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  #1  
Old 06-17-2008, 12:49 PM
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OM617 fuel consumption question

I'd like to know how much fuel a typical OM617 will consume within a time period and different throttle settings.
For example at idle, at full throttle/no load and at full throttle/full load.
Gallons/hour, liters/minute, pints/week, any unit will be good.

Trying to get approximate values, I'm researching the possibility to build a MPG gauge and would like to know the consumption so I can order fuel flow meters with a suitable range.

I could go out and measure this with a measuring glass but it's difficult to measure the consumption with full load (moving at full speed uphill with a jar of diesel between your knees? ..)
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  #2  
Old 06-17-2008, 12:58 PM
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It depends largely on how you measure it. If you loop the return then you only need to measure the input, from the tank, and the flow will be relatively small. The other way would be to use two flow meters, one for each the source and return lines, and subtract the difference. The problem with the first is that any air that gets into the pump will get trapped there with no return to the tank. The problem with the second method is that the flow rates that you measure will be much larger than the fuel usage, combine that with two flow meters instead of one, and the accuracy of the measurement will not be very good.

In short, the type of flow meter you get will depend on how you plan on measuring consumption. Eg. case 1: One low rate flowmeter, case 2: two high rate flowmeters.
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  #3  
Old 06-17-2008, 01:03 PM
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hmmmmm.....

Sounds like you just need to know the maximum fuel flow for the engine. If you can find the maximum delivery of the injector you can calculate the maximum fuel flow by multiplying the number of cylinders times the rpm divided by two.

From there you can divide the drive shaft rpm by the fuel flow rate and scale it to get your fuel consumption.
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  #4  
Old 06-17-2008, 01:04 PM
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Two flow meters is the way I intend to go (to get away from the air trap). Are you saying I can't get an accurate reading on fuel consumption if I subtract the return from the supply?
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1966 Mercedes Benz 230S with OM617.912, automatic. Disk brakes from W108
1983 Mercedes Benz 300TD grey, OM617.912 and 5-speed manual
1983 Mercedes Benz 300TD blue 7-seater, OM617.912 and 5-speed manual
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  #5  
Old 06-18-2008, 06:34 PM
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If anyone's interested having this for reference, here's my measurements:

Engine: OM617.910

Idle (warm engine): 0.0183L/minute (1.098L/hour)
About 20% throttle (warm engine): 0.0396L/min (2.374L/H)

Both measurements are 10-minute averages.
I would like to get the full-throttle consumption but with no load it isn't possible, and driving around with a jar of diesel between my knees wasn't an option..

IF the injection throttle increase is linear a full throttle application would give something like 12L/hour but I find that a bit on the low side so I don't think I can extrapolate the 20%-figure onto a credible 100%-value.
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1983 Mercedes Benz 300TD grey, OM617.912 and 5-speed manual
1983 Mercedes Benz 300TD blue 7-seater, OM617.912 and 5-speed manual
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  #6  
Old 05-24-2009, 05:18 PM
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This is good information. I do wonder what the fuel flow rate would be at constant highway speeds... Doable, on a flat road as the bucket wouldn't spill any diesel, right
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  #7  
Old 05-24-2009, 10:14 PM
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Quote:
Originally Posted by Johtotahti View Post
This is good information. I do wonder what the fuel flow rate would be at constant highway speeds...
At a constant 60 mph with minimal grades, the consumption is approx. 8L/hr...........depending on engine condition.

My guess on the consumption at maximum load and maximum rpm's would be approx. 56L/hr.
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  #8  
Old 05-24-2009, 10:50 PM
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Quote:
Originally Posted by Brian Carlton View Post
At a constant 60 mph with minimal grades, the consumption is approx. 8L/hr...........depending on engine condition.

My guess on the consumption at maximum load and maximum rpm's would be approx. 56L/hr.
56L/hr? Thats a ton....14 gallons. So you're saying that if you ran the car flat out at 115mph, max rpms and max load......you'd use 14 gallons of diesel to drive 115 miles? That's only 8.2 miles per gallon. Even when I did a long trip speeding at around 85-95mph I still got nearly 20mpg. I doubt it'd be that high...

By that calculation you'd clean out the tank and be coasting to the side of the road if you drove flat out for barely 170 miles....I doubt that. I bet the lowest you could get would be around 15-16mpg....
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  #9  
Old 05-25-2009, 12:18 AM
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Quote:
Originally Posted by pawoSD View Post
56L/hr? Thats a ton....14 gallons. So you're saying that if you ran the car flat out at 115mph, max rpms and max load......you'd use 14 gallons of diesel to drive 115 miles? That's only 8.2 miles per gallon. Even when I did a long trip speeding at around 85-95mph I still got nearly 20mpg. I doubt it'd be that high...

By that calculation you'd clean out the tank and be coasting to the side of the road if you drove flat out for barely 170 miles....I doubt that. I bet the lowest you could get would be around 15-16mpg....
Might be a bit less............but, there's a big difference between 85 mph and 110 mph...........the horsepower required is more than double..........and, therefore, the fuel required is more than double.
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  #10  
Old 05-25-2009, 12:46 AM
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Quote:
Originally Posted by Brian Carlton View Post
Might be a bit less............but, there's a big difference between 85 mph and 110 mph...........the horsepower required is more than double..........and, therefore, the fuel required is more than double.
Perhaps.....I wonder how long the motor could run putting out maximum horsepower like that.....I'd imagine it exponentially takes "lifespan hours" out of it.....
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  #11  
Old 05-25-2009, 01:43 AM
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The C111-III averaged 17.6mpg traveling 186mph at 3400rpm with 230hp.

Its pretty difficult to get a 300D/CD/TD/SD below 20mpg without poor tuning or a fuel leak. My 300D got 25.8mpg on its first tank, with a leaking delivery valve, a bad injection pump and me not going easy with the throttle.

Last edited by ForcedInduction; 05-25-2009 at 01:50 AM.
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  #12  
Old 05-25-2009, 03:19 AM
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The last time I got 20mpg highway I was grossing ~6,000 lbs and traveling 60-65 nonstop.
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  #13  
Old 05-25-2009, 10:43 AM
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Quote:
Originally Posted by pawoSD View Post
Perhaps.....I wonder how long the motor could run putting out maximum horsepower like that.....I'd imagine it exponentially takes "lifespan hours" out of it.....
Yep........it's time at those power levels is definitely limited. I'd doubt that you'd get more than 250 hours under those conditions.
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  #14  
Old 05-25-2009, 10:51 AM
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Originally Posted by Brian Carlton View Post
Yep........it's time at those power levels is definitely limited. I'd doubt that you'd get more than 250 hours under those conditions.
Although Mercedes managed to get over 60 hours of continuous higher than stock output from two of theirs. Even longer if you consider the time not counted by the third car that hit the hedgehog.
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  #15  
Old 05-25-2009, 12:20 PM
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Sounds to me like there are still too many variable to get a definitive answer...

Won't those numbers change with temps, altitudes, tune up condition, etc?
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