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Fuel burned idling

Today I was looking at all of the values my ECM had using my Nexas code reader.  Coach has 61,1xx miles on it.  engine idling hours are 225. Fuel used idling is 400 gallons. So this comes out to 1.78 gallons per hour.  When I have the coach airing up I use high idle so that might explain some of it. It's amazing how many hours are used idling. 

I have not paid any attention to what the load is on the motor when in gear sitting at a light but going to pay attention next time out if I remember.

My diesel Yukon averages around 24 mpg.  so one hour idling in coach equals around 42 miles driving in Yukon.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Fuel burned idling and other thoughts!

Reply #1 –
So here in New York and many other areas Engine Idling, especially for Diesels is prohibited or restricted. So many pays attention to it. 
When I purchased my 2004 Tropi-Cal which was set for California, once the engine reached temperature it would shut off after 3 minutes idling. Back in New York we often have heavy traffic here. A few times it even shut off while in gear. I learned that if stopped to occasionally lift my foot off the brake pedal to reset that 3 minute timer. Eventually I was able to get the CAT dealer to disable that feature.

Looking at engine maintenance and overall life most people focus on mileage, even for vehicle value. Being experienced with industrial engines overall maintenance and wear are functions of hours and fuel consumed as that is an indication of load and contamination. Maintenance intervals for truck engines are often based on miles, hours, and fuel consumed. For example, you may see 10,000 miles, 1,000 hours, or 1,000 gallons fuel consumed. So, if you are getting only 8mpg, the 10,000-mile change becomes an 8,000-mile change.

From the vehicle value perspective, my 2022 Denali reached just over 41,000 miles as the engine reached 1,000 hours.  Averaging ~40 miles per hour. 250 hours idling could represent 10,000 miles of driving. While the engine is not working hard it is still wearing a bit and excessive idling does have some damaging effects. Those low mileage coaches are not always a deal.

I try to only idle for engine warm up and cool down. I try to avoid idling it just to run it. As for air buildup that should only take a couple of minutes. I don't fast idle although sometimes the engine will auto up the idle to get the alternator voltage up. The Foretravel doesn't do this often as the ECU does not see the low house battery voltage due to the diode block design. For coaches that use a relay to connect the house batteries you will see this more often. My routine is to start the engine, do one more walk around, confirm suspension is raised, test brakes, and then go, driving gently until I see the temp gauge rise. Off highway Inlet it idle for a few minutes to let the turbo cool and let some of that heat soak dissipate. Pulling in for fuel, go out back, check the auto trans fluid level, then shut it down. Pump fuel, then check engine oil level and coolant. Then start up and get out the way.
Dennis Haynes
Bohemia NY
2008 Nimbus 342 SE Carlyle
Build #6475
Motorcade #19148

Re: Fuel burned idling

Reply #2 –
I wonder if the ecm considers the engine is idling when rolling without touching the throttle?  Such as pulling in or out of a campsite?
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Fuel burned idling

Reply #3 –
I found this while searching for the answer

Quote
I emailed Cummins support and asked this question. Here's the response:

"Thank you for contacting Cummins. The resolution to your inquiry, Support Request from cummins.com - A Cummins product/service, is as follows:
Low idle setting in the ecm itself is what the ecm uses as a rpm number to trigger idle time. Usually its set at 700rpm factory so anything below that is considered idle time regardless of moving or not."

Star4900, that's right in line with your post.

How are Engine Idle Hours logged in the ECM on the truck? | TruckersReport.co...
1991 U300 Side Aisle 6V92 Silver #3897
2004 U320 40' #6246

Re: Fuel burned idling

Reply #4 –
Not directly related ecm idle hours, but Nebraska Tractor Test Lab has lots of info going way back if you are interested in fuel use at various loads.  Here are a few with engines used in RVs:
15L https://tractortestlab.unl.edu/documents/CaseIHSteiger_530Quad.pdf
10.8L https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=3076&context=tractormuseumlit
8.3L https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=3070&context=tractormuseumlit
Farm tractor engines are usually set at a lower power level since they were designed to run @ WOT under full load all day long. (This is not necessarily the case with more recent computerized engine and variable transmission controls.)

Dave and Kelli
1997 U295 40' Build #5188 CSGI
1995 U240 36' Build #4621 SBID-SOLD
2006 Jeep Wrangler Rubicon

Re: Fuel burned idling

Reply #5 –
I was never one to idle a diesel engine needlessly but looking back to the late 60's and into the 80's I also recall that in certain weather seasons a trucker, me included would start the engine when we left and many times would only turn off the engine to check the oil for an entire week. We had to for a place to sleep. I always felt that an hours idle could be an hour of going down the road as far as engine wear and fuel used. Point being we put millions of miles on those engines and I don't recall ever hearing a mechanic say this one fell because of excess idle time. Now it sounds like I don't mind ideling one but all I'm saying is that for the newbies if you have to idle your engine for an extended time not to worry because it will still start and run tomorrow and likely for the duration of your owning it and the next owner as well. Meanwhile I will still be turning my key to the left when situation allows. As far as the topic of fuel burned at idle, I always allowed a gallon per hour and it could have been north of that.
Dub McBride 1996 270

Re: Fuel burned idling

Reply #6 –
Looking back I got off topic from what Turbojack started without meaning to. I had a new owner ask me last trip how much idle time does it take to harm his engine. I couldn't answer that so all I could say in good conscience is that within reason he would not hurt the engine. Sorry about that Turbo, just making a point for new diesel owners and as of late we have a number.
Dub McBride 1996 270

Re: Fuel burned idling

Reply #7 –
Quote from: Dub –
Point being we put millions of miles on those engines and I don't recall ever hearing a mechanic say this one fell because of excess idle time.

Dub,

Not sure it is reasonable to equate the occasional idle time on an OTR truck that will then be pulling 80,000 pounds down the road (and therefore easily gets rid of the moisture produced while idling) with a motorhome that is only occasionally driven hard.

The worse internal rust I ever saw on a coach I inspected what an owner who proudly told me/prospective buyer that he absolutely started the engine weekly and idled it for half an hour.  Shining a light into the valve cover/oil fill looked like the ferrous metal parts had been dipped in salt water.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel burned idling

Reply #8 –
I have owned three class 8 tractors and operated them in very cold winters in South Dakota & Wyoming. So lots of idling during the cold months. I also had my oil lab tested at EVERY 10,000 mile oil change.  Which equated to every month for me. There was no difference in the lab test results between the summer (very low idle time)vs winter (much higher idle time) oil changes.

However, i always highly recommend to folks that they absolutely do not idle a diesel engine just to exercise it while in storage. A diesel engine should only be started if one is going to 'use' it.
Jerry & Nona and Kimeru the cat that thinks she's a dog
1998 36' WTFE U320  #5314 Motorcade #17711
USAF 1975-1995
2019 Subaru Crosstrek 'toad'
2003 Subaru Legacy touring car
jerry Fincher | Flickr