The most common Kubota RTV 400 problems are a steering shaft that could break on 2012–2015 models (recalled), rising or milky engine oil, backfiring and bogging, fouled spark plugs, low top speed, and dirty air intakes. Many running problems come from short trips and a dirty intake, so they can often be fixed without major repairs.
The RTV 400 (often called the RTV400ci) is Kubota’s compact gas utility vehicle. Unlike the liquid-cooled RTV 500, it uses an air-cooled single-cylinder gasoline engine with fuel injection (a Subaru-built engine on a 2012 model, per its owner) and a CVT. It’s rated for about 25 mph.
Kubota RTV 400 Problems at a Glance
| Problem | Common symptom | Most likely cause | First fix to try | Part you may need |
|---|---|---|---|---|
| Steering shaft (recall) | Loose or failing steering | Steering shaft could break (2012–2015) | Confirm recall repair with a dealer | Recall repair |
| Rising or milky oil | Oil level goes up, oil looks milky | Water or fuel getting into crankcase | Change oil; find the source | Oil and filter |
| Backfiring and bogging | Pops and bogs when throttle is reapplied | Dirty intake, lean running, fuel issues | Clean airbox, fresh fuel, check for leaks | Air filter, spark plug |
| Fouled spark plugs | Black, sooty plugs | Short trips, rich running | Longer run times, new plug | Spark plug |
| Low top speed | 15–16 mph instead of ~25 | Running problems, dirty intake, belt | Fix running issues, check belt | Drive belt |
| Dusty intake | Dust in airbox and hoses | Dusty work, old filter | Replace filter, clean airbox | Air filter |
1. Steering Shaft Recall (2012–2015)
In May 2016, Kubota recalled about 23,400 utility vehicles, including 2012–2015 RTV400 models (serial numbers 10001–22042) and 2010–2015 RTV500 models. The steering shaft could break, causing loss of control. Kubota had nine reports of broken shafts, including a crash into a barbed wire fence. Dealers inspect and repair them for free.
- Check the serial number on the data plate and ask a Kubota dealer if the recall was completed.
- Stop using the machine until it’s inspected if the recall hasn’t been done.
- Watch for any looseness or clunking in the steering.
2. Rising or Milky Engine Oil
One owner of a 2016 RTV 400 with about 60 hours found the oil level rising and the oil looking milky. Because the engine is air-cooled, coolant isn’t the cause. Other owners suggested water entering through the engine vent (deep water or rain while parked outside) or fuel leaking into the crankcase (oil smelling of gas and feeling thin).
- Change the oil and filter before running it again.
- Smell the old oil. A gasoline smell means fuel is getting in; milky oil usually means water.
- Avoid deep water and park under cover.
- Take longer drives so the engine gets fully hot and boils off moisture.
- If it keeps happening, have a dealer inspect it, especially if it’s still under warranty.
Parts you may need: engine oil and filter.
3. Backfiring and Bogging
An owner of a 2012 RTV400ci reported backfiring and bogging when he released and reapplied the throttle, a fouled plug, fuel-smelling oil and a top speed of only 15–16 mph. The airbox and intake hoses were dusty. Replacing the air filters, cleaning the airbox, draining the fuel, changing the oil and plug, and checking the carbon canister valve all helped, though no single fix solved it completely.
- Replace the air filter and clean dust out of the airbox and intake hoses.
- Drain old fuel and refill with fresh gasoline.
- Replace the spark plug.
- Check for intake air leaks, which cause lean backfiring.
- Check the evaporative (carbon canister) valve and sensor connectors.
- If it continues, have a shop run a compression or leak-down test, check fuel pressure and clean the throttle body.
Parts you may need: air filter, spark plug, fuel filter.
4. Fouled Spark Plugs
Short trips stop the engine from reaching full temperature, which leaves fuel unburned and fouls plugs. Give the RTV a longer run regularly, and replace a black, sooty plug.
5. Low Top Speed
If your RTV 400 only reaches 15–16 mph, fix the running problems above first. Then inspect the drive belt for wear and make sure the parking brake isn’t dragging.
Parts you may need: drive belt.
6. Dusty Air Intake
Air-cooled engines working in dust need clean filters. Check the air filter often during dusty work, and keep the cooling fins on the engine clear of grass and dirt.
Useful tools: a battery maintainer helps if the RTV sits, fuel stabilizer keeps fuel fresh, and a digital multimeter helps check sensors and the battery.
Maintenance That Prevents Most RTV 400 Problems
| How often | What to do |
|---|---|
| During dusty work | Check air filter, clean engine cooling fins |
| Monthly | Check oil level and condition, battery, tires |
| Every season | Inspect belt, steering and wiring |
| Per owner’s manual | Oil and filter, spark plug, valve clearance |
| Before storage | Fresh fuel with stabilizer, battery maintainer |
Frequently Asked Questions
Is there a recall on the Kubota RTV 400?
Yes. In 2016, Kubota recalled 2012–2015 RTV400 models (serial numbers 10001–22042) because the steering shaft could break. Dealers inspect and repair them for free.
Is the Kubota RTV 400 air-cooled?
Yes. The RTV 400 uses an air-cooled gasoline engine, while the RTV 500 is liquid-cooled.
Why is my Kubota RTV 400 oil level rising?
Water or fuel is getting into the crankcase. Change the oil, smell it for gasoline, and look for water entry or a fuel leak.
What is the top speed of the Kubota RTV 400?
It’s rated for about 25 mph. Much lower speeds usually point to running problems or a worn belt.
What is the difference between the RTV 400 and RTV 500?
The biggest difference is cooling: the RTV 400 is air-cooled and the RTV 500 is liquid-cooled. See our Kubota RTV 500 problems guide.
Conclusion
If you own a 2012–2015 RTV 400, confirm the steering shaft recall first. For running problems, start with a clean intake, fresh fuel, a new plug and longer run times, and watch the oil for water or fuel.
Related guides: Kubota RTV 500 problems · Kubota RTV models · All UTV problems
