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

[Fish]

The owners manuals of both my 2018 Cummins dually pickup with 6.7 cummins and my 2007 Monaco Camelot with the 8.8L cummins say to avoid extended idle. If I need to idle my Camelot I bump it up to 1100-1200 rpm with the cruise control.
I do leave the Camelot running while fueling. I figure that coasting into my campsite qualifies for a good enough turbo cool down.

My new neighbor here at the resort has a 2500 ram with the cummins 6.7 and he idles the hell out of it. He lets it run for 5-10 minutes before he drives away. I don't know why and I'm not going to get into his business. I haven't heard so much diesel idle since I was working at the refinery, everyone at the rv park had diesels, it was like 10 degrees outside and everyone was warming them up some to leave for work.

I also didn't get into his business about his floppy awning being out flapping in the stiff winds we've had here lately, yesterday I noticed his awning wadded up and at the road for the trash guys and only a metal frame remaining.

 

[Underboss]

At Gaffney, I asked about this. They said no extended idling. If you must idle, bring the rpms up. I cannot remember but I believe it has to do with DEF

 

[Kevin D Pem]

• Nov 14, 2023

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"I said I wasn’t going to do this but there is some good info here. These are from various diesel forums and the third bullet is from a dodge pick-up forum, but there is some good information to ponder (and some minor contradictions) and it might answer some questions." Rich

So I wonder the sanity of searching forums for solid facts! I know I don't!!! If facts are needed manufacturers websites, or authoritative sites are the only place I expect anything other than social interaction!!!

 

[Joe Dutchstar]

Even asking Company reps will get generic answers unless you are very specific as to make/model/application.
Incomplete combustion would be a Big issue allowing cylinder wash down and oil dilution.

According to the Spartan chassis rep at the seminar in Tampa, time limits on lubricates are very important. The additives are subject to oxidation and water contamination from air humidity which degrades the additive package.
Cold starts and excess idling are hard on additives. He explained that the Cummins engines are designed for a million miles. The expectation is high milage I.e. 100,000 a year.
So most RVs will follow the time limit on maintenance due to the low usage rates. Sitting in storage or at a campsite subjects the lubricants to oxidation and contaminants from moisture or corrosion.

Consequently we change fluids that require a change every annual visit for maintenance regardless of mileage. Or at the stated mileage if we exceed the recommended limit during the year.

 

[ARD]

Has anyone found a definitive answer/definition to is considered excessive idling? How long is considered excessive? 5 mins, 10 mins, 30 mins?

 

[Joe Dutchstar]

In my opinion since there are so many variations in equipment and application, it is best to refer to the specific Manuals supplied with your RV.
If that topic is not addressed call engine mfg support.

Granted this is not the fun discussion path but will give you a defensible documented position should things go wrong.

 

[Racklefratz]

At Gaffney, I asked about this. They said no extended idling. If you must idle, bring the rpms up. I cannot remember but I believe it has to do with DEF

Agree. Our 2012 Tiffin has the Cummins ISL 450hp in it, and extended idling definitely asks for issues.

While at the Tiffin factory service center, we had modifications to the tag axle suspension air pressure work done, which required long periods of engine idling to keep the system aired up.

When we left the facility, we were greeted with immediate DPF warnings that only cleared after we have been at road speeds for a while. The extended idling resulted in clear messages from the system that it didn't like it.

 

[Racklefratz]

If facts are needed manufacturers websites, or authoritative sites are the only place I expect anything other than social interaction!!!

Of course. Forums are fine if the question has to do with others' opinions or preferences. For factual info on operation and/or maintenance, I rely on the OEM or their designated representatives.

 

[AbdRahim]

Well, if someone would provide the funding, I would do the research to answer the question scientifically. I suppose we could use DP’s in the middle of the price and engine size range. Let’s see, I would need 30-40 of them and funds for the fuel. Any takers? You all can pool your funds.

 

[Joe Dutchstar]

Thought I’d ask Grok 2 the question, spoiler alert
, nothing new here

“Extended idling can indeed be harmful to diesel engines for several reasons:

1. **Fuel Dilution**: Idling for long periods can lead to fuel dilution of the engine oil. Unburned fuel can seep into the oil, reducing its lubricating properties and potentially causing wear and tear on engine parts.

2. **Carbon Buildup**: Diesel engines can accumulate carbon deposits in the combustion chamber, on injectors, and in the exhaust system when idling for too long. This can lead to reduced performance and efficiency over time.

3. **Increased Maintenance**: The wear and carbon buildup can necessitate more frequent oil changes and maintenance to keep the engine in good condition.

4. **Regeneration Issues**: Modern diesel engines with Diesel Particulate Filters (DPFs) require periodic regeneration to burn off soot. Idling doesn't provide the conditions for effective regeneration, which can lead to DPF-related problems.

5. **Waste of Fuel**: Idling consumes fuel without providing any significant benefit, leading to unnecessary operational costs.

6. **Environmental Impact**: Extended idling contributes to unnecessary emissions, negatively impacting the environment.

However, there are some scenarios where short idling might be necessary, like warming up the engine in very cold weather to ensure all fluids are at optimal operating temperatures or for systems like the DPF to initiate regeneration. But generally, for most modern diesel engines:

- **Warm-up**: A brief warm-up period is often sufficient; extended idling isn't needed.
- **Heating**: If the vehicle is used for heating or cooling (like in construction sites), alternatives like block heaters or auxiliary power units are more efficient and less harmful to the engine.

Best practice is to limit idling time as much as possible, ideally not exceeding more than 5 minutes unless absolutely necessary. If you're in a situation where idling can't be avoided, consider using technology or methods to reduce its impact on the engine.”

 

[team bradfield]

So you shut it off in heavy traffic/construction or accident?

 

[Texas Clodhopper]

So you shut it off in heavy traffic/construction or accident?

If I think I will be stopped for 10-15 minutes, yes, I turn the motor off and usually get up and walk around and get a snack or drink.

Since the Cummins manual states "Don't idle excessively", and they don't define excessively I err on the side of caution.

 

[Neal]

Since the DEF head crisis I only shut off when I need to so I leave it running while fueling now. I typically shut down when checking into a CG for noise and courtesy to the campers. I don't like surprises after engine start.

 

[MemoriesByTheMile]

So you shut it off in heavy traffic/construction or accident?

If we aren’t moving for a few minutes, yes, we will always shutdown the drive engine. Will then use the gen and house A/C as needed.

 

[MemoriesByTheMile]

Since the DEF head crisis I only shut off when I need to so I leave it running while fueling now. I typically shut down when checking into a CG for noise and courtesy to the campers. I don't like surprises after engine start.

I never thought about this before, would DEF failures only show up immediately after a startup? Or is there a higher incidence rate triggered by startup?