Fast idle on a cold Cummins diesel?

[Neal]

I've watched some start their coaches in the morning and go straight to fast idle. Raises an eye brow a little for me, is that really good for a cold engine? Seems I'd want to let it idle and get fluids flowing first, warm up, then go high idle if needed

Any opinions on fast idle on a cold engine or shortly after starting?

 

[JRS]

I'll go to fast idle after oil pressure buildup + 30-60 secs. Experienced diesel mechanic said to keep idling to a minimum.

 

[Rich W.]

Fast idle is still only around 1000rpm with no load so its harmless but I too would wait a few minutes before doing it if at all. I imagine they were just in a rush to air up, but I’m never in that much of a hurry. Maybe they think less idle time is better so they are doing it at a higher speed for a shorter time? Doesn’t make sense but ya never know.

 

[Rd1]

This is another misnomer now a days. You 'may' have noticed, when you first start your engine, if it iscool enough temps outside, the engine ECM hi-idles for a brief period of time and then drops down to regular idle. Thats all it needs.

With new engines and ECM, I don't see any use for hi-idle as Rich says. The ECM takes care of what needsto be done. The old diesels had to be hi-idled to keep thing inorder.

Even for stops, ie fuel, I let the engine idle for even as long as 30min or whatever. The regular idle helps to stabilizes the engine and transmission temp, the turbo, etc.. when the engine is turned off for that 10-30 min or so of stopping, some parts of the engine may stay warmer than others. To me, thats more concerning than letting it idle for long periods.

I do the same when reaching camp, it idles for a long time while I get things hooked-up. Likewise when leaving, it idles while I get things secured.

When traveling long distances, Itypically covered 5-8 hrs of driving. Before planned stop, I'd easeup for some period of time to let things cool of some, before hitting the exit. Same after getting back on the hwy, I''l keep ez depending on weather, etc, Till all warms up evenly, before hitting the cruising speed!

 

[JRS]

Mine doesn't high idle at first than drop down.
The experienced mid 30's mechanic who told me (he was a camper nearby) a couple times during our stay not to idle new diesels with the new emission systems for long periods of time and to keep idling to a minimum. He suggested fast idling when you have to idle. Also said it's one of the worst things you can do to these new engines which actually surprised me when he told me that....
IMHO, by the time you get off the hwy exit and to the campground office the engine has cooled off. I shut down when checking in.
To each his own

 

[MemoriesByTheMile]

Fast idle is part of the standard air brake test procedure, when testing that the compressor builds up the pressure between 2 different pressure points in less than a certain time.

There seems to be some variance between different tests, but the one we use we check that the pressure builds between 50 and 90, while using fast idle, in less than 3 minutes.

I will give the engine time to build oil pressure before fast idle, but that is typically less than 30 seconds.

What makes me raise my eyebrows is diesel engines idling more than 5 min when most manuals that I have read state they should not idle for more than a couple minutes — except when cooling down after leaving highway or heavy load use.

 

[Rich W.]

if you can ignore all the pop-ups and ads, this seems like a fairly balanced discussion on the topic:

What Is Diesel High Idle and When Should You Use It?

If you drive a diesel RV, you may be aware of diesel high idle (sometimes referred to as "fast idle"), and your rig may even have a high idle mode or

www.thervgeeks.com

 

[CaptainGizmo]

FWIW, these are the Standard protocols I’ve learned for the most extreme use…Fire engines and trucks. Our rigs were under the strict care of certified mechanics; Detroits, Cummins, and CATS.

- Engine heater to keep block and fluids warm
- Idle until pressures are built up before hit’n it
- After load, do not shut down immediately

Of course, we had hours of near idling; rarely using fast idle.

These diesels are beasts and will tolerate “constant RPM” running for days…just think of a generator!

This said, the DEF system keeps clean with HEAT. And in the middle of a REGEN, the procedure is to let idle for 45 minutes, it it’s not being driven.

So…Carry on…our “RV” usage is pretty weak-toast compared to what these engines can take.

 

[Rich W.]

Since this discussion began I’ve developed a few concerns as follows:

1. Soot build-up in the EGR
2. Cylinder wash
3. Varnishing of combustion chambers (I just found this one to add to the list)

I’ll continue researching all of the above. One thing I’m not concerned about is the DPF - having the ability to perform regens negates any concerns here.

The modern fire engines we operated idled for hours on scene as Captain Steve stated although we were also periodically advised against extended idling. But there are some major differences with those rigs: they were exempt from any emissions related derate functions, they had constant care by the city garage, any time we had an issue we could just swap into a reserve unit, and while they were in service for 12 years before rotating to reserve status, they never developed very high milage because we didn't travel that much in them - a few strike team trips around the state each year but primarily local response. Operators were never worried about long term impacts of idling. We might need to pay closer attention to the issue.

All that said, I won’t shut down at a fuel island, and while I’ve recently read some comments about idling while checking in to a park being “bad manners”, generally speaking the entrance of a park is far enough away from occupied campsites that the concern seems unwarranted. I’d rather wait until I’m parked for the day before shutting down, avoiding unnecessary starts and stops, and ensuring that I won’t be stuck somewhere I don’t want to spend the night (or longer).

But as I said, I’ll revisit all of this and I hope others will add their insights, practices, and experiences.

 

[jbh]

Generators and pumps are running at speed under load, not idling.