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Diesel vs. Gas engines on ZTRs

Discussion in 'Lawn Mowing' started by gbparn, May 4, 2011.

  1. Mark Oomkes

    Mark Oomkes LawnSite Fanatic
    Posts: 11,251

    The Lazer had one.

    The others were diesels. I don't think Kaw makes a gasser big enough to run those mowers. Or a fuel tank.
     
  2. hackitdown

    hackitdown LawnSite Silver Member
    Posts: 2,486

    I tend to agree, the savings on fuel is small. I average 350 hrs each per year on two mowers. Based on a 40% reduction on my fuel consumption, I would save about $400 per year (per mower) on fuel by switching to diesel. So unless a diesel mower is more productive, and saves on labor costs, I don't think I can justify the up front expense of a diesel.

    All things being equal (other than the engine), how much more does a diesel upgrade cost on a mower?
     
  3. hackitdown

    hackitdown LawnSite Silver Member
    Posts: 2,486

    Got it. I think the guy with the leaks was talking about a Kawi L/C engine.
     
  4. Mark Oomkes

    Mark Oomkes LawnSite Fanatic
    Posts: 11,251

    I understood it to mean any and all L\C engines.
     
  5. heather lawn sp

    heather lawn sp LawnSite Senior Member
    Posts: 681

    Being rude and countering your question with a question, how big a mower?

    Kubota ZD221 $10,368
    Kubota ZG222 $7,754

    . . . TW's assumption was for 3 mowers should be 2 out fronts are only auxilliary, and check his assumptions are with/without the marked diesel price.The 9's are 72 inch and 60 inch, 132 inches total. The gas are 54 & 60 inch 114 inches total. The 9's have 15% more forward speed. Statistically speaking 33% more area per hour. Last computation done was diesel at .9 gallon per hour.

    So 33% more area
    81% fuel cost
    & 81 % fuel consumption

    diesel over gas up to 2 x productivity

    I'll verify 2010 marked diesel fuel consumption
     
  6. heather lawn sp

    heather lawn sp LawnSite Senior Member
    Posts: 681

    I lied

    diesel fuel consumption was 4.72 L/hr or 1.24 US gallon per hour


    So
    33% more area
    81% fuel cost
    112% fuel consumption

    fuel cost and consumption virtually cancel out (90%), same cost per hour leaving 33% more area per hour. Bear in mind the 997 cost about twice as much as the ZG 221. ($7,000 spread over 7 year of life)

    997 $4.61/hr
    665/757 $5.085/hr
    The test becomes:

    Can you save $1,000 or more a year in fuel to pay for the mower?

    Our $3700 diesel bill would increase by $1,233 for gas

    For us this works

    One further wrinkle, note both our older gas engines were swapped out at around 2000 hours, the diesels are still around at 2500 hours

    Question: Does anybody have the gas consumption of 72 inch Z-turn mower?
     
    Last edited: May 18, 2011
  7. TWerner

    TWerner LawnSite Member
    Posts: 80

    Sorry for the errors. I did state my assumptions and say I needed more information.

    I'm a little confused. You put 112% on fuel consumption, but previously said you were burning more gallons of gas in less hours than you were diesel. How did you come up with 112% fuel consumption? Was the gallons per week wrong? If not, then:

    400hours/25weeks is 16hrs/week/mower->32 hours/week total 50gallons/32hours is about 1.6gph
    250hours/25weeks is 10hrs/week/mower->20hours/week total. 53gallons/20hours is 2.65gph

    Again, I get about 40% less gph.

    Given the diesels are bigger and still moving faster, a diesel on a smaller deck mower might save even more GPH. I think $4 fuel savings/hour of mowing is a lot. Even $2/hour is enough to make the diesel pay for itself quickly if you mow large properties. If your mower runs 15 hours a week and rides on a trailer the rest of the time, diesel doesn't make much sense because you'll pay more to haul the extra weight.
     
  8. hackitdown

    hackitdown LawnSite Silver Member
    Posts: 2,486

    Ok, it sounds like the cost to upgrade to a diesel on a 54" mower is $2,600. If I can save $400 per year on fuel (I am running 52" mowers...close enough comparison for me), the break even point is 6.5 years at my 350 hrs per year, or at about 2300 hrs.

    I have to think that a gas mower with 2300 hrs is at or past the end of it's engine life. Assuming a diesel will go a lot more hours, then the payoff is really big after the break-even point. A gas engine swap is a couple of thousand dollars, and presumably the diesel will just keep running.

    Or am I missing something?
     
  9. TWerner

    TWerner LawnSite Member
    Posts: 80

    We need to clarify the GPH with Heather Lawn SP.

    If the burn rate is 40% less, or a gallon less per hour on a 72" mower, then you save about $4/hour. That's the price of a gallon a gas plus the lower cost of a gallon of ag diesel. If you pay more for diesel, figure you'd save about $3.5/hour.

    So $1200 to 1400/year in gas. Probably a bit less on a 52/54" mower, but still significant.

    I'm not clear on the numbers from yet.
    Sorry,
    Todd
     
  10. hackitdown

    hackitdown LawnSite Silver Member
    Posts: 2,486

    I think it would be less on the smaller 52/54" mowers, since I'm only burning 1 gph of gas. Factoring in the higher cost of diesel, and the assumed 40% lower consumption, I would save about $1.15 per hour.

    I will be mowing more hours this year (and in the future I hope), so the break-even date could be sooner. And if a diesel is somehow more productive, saving labor $$. As someone said, more hours, and bigger mowers make the best case for diesel.

    Are they cheaper to maintain?
     

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