Fuel Consumption GPH

[Pete Judd]

Used HP vs fuel is very easy to figure out, and there are formulas out there, My little Yanmar, uses (under Load) about 1/3 of a gallon an hour, with the 5 ft brush hog, or the 5 ft finish mower. My 46 foot 16 ton sailboat with a 60 hp 4 cyl diesel, runs at about 1/3 per hour as well at 6 Kts speed. If I push up the speed to 7 Kts. At 7 Kts. will use .75 gallons per hour, and at 7.8 Kts, will be burning about 1.3 gallons per hour. The load is the key, not engine rpm. You can only get so much of a gallon of diesel.

But that said, some tractors are better than others, as gearbox, and engines can make a difference.

 

[pak7819]

Back in the day when I was still in the business the design criteria was 1/2 pound of fuel per horsepower hour. Kind of like outboard motors where fuel consumption in GPH at WOT = rated HP X 10%. Rule of thumb to get you into the ball park.

Opti-Mist: Is it coincidence that your reference to an outboard fuel consumption rate and your handle name (Opti,...max) might be related to a well known marine manufacturer in Fond du lac, WI?

Regarding "rule of thumb" design considerations, that is always at WOT under load, correct? Using 7 lbs for 1 gallon of deisel, 1/2 gallon = .071 lbs.

.071lbs x 40hp = 2.84 GPH,...if I'm using your "rule of thumb" correctly...

 

[jenkinsph]

Less confusing would be .5#'s x 40hp=20lbs/hour or 20/7=2.85 gph.

Off topic everytime I compare the Optimax to a more expensive Verado the Optimax seems to burn less fuel.

 

[Baby Grand]

285 hours 159 gal <> .56 gal/hr

 

[rd_macgregor]

There may be a confounding factor here. Is everybody using tractor clock elapsed time? I thought many (most?) tractor clocks actually recorded elapsed time corrected for rpm...essentially they are really recording total revolutions divided by some "standard" rev factor (usually in the neighborhood of 2500 rpm).
Or, have I misunderstood how this works?
BOB

 

[Jerry/MT]

The hour meters are correct at one rpm. But for the precision available for this discussion, I doubt that it makes a big difference. You'd have to measure the fuel with a high degree of accuracy and fill the tank to precisiely the same level each time and then adjust the time, know the lower heating value of the fuel, accesory loads, etc to get a high degree of accuracy and I doubt anybody in this discussion is doing that.

The numbers quoted here, at best , are probably within +/-5-10 % of the real answer but more likely ~+/-20%. So if you "measure " 0.5 gph, the truth is more likely somewhere betwee 0.4 and 0.6 gph. I worked in the aircraft industry and it cost us dearly to be able to measure fuel flow at better than 1% accuracy. (We actually calibrated our fuel meters with a large part of the actual fuel delivery system.)

Fuel usage is very dependent on load. To get a good idea of this look at the Nebraska Test data for any tractor. The BSFC (Brake Specific Fuel Consumption, lbs /hp-hr or sometimes gallons per hp-hr ) is generally presented graphically as a function of rpm at full load .(With the advent of the EPA ,"Full load" is usually determined by a visible absence of smoke now. In the old days it was a determined by a certain optical "smoke number".) It is also presented graphically as a function of load with rpm as a parameter. When you quote the fuel usage at rpm, fuel flow is all over the place because rpm does mean load.

As an example, an older Cat diesel has a BSFC of 0.61 @ 1000 rpm and 50 hp load and 0.45 @ 1000 rpm and 100 hp load (Ref: "Internal Combustion Engines" by Obert). So the fuel flow at 50 hp load is 24.4 lbs/hr versus 45 lbs/hr at 100 hp at a constant 1000 rpm.The fuel flow at constant rpm was over 1.8 greater for a doubling of the load in this example.

So unless you know the load it's hard to make meaningful comparisons of fuel usage.

 

[MHarryE]

Older tractors had hourmeters that read hours at X rpm, but every newer tractor I have seen has a digital electric meter connected through an oil pressure switch so it records hours when the switch is on and oil pressure is greater than a specific value, usually 5 psi or 0.3 bar.

 

[Jerry/MT]

Older tractors had hourmeters that read hours at X rpm, but every newer tractor I have seen has a digital electric meter connected through an oil pressure switch so it records hours when the switch is on and oil pressure is greater than a specific value, usually 5 psi or 0.3 bar.

Not "every new tractor". I have A 2007 New Holland and I have a mechanical tach/hourmeter.
And not "every" old tractor used mechanical clocks. I had a 1960 John Deere 435 and that used an hourmeter that used the oil pressure switch to start and stop the clock.

The point I was trying to make is that with all the other inaccuracies in determining fuel usage, the error due to the mechanical clock was insignificant for the purposes of this discussion.

 

[Chilly807]

Not "every new tractor". I have A 2007 New Holland and I have a mechanical tach/hourmeter.

My 2009 L3400 is the same, has a mechanical tach and hourmeter. It's surprisingly accurate, I was doing extended runs bush-hogging a field last summer at 540 PTO speed and tried checking the elapsed time against my watch.

I'd rather have the electronic one, to be honest. A lot of my running time is below 540 PTO speed. One solution for maintenance purposes is to change fluids more often, there's never any harm in that other than a minor dent in the wallet.

My "guess" at fuel consumption rates, and it IS a guess, is based on the number of hours I get before adding a fixed amount of fuel, usually pretty close to 5 gallons. Bush hogging, which is about 60% of full load under most of my conditions, yields a run time of about 5-7 hours before I add fuel.

Sean

 

[JDgreen227]

I started a thread in the "Fuels and oils" forum where I revealed my total fuel costs for both my vehicles and JD 4210 for the year. My calculations show my Yanmar 73 Cubic inch engine has consumed .623 gph for this year...about 85% of my operating hours are running a 60 inch MMM deck at 2300 rpm, 5% is snow removal, and the remaining 10% is brush clearing, rock moving, etc. Pretty happy with the overall economy, especially so because diesel rarely goes under $4 a gallon here.