Question Is extended idle really bad for a Cummins diesel? Fact or myth?

[Neal]

In the world of RV's we sure get a lot of opinions and I like "fact checking" or learning more and vetting out some of these myths. In my other post about fast idle some points came up about extended idle. In the spirit of DEF head failures a lot of us now probably keep our engines running vs. engine cycles which can be good and bad as we'll likely discuss below. I personally keep my engine running while fueling now where in the past I did not. Campgrounds I typically do shut off and I am the one that raised the topic here and other forums about being respectful of the noise. While some campground offices are well clear of campers, some are close to campsites and being aware and respectful is a good thing, so I will typically shut down at check-in unless AC is required for fido, etc.

So let's chat about extended idle. Is it really bad? Says who? How long have diesel engine owners been doing this? Any ramifications?

So about that soot build up, idle or not, wouldn't the system detect these levels and start a regen even if at idle? The RPM would come up likely to fast idle at best for a regen, but my thought is even when idle, the system will manage itself, which is my opinion and not fact based at all. Curious what others think?

Are we "fear tactic'ing" ourselves to shut down when maybe it's not really something to be concerned about?

 

[Kevin D Pem]

My guess is the climate change freaks have more to do with the idle issue! Than does harm. Remember when the truckers idled all night keeping truck stops out of towns? Then Remember legislation requiring them to shut down?

Truckers idled because it didn't matter, to reduce larger repair bills!

That said, I was reluctant to weigh in on this! Honestly I would rather not listen to the noise, but the fumes cause me issues. Gassers are not much different, but engine size has allot to do with the volume of fumes. People with Gassers have no excuse for being inconsiderate, I hope this post will prove people with diesels don't have an excuse either!!!

 

[sheridany]

In the prevost world there’s a fast idle rocker switch and it’s recommended to use it if idling for more than a couple of minutes and or extending-retracting slides.

 

[jaydee325]

A good read:

https://info.ornl.gov/sites/publications/files/pub61263.pdf

 

[MemoriesByTheMile]

This should be a good discussion, using reputable sources to understand what is correct.
We only idle after heavy loads for 3 minutes per the instructions in our Freightliner operator manual, do not idle when fueling or at camp office, etc unless it is still in that 3-5 minute cooldown after heavy load.

But I don’t know if that instruction in the Freightliner manual is due to concern of engine damage due to lower lubrication, concern over cooler cylinder temps leading to incomplete combustion which yields higher emissions, concern of “fuel wash” shortening the life of the engine oil, many state laws banning idling more than 5 min, or ???

I have found it tough to find data backed info on this. Very easy to find fear-backed anecdotal “evidence”.

 

[jbh]

A corollary question is what applies to a '90s-era diesel as opposed to a modern diesel. I don't need to be concerned with DEF or DPF, so what is the concern with idling 30 minutes or so?

 

[Scooterfan]

Although virtually all of my experience is with large marine diesel engines, I'm thinking this logic still applies (and this is ALL pre- DEF) Once a diesel engine is started is should not be turned off until it has reached operating "Idle" temperature(s). After being run it should not be turned off until operating temperature(s) have dropped to normal "Idle" temperature. Idling in between these states is simply burning fuel and adding operating hours. Now if you are idling to charge battery banks, run pumps for fish holds, etc then keep her running. The new motors sound too complicated for me. Blessings

 

[sanda]

My guess is the climate change freaks have more to do with the idle issue! Than does harm. Remember when the truckers idled all night keeping truck stops out of towns? Then Remember legislation requiring them to shut down?

Truckers idled because it didn't matter, to reduce larger repair bills!

That said, I was reluctant to weigh in on this! Honestly I would rather not listen to the noise, but the fumes cause me issues. Gassers are not much different, but engine size has allot to do with the volume of fumes. People with Gassers have no excuse for being inconsiderate, I hope this post will prove people with diesels don't have an excuse either!!!

Pre-def diesels needed to idle to cool the turbo. 5 minutes usually was sufficient. I agree with your post concerning diesels idling in campgrounds for long periods as not to expose fellow campers to the noise and odors.
I also don't understand why an RV manufacturer would suggest starting the engine to pull in the slides. On all of my trailers with slides as long as you had proper voltage at the batteries this wouldn't be necessary.

 

[ARD]

I also don't understand why an RV manufacturer would suggest starting the engine to pull in the slides

I have to air up before bringing in my slides. In my DS, I would air up, turn engine off, bring in slides and start the engine again to leave. Of course, back then I had 2018 Newmar DS and so had no choice, but to turn the engine off to bring the slides in once I brought the coach to ride height.

In my LA, that is not the case and makes no sense to turn the engine on/off and I cannot tell you the reason why the tech thinks leaving the engine running other than the power for the heavy hydraulic FWS. Perhaps that is why Newmar made it so one can run the slides out with the engine running. I will ask when I return for service it there is another reason.

As far as when I arrive somewhere, I am already aired up and find it strange that people would be so intolerant of an idling engine for 5-10 minutes so I can connect to power, water and put jack pads down prior to putting my slides out. Lawd, there are so many other things to get upset about. I will not be shamed - talking to you @Neal

 

[Rich W.]

I have my own ideas about this but I spent some time today reading a lot of good, bad, and contradictory information on the subject (what the internet is great for) to confirm or modify my methods and procedures. I got a lot out of the process, but rather than regurgitate what I found, I went back to the source: The Cummins operator‘s manual for my engine.

You can find your’s here with your 8 digit ESN: https://www.cummins.com/support/manuals .

You’ll probably find the same info I did but I expect there are some differences between the various displacements and model years.

The following are excerpts from the pertinent sections and pretty much sum up the situation (note the slight ambiguity in the Aftertreatment warm up section):

Extended Idle
Do not operate the engine at low idle for long periods with engine coolant temperature below the minimum specification in Maintenance Specifications (Section V). This can result in the following:

• Fuel dilution of the lubricating oil
• Carbon buildup in the cylinder
• Cylinder head valve sticking
• Reduced performance.

Do not operate internal combustion engines at low idle speed for extended periods of time. This operating condition can lead to poor engine performance. The idle shutdown feature, available on most Cummins® engines, can be programmed to shut the engine down after a period of low idle speed operation with no driver activity. A flashing warning lamp will inform the driver of an impending shutdown. If an engine mustidle for an extended period of time, operate at fast idle (1000 rpm or greater). The Power Take-Off (PTO) feature, available on most Cummins® engines, can be programmed to adjust engine speed with the use of OEM switches to pre-programmed set points.

Aftertreatment Warm-up

The aftertreatment warm up function is used to help prevent the buildup of water condensation in the aftertreatment system during extended idle operation.

After approximately one hour of engine idle operation, the engine speed will increase to 1000 to 1100 rpm, and remain at this speed for 10 minutes. During this time, the aftertreatment system is warmed up enough to evaporate any water that has condensed in the system.

The aftertreatment warm up function can be stopped by depressing the throttle, clutch, or brake pedal. If the engine continues to idle, the aftertreatment warm up function will try again to raise the idle speed until the aftertreatment temperatures are suitable.

Engine Shutdown

Failure to follow the correct shutdown procedure can result in damage to the turbocharger, if equipped, and shorten the turbocharger life.

Allow the engine to idle 3 to 5 minutes before shutting the engine off after a full-load operation. This process allows adequate cool down of pistons, cylinders, bearings, and turbocharger, if equipped.