Can I Use Regular Diesel In My Kubota Tractor?

Diesel is an entirely new ballgame for those who have spent their lives filling up their lawn equipment and vehicles. It can be a bit confusing, especially if you just purchased a diesel-run Kubota tractor for the first time. There are, of course, the Kubota recommendations, and then there is diesel that may or may not be considered safe. 

You can use regular diesel in your Kubota tractor. The dye is the only difference between regular and red diesel fuel. Red dye is used in off-road diesel so that easily differentiated. That’s important because red diesel is tax-free and used for construction and farming applications.

There is also a “green” diesel, but unlike the red diesel, it’s not called “green” diesel because it is dyed. It’s called “green” diesel because it contains more biomass and is supposed to be more environmentally friendly. You are not supposed to use red diesel for standard vehicles on the highway. 

Red Diesel, Green Diesel, and Regular Diesel

Diesel is diesel, and you could technically use it all interchangeably. You aren’t supposed to place red diesel in your car or truck because it is tax-free, making it illegal to put it in your vehicle for driving on the highway. 

Your Kubota tractor will run just fine on the green, red, or regular diesel. However, if you choose the other two, you will miss out on the tax-free benefits of filling it up with red diesel. This is because the red and green diesel is manufactured with ultra-low sulfur content.

Regular diesel (gas with no ethanol), like regular unleaded gasoline, is getting harder and harder to find. So most of the time, your choices at the pump will be red and green, which are the same, with the red dye being the only significant difference between the two. 

Kubota’s Recommendations on Diesel Fuel Use

According to Kubota, there is no reason that you can’t use diesel fuel with 500ppm sulfur. The company extensively tests all the engines with

500ppm diesel and without any adverse effects. 

Kubota also recommends that you only use diesel fuel that has been refined to a point where it meets the standards of the day for on-road and off-road use. However, Kubota also makes it very clear that they are not responsible for engine or component damage caused by ULSD Diesel (Ultra-Low Sulfur Diesel). 

While that last disclaimer might make you a bit concerned, Kubota has claimed that all of their engines have been extensively tested with the stuff, so you will have to make your own judgment call where that is concerned.

Also, according to Kubota, a few applicable biodiesel fuels are safe to use in Kubota engines. 

  • Blended diesel fuels
  • Mineral oil diesel fuels
  • B100 blended biodiesel fuel

All biodiesel fuels are annotated with a B followed by a number. For example, one biodiesel fuel may have an associated B6 next to it, while another may have an associated B20. If you see the “B” followed by a number, you know that, at the very least, there is a blend of biodiesel fuel in the product. 

The number behind the “B” indicates the percentage of biodiesel blended with regular diesel fuel. According to Kubota, blended diesel with B6 through B20 biodiesel blends are perfectly fine for use in Kubota engines. 

Mineral oil diesel is also OK with Kubota engines. However, it has to conform with the ASTM D975-09b standard. In addition, the B100 biodiesel fuel must conform to ASTM D6751-09a standards, and the B20 biodiesel must conform to ASTM D7496-09a standards. 

ASTM stands for American Society for Testing and Materials. You will find this acronym on nearly everything requiring testing to a certain standard. 

That includes diesel fuel, football helmets, safety vests, construction safety gear, etc. So if it has to do with safety, you can expect to see an ASTM label. 

Lastly, the biodiesel blends, from Kubota’s recommendations on diesel fuel in their engines, must come from a BQ-9000 accredited marketer or producer. 

Additional Kubota Recommendations for the use of diesel

Anything below B5 doesn’t require you to do anything extra or out of the ordinary, at least insofar as Kubota is concerned. For biodiesel blends that exceed B5, however, Kubota recommends changing your oil, oil filter, and fuel filter before you run your Kubota tractor. 

While diesel, whether it is a blend, mineral, dye, or regular old diesel, all burns the same. However, Kubota recommends that when you increase the amount of biodiesel blend to above 5%, you should start from scratch on everything. 

Filters will help clear out anything that could be large or damaging to the engine, so it’s good to start with fresh, clean filters when you change your fuel source.

Caveats in Your Product Warranty

Although Kubota claims to have extensively tested their engines with various biodiesel blends, that simply means that they have tested their newest engines, not the older ones. 

Kubota makes it clear that its engines are certified based on “today’s” regulations. 

Does that mean your older Kubota engines won’t run some of these higher biodiesel blends at the end of the day? No, they will definitely run them; however, some things are worth considering. 

We all know that the increase in ethanol percentage in unleaded gasoline products has created more rapid wear and tear problems on older vehicles. However, it didn’t break them; it simply shortened their overall lifespan.

It’s a similar situation here, except the future possibilities are a little more unclear. There are also a few more “mights” and “maybes” that Kubota throws out there. 

  • During cold weather, biodiesel may clog your fuel filter or restrict it in some way
  • Microorganisms tend to grow in biodiesel, which is detrimental to the fuel itself
  • The more biodiesel that is in the blend, the more it absorbs water, which is detrimental to both the fuel and the engine
  • Kubota warns not to modify the fuel control system, or you will violate your warranty and emission levels
  • Fuel filter performance may go downhill
  • The Kubota warranty covers none of these potential eventualities

None of these things sounds very appetizing. However, there have been no known systemic issues with Kubota engines, despite the rise in biofuel blends from a percentage standpoint. 

Kubota also advises you to ensure that you have a full fuel tank before short-term storage and that you tightly seal the fuel cap to reduce water absorption. They also recommend completely draining the fuel tank before long-term storage if you have a tank full of biodiesel above B5 percentage levels.

Kubota also recommends replacing the biodiesel with light mineral oil diesel fuel if you place it in long-term storage. 


While Kubota and other experts view biodiesel, red diesel, green diesel, and regular diesel as perfectly fine for use with their engines. There are still a lot of unknowns out there. 

In other words, exercise caution and follow all of Kubota’s recommendations. If you’re unsure of what type of fuel to use, check the owner’s manual or contact the manufacturer directly. 

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