How much fuel per hour at idle?

[permx11]

Does any know how much fuel per hour our Duramax engines use? Trying to figure out how many mpg I am loosing during warm ups etc.

[Diesel Dragon]

Permx

I'm not sure about a Duramax but over the road trucks with 12.7, 14.7, and 16 liter motors use about 1 gallon per hour idiling. Not much if you ask me so I would imagine that the Duramax uses less than that so figure about $2.00 per hour on the high side for fuel. And dont forget to include wear and tear on the motor for just sitting there idiling.

Later Diesel Dragon :cool:

[chuntag95]

You could fill it to the neck. Move out of the way. Read for an hour. Pull back to the same pump and fill to the same level. Let us all know what you find out.
Chris

[Kennedy]

Calculated fuel rate will vary with ECT, engine load, and other factors, but as a rule:

8-10mm3/1000 strokes (cc's) at idle.

675 approx idle speed.

So we have 4 firing events per revolution on an 8 cylinder 4 stroke yielding 2700 firing events per minute. This should mean we use 2.7 x 10mm3 or 27 mm3/minute and 1620 mm3 or 1.6 liter/hr at idle.

This is how the factory mileage computer "guestimates" MPG by using MPH to get the result.

My math skills are limited, so someone with more time/better math skills please check my numbers and convert to US measure. I have air to chase...

[chuntag95]

Assuming the 10 mm3 of fuel per firing, I get 0.428 gal/hr at 675 rpm. The direct conversion of JK's 1.6 L/hr is .423 gal/hr. Now, if it is 10 mm3 per stroke and not per firing, then it is reduced by 4 or 0.107 gal/hr which does not sound or feel right based on mileage lost when I idle more. If I use the .107 gal/hr, assuming a 3 hour idle on the tank, it would drop me by 0.2 mpg and 0.8 mpg with the .428 number. 0.8 is more consistant with my winter mileage drop with increased idleing, as I am around 0.7 lower when it's cold. :cool: This is only an estimate (time, mgp, plus the other items JK mentioned) and based on my truck. Yours may vary.

[Kennedy]

10cc's per 1000 injection events, or .010cc/stroke

For comparison's sake, the engine HP tag rates the 300HP at 3100RPM at I believe 90mm3 fuel rate.

Placing the transmission in D or applying an exhaust brake will increase the engine load and also fuel demand...

[chuntag95]

I found the difference in our numbers. Rounding of the 1.62 L/hr to 1.6 L/hr. The final answer is "0.427959 gal/hr" :D

Now, multiply times nine for max Hp and it's 3.85 gal/hr. (I rounded to 2 decimal places to save on disk space) tongue.gif ;)

JK, Thanks for the clarification on what you meant with the original number. I hate to be unsure. BTW, where did you find those numbers?

Chris

[conradv]

With the amount of significant digits used, about the closest you can reliably say would be 0.4 gal/hr. ;)

[chuntag95]

conradv,
With the variation from truck to truck, fuel fill to fuel fill, driving styles, temperature, blah, blah, blah, I don't think you can even be that acurate. Something like 0.4 +/- 0.3 is about the best I would swear to. :D You know, like the weather forecast "cloudy to sunny, between -20 and 120 with a chance for precipitation". Of course, a weatherman is the only job you can be wrong 90% of the time and not get fired. ;) tongue.gif :rolleyes:

[Kennedy]

CC/1000 strokes is a std of measure used by injection pump mfr's.

The 8-10mm3 is an observed value when watching the Tech 2.