Fuel consumption at idle
Postmaster
Joined: Jun 2006
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From: Fulltime RVer
After the engine is up to operating temp it's less than 0.5 GPH at a 650 RPM idle in neutral without the A/C on. If you're in drive it can require as much as 1.0 GPH to idle depending on the tranny temp. For long stop lights shifting to neutral saves a little fuel!
Post Fiend
Joined: Jun 2006
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From: White Mnt's,New Hampshire
Postmaster
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From: Fulltime RVer
Here's how to calculate/estimate the answer. When idling in neutral at say 650 RPM the available FWHP is 0 HP because all of the piston combustion HP that's being produced by the reciprocating pistons is being consumed by friction loss, parasitic loss, and pumping loss.
If you had a 100% efficiency for converting the chemical ENERGY in summer blend #2 diesel fuel into piston combustion HP a 1 gph fuel flow would produce 51.1 HP. The actual conversion efficiency is about 65% so for a 0.5 gph flow this gives HP={(51.1)(0.65)(0.5)}=16.6 HP as the piston combustion HP required to overcome the above mentioned losses and maintain an idle at a 650 RPM.
Based on this 16.6 HP to idle at 650 RPM the HP required to crank the engine with the starter motor at 100 RPM is {16.6}{(100)/(650)}=2.55 HP which requires a {(2.55)(746)}=1.9 kW starter motor at 100% efficiency or a 2.4 kW starter motor at 80% efficiency which is consistent with the specs for the starter motors that I've seen.
After my C7 warms up to normal operating temperature my VMS 240 CL made by SilverLeaf Electronics, Inc... VMS 240 CL | SilverLeaf Electronics, Inc. ...indicates a 0.55 gph fuel flow when I'm idling in neutral at 700 RPM with the A/C off.
If you had a 100% efficiency for converting the chemical ENERGY in summer blend #2 diesel fuel into piston combustion HP a 1 gph fuel flow would produce 51.1 HP. The actual conversion efficiency is about 65% so for a 0.5 gph flow this gives HP={(51.1)(0.65)(0.5)}=16.6 HP as the piston combustion HP required to overcome the above mentioned losses and maintain an idle at a 650 RPM.
Based on this 16.6 HP to idle at 650 RPM the HP required to crank the engine with the starter motor at 100 RPM is {16.6}{(100)/(650)}=2.55 HP which requires a {(2.55)(746)}=1.9 kW starter motor at 100% efficiency or a 2.4 kW starter motor at 80% efficiency which is consistent with the specs for the starter motors that I've seen.
After my C7 warms up to normal operating temperature my VMS 240 CL made by SilverLeaf Electronics, Inc... VMS 240 CL | SilverLeaf Electronics, Inc. ...indicates a 0.55 gph fuel flow when I'm idling in neutral at 700 RPM with the A/C off.
Gone Fishin for Mark
Joined: Nov 2004
Posts: 1,354
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From: West of Houston
Hot danged iffin I don't miss Gene powerful bad. Good to see ya buddy.
The bottom line is that you don't want to leave the engine idling for too awful long or you will get wet stacking. Basically that means that all the fuel does.nt get burned and leaks by the rings and dilutes the crankcase oil.......or so I have read.
The bottom line is that you don't want to leave the engine idling for too awful long or you will get wet stacking. Basically that means that all the fuel does.nt get burned and leaks by the rings and dilutes the crankcase oil.......or so I have read.
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New User
Joined: Jun 2007
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Thanks guys! I was up camping last week near Truckee, CA and about froze my hiney off, so I fired up the pickup and thawed out and was curious how much the heat was costing me....
Thanks again!
Thanks again!
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Logistics Pro
Joined: Nov 2006
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From: Fallon,NV & Bainbridge OH
Three things; first, welcome to the site; second, you must be *ucking crazy to camp here this time of year (even though last weekend was nice) last night hit -10, and third you should have said something we could of had a beer. Next time through say something.
Postmaster
Joined: Jan 2004
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From: Kearney, Nebr
Wet stacking is not as big of problem as it used to be in those order diesels. Combustion temps usually stay up. I'd be worried more about low oil pressure during extended idle periods.
Kick on the high idle every now and then if you have it and you won't have a problem.
Kick on the high idle every now and then if you have it and you won't have a problem.
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New User
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Hey Dave-
You are right - it was WAY frickin' COLD! My mirror said it was 9....
I am up your way quite a bit, my home is in Rocklin but I have business interests in Reno and my son and I love the recreation (fishing, camping, quadin') all around your neck of the woods. My email is dukermeyer@hotmail.com - shoot me a message and I will try to give you a heads up when I am in town and I'll buy you a beer at Bar of America!
Look forward to it!
Duke
You are right - it was WAY frickin' COLD! My mirror said it was 9....
I am up your way quite a bit, my home is in Rocklin but I have business interests in Reno and my son and I love the recreation (fishing, camping, quadin') all around your neck of the woods. My email is dukermeyer@hotmail.com - shoot me a message and I will try to give you a heads up when I am in town and I'll buy you a beer at Bar of America!
Look forward to it!
Duke
Logistics Pro
Joined: Nov 2006
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From: Fallon,NV & Bainbridge OH
Duke, I will send you an e-mail.
Rick your signature says you want to go somewhere so put a small house on that trailer you haul Dodges on and head west. The beer and everything else is cold here in Truckee this time of year.
cold beer!
Rick your signature says you want to go somewhere so put a small house on that trailer you haul Dodges on and head west. The beer and everything else is cold here in Truckee this time of year.
cold beer!
Hook it, I'll pull it.
Joined: May 2007
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From: Grand Lake, La.
. It does sound like a great time. 
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jrockdiddy
1948 - 1956 F1, F100 & Larger F-Series Trucks
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Jul 2, 2015 10:01 AM
73, calculate, consumption, consumtion, diesel, freightliner, fuel, gas, idle, idling, leaf, m2, powerstroke, silver, truck
