braking cause a significant change in MPG? I'd imagine it would not when trips are long and on the interstate. How about backroads and in town driving? Would the additional fuel burned ever equal a brake drum/pad replacement?

I'm not familiar with the current technology but I would suspect that the ECM might shut down the injectors when the engine brake is engaged.

scotttkd · 06-22-2022, 11:26 AM

Other forums posting on this as well. The general consensus I have read is engine braking turned on when not actually needed (downhills) is no different than dragging a brake when not needed and will affect mpg. How much is a matter for experts with more knowledge than me. As for me and mine, I am turning off the engine braking unless I'm on extended downhills.

Old-Biscuit · 06-22-2022, 11:26 AM

Slight decrease in overall mpg because you loose the 'coasting' affect when you take your foot off accelerator pedal

BUT.....increase in service brake longevity!!

edge68474 · 06-22-2022, 11:35 AM

Hi gang. Not knowing your guy's Rv, what type of engine brake do you guys have?? Thank you.
My thinking is, and I have drove truck but like I said, I am not a mechanic, if you aren't giving it throttle, it doesn't use any more fuel.
I really like a Jake Brake, at least the older ones.

Max Headroom · 06-22-2022, 11:46 AM

Quote:

Originally Posted by scotttkd

Other forums posting on this as well. The general consensus I have read is engine braking turned on when not actually needed (downhills) is no different than dragging a brake when not needed and will affect mpg. How much is a matter for experts with more knowledge than me. As for me and mine, I am turning off the engine braking unless I'm on extended downhills.

I have a Jake in my coach. I leave it on all the time. It has a separate foot pedal to kick it in. It does not activate automatically. I can coast if I want to. The ECU is also programmed to cut it off at about 5-10mph, so you can Jake your way to a stoplight, and only use the service brake for the last little bit.

I think you can have the ECU programmed to auto activate any time you lift off the gas. And some builders may go for this option instead of installing the foot pedal. If that is your set-up, it would be non-optimal IMO, and I'd get the foot pedal and have the ECU reprogrammed.

BTW I love the Jake. It has a two position setting. HI is all 6 cylinders, LOW is 3 cylinders. Mostly run it on HI, and it is quite effective. Has about the same deceleration rate as a 'normal' brake application. If you need a panic stop it's nice to have both the Jake and the service brake. In fact its so effective that on long moderate grades I sometimes have to switch to LOW because it will slow the coach too much, and it's off, on, off, on... On LOW you can just kick it in and maintain your speed on a lot of downgrades.

ArtJoyce · 06-22-2022, 11:47 AM

We lose about ..5 mpg if I leave it on. I now turn on the brake when needed heavy traffic

wolfe10 · 06-22-2022, 11:53 AM

The answer is IT DEPENDS.

On flat ground, not so much.

In rolling hills, quite a lot. Instead of coasting down the small downgrade and building a little speed, you apply the BRAKES (doesn't matter if service brakes, exhaust brake or engine compression brake). Then on the next uphill, instead of trading some of the extra speed for elevation, you very quickly go to WOT to climb the next hi.

And, if in power mode vs economy mode, you would probably quickly drop a gear so WOT at higher RPM.

I would never want to eliminate my favorite "gear"-- COASTING!

YOUR CHOICE.

KenZ71 · 06-22-2022, 12:05 PM

Seem to have a more controlled slowdown with the engine break.

In light traffic I'll take the engine break off but that is also to be more moderate. By default I leave it on.

If 0.5 mpg has that much difference bigger issues to worry about.

n2zon · 06-22-2022, 01:12 PM

Quote:

Originally Posted by Alan_Hepburn

I'm not familiar with the current technology but I would suspect that the ECM might shut down the injectors when the engine brake is engaged.

This is exactly what it does on our Cummins common rail injection system.

wolfe10 · 06-22-2022, 01:15 PM

Correct. With throttle closed, no fuel is injected. Makes no difference if coasting or with engine brake on.

dbircky · 06-22-2022, 01:19 PM

I think the key word is BRAKE. Anytime you convert motion into heat, you are not maximizing fuel mileage. Doesn’t matter which kind of brake it is.

Gary RVRoamer · 06-22-2022, 02:29 PM

Quote:

Originally Posted by dbircky

I think the key word is BRAKE. Anytime you convert motion into heat, you are not maximizing fuel mileage. Doesn’t matter which kind of brake it is.

Right, so if you brake when it's not needed, you are wasting fuel (what wolfe10 said).

If you merely turn off the jake or exhaust brake and use the service brakes instead, there is no difference in mpg. But if you brake when you could have coasted, you end up using fuel when you could have used inertia instead.