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