I was curious-I have the two alternators on the truck and use them to charge the batteries in the camper. So how many hours per gallon idling do these trucks get?

I bet you could idle the truck on a full tank for at least a day.

i've HEARD 4 gallons for 8 hours.

The tow guys like Rick know, they will be able to answer.

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I've heard about .5 to .75 gal per hour at idle.

My scangauge reads fuel use in gal/hr. An idling warmed up duramax in neutral/park no AC on uses 0.2-.03 gal/hr. (about 1 quart/hr). Put it in drive and it goes up about 0.1gal/hr. A good assumption is between 0.3 and 0.5 gal/hr idling and running the alternator.

If you want to use the alternators to charge your camper batteries and they are well discharged you probably want to use high idle to get enough alternator current to quickly charge them. A single battery probably can be charged pretty quick at idle. A couple of deep discharge golf cart batteries can take an initial charge of 60-80 amps pretty easily, don't know if a dual alternator can get that much current at idle.

Even at high idle I'll bet your less than 1gal/hr.

Agreeing with the above:

At idle, according to EFILive, I'm at about 5 mm3 main and 1 mm3 pilot. That equates to right about 1 qt/hr. It calculated to 0.936 L/hr.

You can double that figure if the engine is not warmed up, and triple it if the engine is real cold.

So, warm, in park = 4 hours per gallon.

Agreeing with the above:

At idle, according to EFILive, I'm at about 5 mm3 main and 1 mm3 pilot. That equates to right about 1 qt/hr. It calculated to 0.936 L/hr.

You can double that figure if the engine is not warmed up, and triple it if the engine is real cold.

So, warm, in park = 4 hours per gallon.

cit, if you load up the alterators, creating drag, will it be bumping up that rate a touch to compensate?

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I think a cautionary note is worthwhile (although we are really just noodling fuel consumption at this point) on long periods of idle. The owner's manual does not recommend it. I don't think I'd willingly subject my truck to it. It seems like it may also be a causitive factor in some of Problem Child's issues with his engine as he idled for long times to run an invertor for his camper. I suspect that long periods of idle can result in poor splash oiling to the wrist pin bearings as well as other issues.

I just pulled a bass boat out to AZ and I had to sleep in truck because of trolling motor, depth finder being gone in AM. Anyway I used about 4 gallons in 9 hours. When I got back on the road the truck smoked like a MF for 1/2 mile I guess from oil build up in the turbo. Scared the sh*t out of me. I thought the trailer tires were locking up.

I just pulled a bass boat out to AZ and I had to sleep in truck because of trolling motor, depth finder being gone in AM. Anyway I used about 4 gallons in 9 hours. When I got back on the road the truck smoked like a MF for 1/2 mile I guess from oil build up in the turbo. Scared the sh*t out of me. I thought the trailer tires were locking up.

You think the PCV moved a crapload of oil in there and then when you took off if started blowing it out of the intact tract?

I wasn't familiar with Idle_Chatter's post above either (what's an owners manual?? :confused: ), makes me wonder if all these "attention getters" that leave their trucks idling everywhere know about that. :rolleyes:

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i have left my truck idling for 12 hrs at at time and yes it will smoke like a fright train pulling a grade for about 2 miles but then it clears up and is gone.i have 4350 hours on my duramax and have not had any problems associated with idling.as far as how much it uses idling less than a gallon an hr at stock idle,but sometimes as much as 1.3 gal hr on high idle.

cit, if you load up the alterators, creating drag, will it be bumping up that rate a touch to compensate?

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In theory, yes, the fueling rate will go up with any extra load. A/C adds about 20% (based on my observations of 1 more mm3)..more if it's real hot outside.

Trans in drive doubles it. Seems that cold oil really can increase it also.

As for 2 alternators under load? No data here, a guess would be maybe 20% more.

I honestly don't think that extended idling is bad for anything AS LONG AS you don't dead idle--high idle is the ticket. I've had to let my truck high idle for 8 hours + when it was -30 °F here, and I didn't have any smoke as a result once I drove off.

High idle kicks the oil pressure up considerably, and I don't see any harm in it. OTR trucks high idle 8 hours a day year round and are expected to run 500,000 + miles in fleet service.

Problem Child suffers lots of problems I don't. :)

How are you high idling the truck?

We tap into the ECM and use the PTO function.

See Max Power's thread under the "DIY" section of the site.