Cummins 5.9 fuel burn at idle: (Did an experiment)

[JEstes]

I've only been a member here for a short time, but I've learned alot since I've been here. So, I thought it was time for me to contribute something to the group.



I've noticed some posts lately about people asking how much the 5. 9 burns at idle. If you look at the overhead console, it seems like it burns a ton. On the other hand, it is a diesel so idle fuel burn should be next to nothing.



I searched all over the internet and even called a friend of mine who works for Cummins. Neither he nor I could find any real info on the subject. He even asked a few engineers, but they didn't have any real numbers for the 5. 9. They could tell him all about idle fuel burn in semi-trucks though.



So, I decided to do a little experiment. After a fairly long drive to get the truck up to full operating temp, I stopped by a truck stop and filled up a portable fuel jug and topped the truck off. I made the short drive home, and parked the truck, but left it running. I topped it off again with the fuel jug, and started my timer. I let it idle for 1 hour, and shut it off. I then topped off to the same level, but I measured how much went in. After one hour of idling, it burned slightly under 1/4 of a gallon. The outside temp was 50, and the engine temp never dropped below the 190 it normally runs.



There was one funny thing I noticed. The overhead console didn't show any change in MPG. It's only had 140 miles on it since it was last reset, so it shouldn't take much to make it change. Maybe someone can chime in here, but the only thing I can think of is that I had the e-brake on. Maybe with the e-brake on, the computer doesn't calculate MPG?



By the way, my friend asked one of the Cummins engineers about extended idling, and he said it shouldn't hurt it unless it's really cold outside or the engine is already cold.



Sorry for the long-winded post, but I figured I'd tell the entire procedure in case anybody was interested.

 

[rbattelle]

How did you make sure you "topped it off to the same level"? Fill it until you can see it in the filler neck?



It would be interesting to put a flow meter in the fuel system and measure direct. I was going to do this at one time, but later decided the money for the flow meter would be better spent elsewhere.



Ryan

 

[betterthanstock]

Our 5. 9 should burn about half of the big rig engines.

What numbers do you have for the big guys?

 

[Bob4x4]

How did you make sure you "topped it off to the same level"? Fill it until you can see it in the filler neck?



It would be interesting to put a flow meter in the fuel system and measure direct. I was going to do this at one time, but later decided the money for the flow meter would be better spent elsewhere.



Ryan

You would also have to measure the return flow and subtract to get the correct amount.



Bob

 

[hammersley]

10 Min rule ----

I was told a long time ago that unless you're going to be longer than 10 min - leave it idle as the fuel to start is more than consumed in 10 min at idle... . don't know if it's true or not... . BUT I do know the absolute WORST FUEL MILEAGE you can get is at Idle as the MPG is ZERO!!!!

 

[Ross]

I've run a Volvo VNL with a Cummins N-14 @ 515 hp/1650 tq as a toter for my big horsetrailer for a couple years. At high idle (900 rpm), the computer showed about 0. 8 gph. I'm sure it would be about 0. 5 at 600 rpm, but the truck's parameters were set to shut down at 5 minutes of idle on low idle. Fleet owners don't allow long idle periods at low idle because they tend to increase cylinder wear due to cold (relatively) cylinder temperatures, which in turn lead to washing down the cylinder wall. When I bought the truck, I had the opportunity to reset this high/low idle parameter, but left it alone, since I thought if the fleets run that way, it ought to be a good idea for me too.

 

[TBartlett1]

Sounds about right. In the 90's I worked in an engineering lab with cummins engines so I knew some Cummins engineers and I also bought my new 1990 CTD so I wanted al the information I could find. They sent me fuel maps, repair manuals and other information which I still have but can't fine at this moment and the fuel consumption was approx 1 liter per hour for the original 160hp. The lowest BSFC was . 34 lbs/hphr @ peak torque for this engine.

 

[JEstes]

How did you make sure you "topped it off to the same level"? Fill it until you can see it in the filler neck?



It would be interesting to put a flow meter in the fuel system and measure direct. I was going to do this at one time, but later decided the money for the flow meter would be better spent elsewhere.



Ryan

Easy. I just filled it up to about 1 inch below the fuel cap. I figured short of putting fuel flow meters in it, this was the only real way I could measure idle fuel burn.



I know this isn't exactly the discovery of the century, but I sometimes need to use the truck as a source of 12V power. It's not a hard load, but it is continuous and will draw a deep cycle marine battery down in about an hour. I just wanted to see how much fuel I was going to burn by leaving the truck running while doing this.

 

[steved]

SO if you were stranded with even 20 gallons in the tank, you could theoretically idle for 80 hours... not bad to know these days... especially after what just happened last week in PA (stranded motorists).



steved

 

[jjdiesel]

The e-brake would place a load on the engine, a small one sure, but I wonder how much fuel that would account for?

 

[JEstes]

The e-brake would place a load on the engine, a small one sure, but I wonder how much fuel that would account for?

When I said e-brake I meant emergency brake, not the exhaust brake. This one is an automatic, so no exhaust brake for me... .

 

[Buffalo]

Interesting information. I would have expected the engine to have used more fuel, than that.



Thanks for the post.



Joe F. (Buffalo)

 

[CarneyJ]

awsome post! Very interesting! I take it that it was on the truck that you have posted as your signature? The 2003?

 

[nickleinonen]

that sounds about right for idle fuel use for our isb's. . the engine i have at work [16v645 (10320cid) emd's] idle at about 3 gph. . they stay running all winter long [most of the time idling]

 

[JEstes]

awsome post! Very interesting! I take it that it was on the truck that you have posted as your signature? The 2003?

Yup! That was the '03. I can't imagine any of the other 3rd gen 5. 9's being much different. The new ULSD might have a tiny impact, but at idle it shouldn't make much of a difference.

 

[Vaughn MacKenzie]

the engine i have at work [16v645 (10320cid) emd's] idle at about 3 gph. . they stay running all winter long [most of the time idling]

I was told that too, and it was because RR companies use plain water in the cooling systems for whatever reason (probably costs a fortune for that much coolant).

 

[JEstes]

That's what I have been told too. I read on here someplace that those things have nearly 300 gallons of coolant, so they leave them running since diesel is cheaper than antifreeze.

 

[nickleinonen]

yep, straight water with a corrosion treatment compound mixed in [some look pink, some look green] and 300 gallons on the larger units is about right [and oil is about 300 gallons too]

 

[Vaughn MacKenzie]

It's only a matter of time before the enviros start compaining about idling locomotives! LOL

 

[JEstes]

It's only a matter of time before the enviros start compaining about idling locomotives! LOL

They already do... . Some states have anti-idling laws for semis, but I think most of the rail roads have gotten around it. Cummins has designed a small diesel powered generator that semis can use in place of idling the engine. It's supposed to keep the oil/coolant warm and provide power for the heat/air in the cab.