How to Fix Common Kubota KX040-4 Excavator Problems?


Are you hesitating to buy Kubota mini excavator before knowing its problems? What are the Kubota KX040-4 problems that its users have faced?

Frequent regen cycle occurring, weak power output, abnormal exhaust gas color, starting issues, and overheating are some of the most common problems of the KX040-4 mini excavator.

The best part of this article is that it not only shows the reliability and durability of the machine but also gives you solutions to those problems. Without further ado, let’s get started.

Problems and Solutions at a Glance:

Problems with Kubota KX040-4Solutions
More frequent regen cycles than usualRun at high RPM, keep the exhaust hot, and check the EGR valves, turbochargers, and injectors.
Getting low output power while runningClean the water separator and fuel tank, change O-ring, and tighten the nipples on the fuel separator.
Not starting the engine or sluggish startCheck battery voltage, lever status, loose nuts or bolts, or pour hot water on the radiator.
Seeing abnormal colors of the exhaust gasBuy good-quality fuel, and don’t pour too much engine oil.
Engine showing overheating warningCheck the water pump seal, thermostat, and any clogged or corroded parts, and take action accordingly.

Common Kubota KX040-4 Problems and the Solutions

After going through lots of comments in different forums, I have found the following 5 problems worth mentioning. 

1. Keeps Going into Regen Cycles

Keeps Going into Regen Cycles

One very common complaint of KX040-4 users is that their excavator engine keeps getting into regen cycles more frequently than usual.

It is a bit troublesome because you have to go through a certain regen process to make it work again.

The problem can arise due to excessive idling or light-duty cycles. Also, if EGR valves, turbochargers, and injectors don’t work properly, it can cause this.

The purpose of the regen process is to remove particulate matter or unburnt fuel from the system.

The Fix

  • The first thing to do is to keep the exhaust hot by working the excavator hard. Revving the engine at high RPM ought to do it.
  • After that, check the EGR valves, turbochargers, and injectors and make sure that they are working perfectly.
  • Lastly, you should contact your dealer to look into this particular problem if none of the solutions work.

Also, don’t hesitate to put it under warranty in case the issue occurs within 5 years of purchase.

For more information on the matter, you can read this article explaining the regeneration process.

And, the FAQ section at the end of this article contains the process of doing regeneration by yourself. Don’t forget to check it out.

2.  Not Running at Full Power

Not Running at Full Power

I saw some customers complaining about their Kubota mini excavator not running at full power.

The reason for this problem is almost endless. Among many, lack of pressure, excessive friction, weak charge pump, low fuel, and worn-out parts are common.

But this particular case I’m talking about has something else. The user checked the fuel filter, air filter, and injectors.

And, he replaced them with new parts. Still, the problem didn’t solve. After some trial and error, he finally found the issue which is with the air bleeder valve.

It is located at the top of the fuel filter block.

After putting a clear hose onto the air bleeder valve and ejecting the air completely, the user noticed air bubbles in the fuel stream.

The Fix

  • To solve this problem, clean the water separator to the point of showing no air bubbles in the visible area.
  • After that, put in a new O-ring.
  • Then, remove and clean the fuel tank removing the fuel level sensor.

Pro Tip: You should clean the tank so thoroughly that you could drink out of it. Absolutely no sediments should be left.

  • Now, use compressed air to blow out the line between the water separator and fuel tank.
  • Finally, check the nipples on the fuel separator. If loose, use glue or crimping so that air can’t get in.

Slow speed can be a complex problem that needs proper diagnosis and treatment.

Those who don’t have the proper tools or expertise should not wait or try different things, and take the machine to the dealer as soon as possible.

3.  Difficulties Starting the Engine

Difficulties Starting the Engine

According to some other users, the Kubota KX040-4 shows issues while starting the engine.

You may notice that the engine is cranking hard but not getting started.

One of the most common reasons is a dead battery which can’t provide enough cranking amp to start the engine.

Cold weather can also be responsible sometimes.

Some levers that are supposed to be locked can be in an unlocked position making the engine signal not to start.

When the fuel is too sticky or there is air or water in the fuel system, you may experience this issue.

Even if it starts, it is possible that the excavator runs sluggishly in winter because of too high oil viscosity.

The Fix

The solutions are simple. Let me tell them one by one according to the cause.

  • First of all, check the battery voltage to make sure that it is working properly.
  • Secondly, buy a new battery if necessary. And, ensure a high CCA rating which is an important factor for cold region operation.
  • Thirdly, check the status of the levers, and switch them back to the lock position.
  • Fourthly, remove water or air from the fuel tank by cleaning, check the nuts and bolts for looseness, and purge the whole fuel system if needed.
  • Lastly, pouring hot or warm water over the radiator in the winter season can solve the oil viscosity problem.

4.  Abnormal Color of the Exhaust Gas

Abnormal Color of the Exhaust Gas

Have you ever noticed that the color of the exhaust gas is not normal?

It is a fairly common problem for a silly reason.

When you use poor quality oil or too much engine oil, it can happen.

The Fix

The solution is simple here.

  • Buy good quality oil which may be costlier but keeps the maintenance cost low.
  • If you have poured too much engine oil, you can drain some and make it to the prescribed level. Don’t wait for it to burn out.

5. Overheating Warning

Overheating Warning

In case of seeing the water temperature level in the red zone, you should take immediate action to mitigate the issue.

The defective seal of the water and worn-out V-belt is two of the most common reasons for this issue. Sometimes, the V-belt can be torn completely.

Also, when the thermostat is defective or the coolant level is too low, you can experience it.

Among other complaints, I have also noticed a clogged radiator grill, contamination in coolant, defective radiator cap, and corrosion in coolant pipes.

Lots of users don’t want to agree but continuous operation under full load can also cause an overheating problem.

The Fix

  • Firstly, check the seal of the water pump, and replace it in case it is defective. Also, inspect the condition of the V-belt and take necessary actions.
  • Secondly, replace the thermostat after making sure that it has become faulty. Here’s a technique you can follow to check its condition.
  • Thirdly, pour more coolant and fill to the recommended level. Your user manual has the information on the prescribed level.
  • Fourthly, clean any clogged parts and replace any corroded or defective parts for better performance.
  • Finally, try to run the machine under reduced load. And, don’t use it continuously for long hours. Having a break every hour or two is good for both the operator and the machine.

What Majority of the Users Feel?

Like any other excavator on the market, the KX040 also has some. But that doesn’t mean that users don’t like it.

People trust Kubota because of its low repair bills, low running costs, and reliable performance over the years.

And, that sentiment does not change for the Kubota KX040-4 model.

I have seen users being very pleased about its performance when it comes to rock wall construction.

It is a well-balanced machine making it suitable for performing heavy-duty tasks.

Frequently Asked Questions (FAQs)

Are Kubota mini excavators any good?

Yes, they are good but not problem-free.

How much does a new Kubota KX040 4 cost?

About $70,000; but check the latest price as it can change anytime.

How many hours do Kubota excavators last?

Ensuring well maintenance, you should get almost 10,000 service hours from it.

How deep will a Kubota KX040 dig?

About 11.3 ft.

How do you regen a Kubota kx040?

This video explains the process briefly.


If you have used any Kubota machines before, you will know how reliably they perform in real life.

I, along with many experts, like this mini excavator for its perfection in certain applications.

Except for one, other problems mentioned above are common among other brands. So, it should not affect your buying decision.

A know that lots of people hesitate before making such investments seeing so many problems. But the solutions are there too.

So, it will be possible to tackle unwanted situations when it comes to Kubota KX040-4 problems.

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