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

[mr.wilson]

Hey, I have a question: Was your truck at high idle for the entire hour? I know anytime I leave mine for more than ten minutes or so it will automaticaly jump up to the high idle.

C

 

[JEstes]

No, it was at a normal idle. Mine won't ever go into high idle unless it's really cold outside, or it just started. It would be interesting to see how much fuel it burned at high idle though.

 

[DZink24]

JEstes, are you inside my head?!?

I have been considering doing the exact same thing that you have described. I have been curious to know myself. Considering how the readout overhead drops like a rock, it seems like it burns a ton.



The way you did it, is the best possible way I can think of to measure, although there is one major "control" issue to deal with. Namely, since it is such a small amout that gets used, it is imperative that the tank gets filled to the exact same point each time. (Less margin of error, as opposed to driving say, 600 miles on 30 gallons).

Due to the weird shape of our tanks, this is very tough. In the past, I have filled, topped off w/ a 5G jug, right to the top, spilling. But I know that there is still air in the bubble at the extreme top of our tanks. (enter tank vent mod )

I will do this test shortly, 1,000 RPM. I will most likely use a Pyrex measuring cup, be certain that I am parked on level ground, and try to eliminate any air in the fuel. I'll post results.

This may be something that the more of us that do it, the more numbers we will have to get a better average.

 

[DerekW]

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.

Hey dude all you had to do was consult me before you wasted your fuel money. I have a 2004. 5. when I am on long road trips or have somewhere to be in the morning thats really super important I used to shower and leave the house. fuel up at the truck stop 30 miles away and sleep with the big rigs. I burn 1/4 tank in an 8 hours worth of sleep with the a/c on high, running lights on, cell phone on charge (i am trying to say low engine load). my truck was straight pipe when doing this and banks 6 gun with speedloader set on level 2 (timing). I also would have to be at a shop bright in early when it opened to pick up parts so I would shower up put on fresh clothes and ride all the way to the shop a few hours away then park it. wake up early pick up the parts and drive across state and install them on a customers vehicle at the shop I worked at. Many other reasons such as when I moved back in with the family I would get kicked out of the house when it was my moms time of the month and such I would four wheel to my fav spot hangout spot and fall spend the night. It was actually one of the tests I did while on a overnight test drive with the truck (overnight test drive put on 600 miles, me and my bro crashed in it 4 the night, almost got stuck 4 wheeling in sand, hooked up to a big trailer and all, brought it back muddy the dodge dealer detailed it while I signed the paperwork).



But anyways my truck burns 1/4 tank (32 gallon tank at the time on straight diesel) in 8 hours worth of rest with engine running for climate control. If somebody out there does consider pulling over to catch a few z's while driving long distance leave engine running set a/c on cold for to feel even more refreshed when they awake compared to sleeping at whatever temp. Also if you decide to spend the night in the truck (whether you break down or whatever) always have some soda (or bottled water) to use to brush your teeth in the morning. just some of my experience.

 

[DerekW]

oh and if someone was to catch even a few z's while on the road cuz they are falling asleep behind the wheel. I highly reccomend you pick a good place to catch some z's where the 2 sets of flashing blue lights with two mag lights in your eyes while beating on the glass don't wake you. I personally am tired of that bullcrap. Me and my boss decided that I need to buy a big *** race trailer to haul around so I can crash without the unappreciated awakening when Its been a long day at work and I cant make the long ride home. normally it is 2 cops with nothing better to do while waiting for dunkin donuts to get a fresh batch in.

 

[DerekW]

Hey, I have a question: Was your truck at high idle for the entire hour? I know anytime I leave mine for more than ten minutes or so it will automaticaly jump up to the high idle.



C

on mine in the summer time it wont kick into high idle when extended idling. I have noticed my truck will kick into high idle when the engine is too hot while in neutral or to engine is too cold while in neutral. But regardly I would bump the throttle if you have the chance up to 1,000 for a few seconds. Normally the factory high idle kicks in for only 10 minutes when conditions are right. It normally takes between 2 and 10 minutes for it to decide to kick into high idle also.

 

[DerekW]

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.

my problem is I need a/c in the summer time at night

 

[JEstes]

my problem is I need a/c in the summer time at night

I know that feeling. I'm one of those people that sleeps better as it gets colder. Slightly above freezing works for me. :-laf I don't know if those semi truck anti-idling laws would apply to us though.







Dzink, let us know how yours goes! It will be interesting to see how 1000 RPM does. I don't have the cruise control high idle enabled yet, so I can't do that one unless it's pretty cold and the truck idles up on it's own.



Mine does have the fuel tank vent mod, but I know exactly what you mean about the air in the tank. I had to add close to a half a gallon just to cover the 2 minute drive from when I first filled up... .

 

[DZink24]

I know that feeling. I'm one of those people that sleeps better as it gets colder. Slightly above freezing works for me. :-laf I don't know if those semi truck anti-idling laws would apply to us though.







Dzink, let us know how yours goes! It will be interesting to see how 1000 RPM does. I don't have the cruise control high idle enabled yet, so I can't do that one unless it's pretty cold and the truck idles up on it's own.



Mine does have the fuel tank vent mod, but I know exactly what you mean about the air in the tank. I had to add close to a half a gallon just to cover the 2 minute drive from when I first filled up... .

Yeah, that sloshing fuel will screw up any scientific results we try to secure real fast. Why cant they just make a regular shaped fuel tank!! Enough with the oblong lumps and stuff!



DerekW- 1/4 tank in only 8 hours?? I am no diesel mechanic, but that seems like an awful lot for just having a minor electrical load.

 

[betterthanstock]

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.

How can diesel be cheaper than antifreeze?

At $1. 80/gal x 3 gal/hr x24 hr x 365 days = $ 47,304. 00 / year !!!!



You can buy enough coolant for 100 locomotives (at 50/50 mix) and replace it every year.



They don't shut them off because of extreme difficulty in starting a large, cold diesel engine. Some engines have too small a radiator to efficiently cool with antifreeze. Water cools better than glycol.



Some locomotives are starting to add small diesels to run and keep coolant hot, and the batteries charged, while turning off the main engine. It's a matter of antiquated equipment, and difficulty of retrofitting. Emissions laws are forcing them more and more to do something about it, and the cost of fuel will too.