Kubota Gas vs Kubota Diesel engine option

[plowhog]

I am considering the purchase of a Ventrac 4500, but am undecided on engine option. I've narrowed it to either Kubota gas or diesel. My expected use is summertime mowing/brush hogging.

My inclination is diesel, for two reasons. One is fewer problems with fuel, such as if the unit is parked for a while while the gas ages. With a diesel unit I am more comfortable letting the machine sit for a longer period of inactivity than with gas. Such as over the winter. The other reason is perceived longer life in a diesel engine. I am not as sure about that, as Kubota supposedly uses very similar blocks for both the gas and diesel engines, and each runs at 3600rpm.

The factory tells their dealers to push the gas engine, which is more powerful at 32hp. The diesel is only 25hp and is not turbocharged. I don't have a practical way to test the diesel power for my needs, but from an earlier test drive of a gas unit plus reports from diesel owners it should be fine.

Again, I am leaning toward diesel but don't like going against what the factory recommends, which is the Kubota gas engine. Have I missed anything to consider between the two engines?

 

[MountainBuck]

My dealer also suggested the Kubota gas but I went with the Kawasaki instead because of the angle at which it can operate.

I was told that the Kubota gas engine has to be choked at every start, even when warm.

I'm curious why you would not consider the Kawasaki engine?

 

[CobyRupert]

My :2cents:
As far as longevity, I believe diesel wins hands-down. It seems that with diesel longevity, the turbo is the weak link and one just has to be prepared to replace them at some point. (Unless it has no turbo!) Yes turbo boost power, fuel efficiency, emissions, power, etc..; but IMHO, turbos are a trade off.

As far as 32hp (gas) vs. 25hp (diesel): They probably measure that 32 hp with a wide open throttle (or close to). It's a question of do you want horsepower, or torque?
The torque the gas engine produces (and horsepower) may drop off significantly when not wide open. The torque a diesel engine can produce typically does not drop off as sharply as a gas engine at lower rpms.
Remember that horsepower= torque x rpm. "To make more power an engine needs to generate more torque, operate at higher rpm, or both." So a low torque motor at high rpms (gas) can be advertised to have more "horsepower" than a diesel motor, that although it has more torque over a wider range of rpms, it has a lesser (top end - maximum) rpm, and lesser "horsepower".
Basically: Using horsepower in a gas vs. diesel comparison is comparing apples to oranges.

 

[plowhog]

The Kubota diesel has 42 ft/lb of torque, the Kubota gas has 51.

I focused on these two engines because the sales person recommended them. I did a Ventrac test drive with the Kawasaki engine and it was fine, although I did bog it slightly going up a steep slope at high speed cutting tall weeds. A very slight reduction in throttle fixed that.

The Kawasaki is unique in that it can operate continuously on slopes instead of a duty cycle. My guess is that I don't need that although it would be nice to have. I have enough mowing where I could mow a slope area for a while, then something flatter, etc.

Regarding longevity, someone told me that diesels achieve that by operating at lower rpm's. But in this case, both the gas and diesel Kubota engines operate at 3,600 rpm. So I don't know how that affects reliability?

 

[CobyRupert]

51 ft-lbs (gas) vs. 42 ft-lbs (diesel).
Interesting. It seems like they make diesel and gassers w/ closer and closer characteristics. However, it's likely these are peak numbers reached at a particular rpm. A graph of how torque varies over the operating range of rpms is a more clearer picture.
Some say diesel last longer because they're built stronger (heavier), run cooler (fuel is more efficient: more work / less heat) and diesel is a good lubricant.
Do you get cold temperatures there? If so, will you need to start Ventrac?

 

[plowhog]

20F is typical low temp in winter, and not that often. I've seen it down to 10 but that was only once.

The Kubota gas is model WG972-GL, 962cc that is bifuel ready for propane as well. The diesel is model D902, 898cc. Both three cylinder, both liquid cooled.

I periodically start up all the unused equipment over the winter. It's quite a few gas engines to feed, fuel, and worry about gas gumming up. Gas in California is especially bad now .... I guess that's progress?

 

[CobyRupert]

Depending who you ask, diesels can get touchy starting below 40 degrees, or 32, or maybe no problems at all. Diesel fuel can start to wax/gel below 32F, maybe lower, maybe higher, depending on your supplier/ blend. With cold temps and diesels you're in the world of fuel treatment (or blending), glow plugs, block heaters, etc..

 

[fatjay]

I don't believe diesel has longevity over gas when properly maintained. I have a 1951 ferguson and a 1953 oliver gas which still run like a top. They're easier to repair with their carburated fuel system vs direct injection and pump. They take less oil, and gas can be treated to last well over the winter and longer. Diesel is also considerably more expensive for the fuel and for the motor. Diesel motors are also much dirtier for exhaust, there's numerous countries trying to ban diesel vehicles all together because of the pollution. In the winter with low temps, gas is much easier to start than diesel as well.

That being said, I love my 2 kubota diesels. They're quieter when running and don't take a lot of fuel when doing it. I have mowed 4 acres 4 times on about 2 gallons of diesel with my kubota zero turn, with my craftsman I need to fill up the 2 gallon tank every 4 acres, so 2 gallons per mow, 4 times, 8 gallons. My diesels seem to never bog unless the circumstances are extreme. I can store a lot of diesel safely, where gas i have to worry about vapors.

In the end there's really no clear winner, both have their trade-off's. I prefer diesel, but I wouldn't write gas off completely.

 

[Ford850]

I think the EPA limitations are keeping the small diesels, well, small. That's allowing for some larger gas engines into these lineups. If comparing gas vs diesel of equal HP, diesel wins. These newer, larger, gas engines are passing the diesels in power. They are thirsty though.

 

[Sawyer Rob]

I don't believe diesel has longevity over gas when properly maintained. I have a 1951 ferguson and a 1953 oliver gas which still run like a top. They're easier to repair with their carburated fuel system vs direct injection and pump. They take less oil, and gas can be treated to last well over the winter and longer. Diesel is also considerably more expensive for the fuel and for the motor. Diesel motors are also much dirtier for exhaust, there's numerous countries trying to ban diesel vehicles all together because of the pollution. In the winter with low temps, gas is much easier to start than diesel as well.

You just can NOT make the above blanket statements...

MY diesels start just as easy, in fact in most cases, easier than my gas engines and it does get quite cold here in the winter...

OFF ROAD diesel here cost LESS than gas, but both keep going up and down in price...

There's NO doubt that diesel stores easier, longer than gas, so I'm not sure how you came up with the opposite?

To the OP, I had the exact same choice when I bought my new Grasshopper... I talked to guys that chose the gas and all of them complained about the amount of gas they burned and didn't like how gas stored long term for them...

I chose the diesel and I'm so glad I didn't choose the gas motor... The diesel starts easily and really has excellent torque, plus it's very easy on fuel...

SR

 

[prs]

I have the Kubota gasser. The extra HP and torque was strongly recommended to run my choice of mower, the big 7' contour. It handle it well. Here in WV I am constantly on slopes, but the limitations are for continued severe slope over long periods in same direction. If you are mowing around a sloped field it is unlikely you would be leaning the same way that severely for so long. I have certainly suffered no ill effects yet. I do not have to choke the engine once it is up to operating temp. I use fuel preservative in gas and diesel and have no problems there either. If your other equipment is gas, that should answer your question; if diesel, again your question is answered unless you worry about the power difference. The diesel members here seem quite content.

prs

 

[zmountaineer]

Kubota gas FTW! Ventracs have to be run WOT...push that lever all the way forward and you're good to go......basically useless under 3000 rpms. Put on some hearing protection and get on to tractoring.

But seriously, I've got the gasser and it's handled everything that I've thrown at it. My hills are steep and brush is thick. I've only lacked power going up a 45 degree hill mowing 3ft high grass. Just had to let off the "go" lever a little and proceeded to crawl up the slope uninhibited. I've never run the diesel but I know someone with one and he says it "seems" underpowered....I have never felt this way with mine. As "rare" as these tractors are, there are 6 within a square mile of my house. I drive by 2 working daily.....golf course and housing development. I expect my gasser to last many thousands of hours.

 

[plowhog]

I believe the 25hp diesel burns 1.1 gph and the 32hp gas burns 1.5 gph.

It's hard for me to evaluate the benefit of using/needing the extra HP and torque compared to the increased difficulty of storing gas (instead of diesel) and a higher fuel burn. The higher fuel burn to make more power is understood-- there is no free lunch of course!

I probably have an equal mix of slopes (that could benefit from horsepower) and flat areas under the canopy of trees, etc, which would not need the extra power.

 

[prs]

Dodge dealers have said for years; "it is always good to have MoPar".

Mountaineer, my 4500Z is at red line full throttle, I usually run it so that I am at 3000 to 3200 while under load.

prs

 

[zmountaineer]

Dodge dealers have said for years; "it is always good to have MoPar".

Mountaineer, my 4500Z is at red line full throttle, I usually run it so that I am at 3000 to 3200 while under load.

prs

Yeah. It sits just below redline sitting still but goes down once you start moving/engage pto. I saw someone (dealer) post a picture of the transaxle pumps in one that didn't run full throttle vs one that did and needless to say, I'm running full throttle.

I want a Ventrac one day Public Group | Facebook

 

[DoubleDeere]

Which deck you planning on running with it? I run the 60" with my 440 Steiner 25HP diesel and 68" Ventrac tough cut. The larger decks are gonna take more power to push them. How fast do you want to mow? Small tires and short wheel base limit how fast you can go on rougher terrain. Dual wheels might also rob more power, not sure I have singles with extenders on them. I like to mow fast. What was it Lee Iacocca use to say? Move over or get your butt run over. Something like that anyway. My set up does pretty good at keeping a fast pace. So when selecting the engine also consider how fast you can actually go ( terrain limited ), how fast do you want to go and deck size.

 

[plowhog]

I'm told the contour mower requires the most power. Which makes sense. I will probably only use the 68" tough cut. With dual wheels and a small lawn, using the finish cut mower might not make sense. My needs are all met with the tough cut.

I think the idea of "move over or get your butt run over" is great for street machines. That's why I have a 1969 Plymouth Roadrunner 426 hemi in my garage. :laughing: But I go at moderate speed when mowing.

My slopes can probably be mowed up, turn at the top, down, turn at the bottom, and go back up. So I presume I am returning to "flat land" each time which would reset the 10 minute clock on the max time to run while on a slope?

 

[MossRoad]

I'm told the contour mower requires the most power. Which makes sense. I will probably only use the 68" tough cut. With dual wheels and a small lawn, using the finish cut mower might not make sense. My needs are all met with the tough cut.

I think the idea of "move over or get your butt run over" is great for street machines. That's why I have a 1969 Plymouth Roadrunner 426 hemi in my garage. :laughing: But I go at moderate speed when mowing.

My slopes can probably be mowed up, turn at the top, down, turn at the bottom, and go back up. So I presume I am returning to "flat land" each time which would reset the 10 minute clock on the max time to run while on a slope?

So how much lawn are you thinking about mowing with this? If it's only a couple/three acres, your fuel consumption costs between gas VS diesel over the course of a year are gonna be negligible.

You had some questions about the Power Trac in the other forum, correct? When I was researching the PT, I was going back and forth between the PT422 and PT425. How much difference could 3hp make? I wanted to run the 60" mower, not the 48" mower. The factory said the 3 extra hp made a huge difference and recommended I not buy the PT422 if I wanted to run the 60" mower. I've never regretted the extra HP.

In your case, your gas VS diesel, the gas has about 25% more torque AND about 25% more horse power. If you want to spin a large mower deck you need horsepower, and if you want to keep it spinning when you hit tall grass, you need torque. You're getting more HP and more torque with the gas engine option.

 

[DoubleDeere]

I have found in my usage that the tough cut takes less power to run than the finish mower in tall grass. There is no baffling under the tough cut so it does very little if any mulching of the the grass or brush being cut. So you will not have as nice of a finish with that as you would the finish mowers. The move over or get your butt run over is what I tell my wife if she is helping me mow on our JD2025R and I am on our 790. It is a gear shift and I won't stop to drop a gear unless I have to, so she is told stay out of my way . I pretty much am at a moderate speed with the Steiner as well because of our terrain. Some of the commercial guys (understandably) like to run them all out.

 

[buickanddeere]

As previously stated this is a modern gasser operating on unleaded fuel and is probably fuel injected . The gasser will start in cold weather easier . The gasser is easier to start after it is ran out of fuel. Today’s Tier IV emissions diesel is not the low cost and reliable diesel of 20+ years ago.