Exhaust brake usage, can it cause an issue

[gweedo295]

Good morning, I recently had my exhaust manifold surfaced and gasket replaced on my 07 ISL400 and we are about to take out again.

I was reading through some older threads regarding the use of the exhaust brake and it causing more heat which creates a lot more pressure on the gasket leading to failure. When mine failed (which I posted on IRV2 when it happened) I noticed the exhaust noise was much more louder with the brake on.

Perhaps I am not using it the way it is designed for. So with that said my questions are:

1. Do you always have your exhaust brake on?

2. Should it be off while traveling down the road or does it matter

3. Do you use it in city traffic

4. What RPM do you maintain while descending a hill with it on

I know sometimes I hit 22-2300 RPM and the engine is roaring, I can't help but think this may be a huge contributing factor to the exhaust manifold failure, but I couldn't say for certain. I read where guys have had the repair reoccur and I'm trying to avoid this.

Opinions on its use are all over the place on the streets, so this is why I turn to the experts in the know at IRV2. I have only had the rig for two years now and still learning. Any suggestions would be appreciated.

Thanks, Pat

[CountryB]

There are two types of brake used - one is a "compression or engine brake" (a.k.a Jake Brake) and the other is an "exhaust brake" (a.k.a. PAC brake).

The compression brake, opens the exhaust valves to dump engine compression, and would not add any additional stress or heat to the exhaust. When it opens it dumps the compression from the cylinder and the cylinder does not fire so there is no added heat to exhaust. https://youtu.be/HkfjCJClWVA

The exhaust brake is a flap in the exhaust that closes to build up back pressure in the cylinders and exhaust manifold. This could build up heat (and pressure) in the exhaust manifold.

So an "exhaust brake" works by increasing pressure - and a "compression engine brake" works by reducing pressure.

However, the engine is designed for either style and you should not need to worry about engine component failure for either style.

For Jake Brake:
1) I don't use it unless I'm in the mountains or area with steep hills.
2) I would leave it off for normal driving (Interstate highways - not in mountain zones) when I 'm also using Cruise Control.
3) If city driving has some steep hills, I would turn it on.
4) should try to maintain the rpm where peak torque is made (around 1800-2100 on most big diesels). An engine brakes needs high rpm to work best.

[AKOne]

Pat good questions. Like Mike said, the engines are designed for these systems. Since these systems are to assist in braking, I use mine regardless of the drive situation. However, I do not leave it on even though the PAC will disengage below a preset RPM. I expect that is why there is an on and off switched. I too, would like to know the answer to your RPM question.

[slowmachine]

Since the injectors are flowing little or no fuel while the exhaust brake is in use, the engine is really acting as an enormous air pump, running relatively low-temperature air into the exhaust. Despite the “blockage” created by the exhaust brake, I’d bet that it is cooling the manifold, especially at the higher RPMs needed for effective braking.

[Ivylog]

There is not a temp increase using an exhaust or Jake brake...cracking Cummins exhaust manifold is a know problem.
Monaco was pretty good about ordering the ISL with a true Jake Brake...hence the loud noise from releasing the compressed air. The more rpms the more braking you get...no load max rpms is higher than the power rpms so 2300 is OK.
I like a left foot switch to activate letting you coast without feathering the throttle.

[96 Wideglide]

Originally Posted by Ivylog

Monaco was pretty good about ordering the ISL with a true Jake Brake...

Well, as the owner of a Monaco Coach, with an ISL and exhaust brake ..... I would have to disagree with this!

[AKOne]

Originally Posted by Ivylog

No load max rpms is higher than the power rpms so 2300 is OK.

Is there a stated "no load max RPM" anywhere?

[vito.a]

Most of the exhaust manifold/gasket issues are caused by multiple heat cycles. When these engines are installed in trucks they tend to run them for extended periods and in an RV they are repeatedly heat cycled.

[CountryB]

my CAT C13 engine manual says this:

[96 Wideglide]

Originally Posted by AKOne

Is there a stated "no load max RPM" anywhere?

Yes!
Should be listed in your engine manual specs. My 2007 built 400ISL is 2650 rpm.

[Old Scout]

Agree--ISLs of that era have known issues with cracking exhaust manifolds....rather than the PAC brake, I subscribe to the view that the exhaust manifolds of that era were pretty weak to begin with. So with the turbo and piping hung off the manifold there is a lot of stress. But the real issue, in my opinion, is a finite number of heating and cooling cycles--I lost my first manifold about 5 yrs in to ownership. No problems with the replacement over the last ten years. My strategy is to minimize heat/cool cycles--so my ISL runs all day, unless I am going to have a long rest stop. No quick stops and I let it run during refueling.....

[79cvx20]

I agree with old scout . I have had two ISC 8.3 Cummins engines in 38 to 40 foot motorhomes . First one was a 1992 and the second one was a 2002 ISC 8.3 350 horse. After a lot of studying because my first one was warped I found it is a very common problem . The 1992 model ran virtually perfectly for the first 400 miles after I bought it . Then I found that the engine had been overheated and I had to rebuild it because of many overheated/broken parts . It broke the piston rings on two pistons and even the springs in 2 injector nozzles. After the first 400 miles after I bought it and before the rebuild it blew raw fuel out the tailpipe. It hasn't used more than 2 qts or leaked any oil at all since 2 years ago. The man that bought it drives it hard with an over 7,000 pound box trailer in tow.
When I was searching for a newer motorhome I found a few cracked manifolds on Monacos with Cummins . I have been a mechanic for over 56 years. I also know that cycling cool to hot constantly is a big problem with both the gasket leaking and manifold cracking . That is probably the reason they went to a two piece manifold in later years . Since a lot of the bolts are relatively hard to get to, torquing is often not properly done. The anti seize compound required is not only to keep the bolts from rusting in place but is required for proper torquing them . In my opinion they should also be retorqued after the engine has been warmed up which is almost impossible on most. I often get as much as three quarters to one turn extra when I tested the difference between antiseized and dry bolts. On the first of my engines both the head surface of the exhaust and the exhaust manifold were extremely warped. And had been so hot that when I torqued it one of the ears broke off of the head. I had to devise an unorthodox way of clamping it in place with some machine work but it is still working perfectly two years later. The rest of the exhaust system also needs to be properly supported and torqued. I have been getting online parts catalogs and engine service manuals from this Cummins website for years. It is completely open to the public.
https://quickserve.cummins.com/info/index.html
It is great information. It goes by serial number of engine. Just wish I could find the same for my Cummins Onan Kubota diesel generator. The correct and exactly the same parts I bought from Kubota were about half the price of Cummins. I have since found that you can't even get a bolt from Cummins or any other Cummins supplier without the serial number. They don't care anything about what year, size or anything else.

[gweedo295]

Wow thank you everyone for the responses. well even here there are differing opinions and that is good. Not sure what type of brake I have, I know I can feather the pedal for partial or full braking.

A couple responses indicated the possibility of the heat up and cool down could be a contributing factor and it makes sense. SO, if you make short stops, lets say a rest stop and you leave the rig running, do you raise the idle via the cruise control to 1100 RPM or do you leave it at idle?

I believe Cummins says not to leave at idle speed after about two minutes, allowing the oil pressure to level. How long is it okay to idle or idle at the higher RPM? When I have it parked, I start it once a month and run it at high idle for 15-minutes. Is this okay to do? or is it too long of a period of time.

What do you do during the down times?

Thnx again!

[CountryB]

This is from Adept Ape (CAT engine) video - but applies to all diesels:

https://www.youtube.com/watch?v=hvfMal5fReA