2017 Kubota RTV-X900 a lot of white smoke out the exhaust and loud knocking


2017 Kubota RTV-X900
1100 hrs

I’m having this issue the engine will fire right up. It’s billowing white smoke out the exhaust pipe and knocking very loud. Also seems to be running rough.

Wondered if anyone else has had this issue and what should I check first with these symptoms?

Thank you
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white smoke = water = either cracked head, head gasket or cracked block. Kubota engines are very robust except they don't do overheating very well. Once your engine overheats you can expect to replace the head. Fortunately aftermarket heads are inexpensive and plentiful. The Kubota heads are expensive. I am a huge advocate of buying kubota parts but the aftermarket head on I put on my 900 worked very well.


I had a partially blocked injector in my backhoes engine (Perkins 1004-4T). While driving on my driveway up an incline I noticed more black exhaust soot than normal. I normally have BT stereo headphones on when I'm out plowing. So I didn't hear any engine noises then.

A short time later I was driving with the headphones off and heard the racket. It literally sounded like a rod was going to come out of the side of the engine block when I accelerated. So before I really dug into the engine I thought I'd try cleaning the fuel system with some seafoam. I followed the directions on the can which involved adding SF to the tank and also dumping the fuel filter bowl, changing the FF, and refilling the FF housing with SF. Then running it hard for some time, then letting it heat soak, then running it hard again.

It cleared up the issues I was having thankfully.

Now I know the OP said white smoke. Sounds like a cracked head to me. But it wouldn't take much $$ to rule out a dirty injector first.

Good luck OP.


I was thinking water too but…
It’s not pushing water out of the radiator. It’s not boiling in the overflow and the temps seem to be stable.

It does smell more like fuel than a sweet coolant smell we use 50/50 here in Hawaii.

Black soot in the tailpipe

This is a machine we picked up in an auction so I don’t know much on the history.

If I crack a nozzle line loose and the smoke and knocking go away would that rule out a water issue?


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Could be that your glow plugs are heating up enough and you have unburned fuel. It will knock in this case. Does the white smoke and knocking disappear after running a while?


Are you having to add to the radiator? Seems to me that if the head/block is cracked or the gasket is blown, it would be "using" coolant and you would have to top off the coolant regularly. JMHO


So far I have not added any water yet and the radiator seems to still be full.

The first time I started it white smoke and knocking then the smoke went away but the knocking was still there.

Second time I started the machine white smoke and knocking stayed all the way till it warmed up and I shut it down.


So I narrowed the white smoke down to Cyl3 cracked the fuel line and smoke went away. Low compression not firing. Pulled the cylinder head and found slight coolant on the inside of valve cover and inside the intake manifold.

Pistons are proud of the deck on 1 and 2
Piston on 3 never gets flush or proud and sits 1/4” below the deck. So this is where the knocking sound is either a rod bearing or bent rod or both haha. The crank will spin smooth than lock up with big resistance than spin smooth again. It gets hard to spin when piston 3 is reaching BDC and on the way off BDC.
I’m taking the head to machine shop for inspection for cracks and if it will be usable.

Don’t see any obvious signs of a blown head gasket or cracks on head but I’ll leave that up to the machine shop.


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We’ll it could have been much worse.
Rod is bent and piston was hitting the crankshaft counter weights.

Cylinder ok just needs surface hone
Crank shaft journals ok

Still waiting to hear back from machine shop and I really need to inspect this block well to make sure there’s no cracks in it


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