Diesel vs. Gas engines on ZTRs

[Mark Oomkes]

Originally Posted by hackitdown

Your lawn mowers.

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.

[hackitdown]

Originally Posted by TWerner

400/250 is 1.6. So if I read that correctly, your 3 diesels are running 60% more hours total, but burning 6% less gallons of fuel than your 3 gas mowers? That comes to almost exactly 41% less fuel burned.

I assumed the diesel and gas mowers were the same size and mow at the same speed. It's more than a 41% savings if the diesels cut more per hour.

Using $3.50/gallon to be conservative, and 50 gallons/week on gasoline, that's $175/week on gasoline versus $105/week on diesel. Buying ag diesel might make the savings a bit more, say $75, but even so, if you only save $25 a week on a mower running 400 hours a year, it will take a while for a diesel to pay for itself.

For a better analysis, I'd need the hours per week per mower.
Then I can plug in the numbers to show how much you save per hour on fuel. Again, I am assuming your diesels and the gas mowers cut the same area per hour.

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?

[hackitdown]

Originally Posted by Mark Oomkes

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.

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

[Mark Oomkes]

Originally Posted by hackitdown

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

I understood it to mean any and all L\C engines.

[heather lawn sp]

Originally Posted by hackitdown

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?

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

[heather lawn sp]

Originally Posted by heather lawn sp

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

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?

[TWerner]

Originally Posted by heather lawn sp

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

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.

[hackitdown]

Originally Posted by heather lawn sp

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

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?

[TWerner]

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

[hackitdown]

Originally Posted by TWerner

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

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?