On modern Kubota tractors, you might notice a small blue cap next to the diesel filler port. This is for adding diesel exhaust fluid (DEF). Many people wonder: Does my tractor need this? And how do I use it correctly? Let’s answer these questions.
What is DEF?
Diesel exhaust fluid (DEF) plays a role in selective catalytic reduction (SCR) systems to remove nitrogen oxides (NOx) from engine exhaust. DEF is a solution of 32.5% high-purity urea and 67.5% deionized water mixed precisely. This specific ratio is very important because it can provide the lowest possible freezing point. In an SCR system, DEF is sprayed into a high-temperature exhaust gas stream. Then, a chemical reaction occurs to turn harmful nitrogen oxides (NOx) into two harmless substances: nitrogen and water vapor. Simply, it makes the air that comes out of the engine cleaner and greener. The DEF tank is identified by its blue cap. There are some characteristics:
- Non-toxic
- Non-flammable
- Non-hazardous
- Classified as safe for transport
Do Kubota Tractors Use DEF?
The answer is simple: it depends on how much horsepower your tractor has. In general, Kubota tractors above 75 hp are equipped with SCR systems, which necessitate the use of diesel exhaust fluid (DEF). This was not a haphazard design by Kubota himself, but rather to comply with the requirements of the US Environmental Protection Agency’s (EPA) Tier 4 Final emission standards.
These standards are strict limits on emissions from diesel engines. For high-power engines, the SCR system is currently the most effective solution. It drastically reduces exhaust pollution without sacrificing power, making tractors both dynamic and more environmentally friendly.
Kubota Tractor Models That Require DEF
So, which Kubota tractors use DEF? SCR systems are primarily installed on medium to large-sized utility tractors and agricultural tractors in Kubota. If you own or plan to purchase the following series of tractors, they almost certainly require the use of DEF:
M Series: This is the mainstay of Kubota’s product line and the series that most widely uses SCR/DEF technology.
- M5 Series: Includes standard and narrow track types and is a popular choice for farms and multi-purpose operations.
- M6 Series: Provides higher horsepower and stronger operating capabilities, and the SCR system is standard on all series.
- M7 Series/M7 Gen-2: This is Kubota’s flagship large agricultural tractor with state-of-the-art technology. Its powerful engine must rely on the SCR/DEF system to meet emission standards.
- M8-Series: As Kubota’s current most powerful tractor series, the DEF is an integral part of its high-performance engines.
MGX-Series: Before the launch of the M8 series, the MGX series was Kubota’s main high-horsepower model, and the entire series was also equipped with the SCR system.
Not All New Kubota Tractors Use DEF
Many people think that the use of DEF (diesel exhaust treatment fluid) for tractors depends on the year of production, but this is not the case. The real determining factor is the amount of horsepower the engine has. Many of Kubota’s new tractors, especially the smaller compact and ultra-compact models—— do not require the use of DEF because of the power of less than 75 hp, which does not require an SCR system. The BX, LX, and L02 series are very typical examples. This type of tractor is lighter and simpler to maintain, making it ideal for gardening, site maintenance, or use on small farms.
Quick Reference Table: Does Your Kubota Require DEF?
To keep you informed, here’s a quick reference. The safest way is to check for the blue cap near the fuel tank.
| Series | Typical HP Range | Requires DEF? |
|---|---|---|
| BX Series | 16 – 25 HP | No |
| B Series | 20 – 33 HP | No |
| LX Series | 25 – 40 HP | No |
| L Series | 25 – 48 HP | No |
| MX Series | 55 – 63 HP | No |
| M5 Series | 92 – 105 HP | Yes |
| M6 Series | 101 – 141 HP | Yes |
| M7 / M8 Series | 128 – 200+ HP | Yes |
Handling and Storing Diesel Exhaust Fluid
It contains high-purity water, so when stored at low temperatures, it may freeze at a temperature of about -11°C (12°F). DEF Thaw Control Mode is an automatic heating mode after the engine is started. It is used to defrost ice in the diesel exhaust treatment fluid (DEF) at low temperatures. Once it returns to the liquid state, the system can work normally. But you should try to store bulk containers above this temperature.
On the other hand, if continuously exposed to temperatures above 30°C (86°F), DEF decomposes into ammonia, reducing its effectiveness. The ideal storage temperature is 5°C (40° F) to 27°C (80° F). Here are some tips for keeping DEF:
- Store it in a sealed, clean container made just for DEF.
- Keep it in a cool, shaded, well-ventilated place.
- Don’t pour it into old fuel, oil, or coolant jugs—any contamination can ruin the system.
- Good DEF should be clear. If it looks cloudy, tinted, or smells like ammonia, don’t use it.
Notice: DEF contains urea. While non-toxic, it can irritate your eyes. If you get it in your eyes, flush them with water for 15 minutes. Do not ingest DEF.
How to Check the DEF Levels on a Tractor
Kubota makes checking your DEF level simple. Depending on your model, you’ll have one of three methods:
- Sight Glass: Many DEF tanks are made of translucent plastic with a level scale on them. You can see the fluid level at a glance.
- Oil dipstick: Some models also come with a special DEF dipstick to check the level as if you were checking the oil.
- Digital Display: Most modern Kubota tractors with a digital dashboard will display the DEF level as a gauge, right alongside your fuel level.
Filling the DEF
The DEF tank is almost always located near the diesel tank, but it is clearly marked with a blue cap. Diesel fuel caps are typically green or black. Never put DEF in the diesel tank, and never put diesel in the DEF tank.
Use Only High-Quality DEF
The SCR system is highly sensitive to impurities. To use with confidence, look for DEF that is certified by the American Petroleum Institute (API) or carries the AdBlue® trademark.
How Often Will You Need to Fill up DEF?
DEF consumption is directly related to fuel consumption. For off-road machinery like a Kubota tractor, the DEF consumption rate is typically around 2-3% of the diesel fuel you use. A common interval is refilling the DEF tank once every two or three times you fill up with diesel. However, you don’t need to guess. The best approach is simply to top off the DEF tank whenever you refuel. More importantly, your tractor is designed to give you plenty of warning before you run low.
Operator Interface & Warning Indication
Your Kubota tractor is equipped with an advanced, multi-stage warning system to prevent unexpected depletion of diesel exhaust fluid (DEF). This “operator inducement” system, required by law, is designed to get your attention by gradually reducing engine performance. Here are the warnings you’ll see:
- When the diesel exhaust fluid (DEF) level is too low (for example, 15% remaining), a yellow warning light will illuminate on the instrument panel. You may also hear a repetitive beeping sound.
- Power reduction. If you continue operating without replenishing DEF, the yellow warning light will begin flashing, and the engine’s torque and power will decrease by 25-50%.
- When the tank is nearly empty, the warning light will turn flashing red, and the buzzer will sound a loud, continuous tone. The instrument panel will indicate that a full power reduction is imminent.
- If the DEF tank is empty and not refilled promptly, the red “Stop” light will illuminate. The tractor will not be able to drive or operate normally. Once the DEF tank is refilled, the warning light will automatically disappear and the engine will immediately resume normal power.
Engine Stop – Cool Down And DEF Purge
The DEF injection stops immediately after you turn off the engine. But the system will continue to let the pump run, cool the nozzles down, and pump all the DEFs in the line back into the tank, preventing the liquid from freezing inside the tube. So, do not disconnect the battery after stopping work, and wait a dozen or so minutes for complete cooling and DEF removal.
Final Thoughts
Do Kubota tractors use DEF? A large tractor with more than 75 hp will almost always need to use DEF. This is a necessity for compliance with emission regulations and a necessity for environmental friendliness. If your Kubota tractors fall into this category, it’s important to maintain the DEF system regularly. Parts like DEF Filter, injectors, and NOx sensors can affect the proper operation. At FridayParts, you can find a wide range of high-quality Kubota tractor parts and DEF parts, compatible with many models. Help you keep your tractor running smoothly and emissions up to standard.
