Mule 610 - Fuel In Oil?????


We have a 2007 Mule 610 purchased new in the fall of 2007 that currently has about 173 hours on it.

We had it serviced at the dealers at about 50 hours in order to have a service record for the warranty.

At about 110 hours it started running rough when going up a steep hill and began to smoke profusely.

I checked and the oil level was VERY HIGH and upon draining the crankcase it seemed that there was fuel was in the oil.

I changed the oil and filter and kept a watch on the level for the next 20 -30 hours and then got lax.

Today I changed the oil and filter again and the level was once again high with what appears to be fuel in it.

I have contacted Kawasaki and they claim that they have NEVER had anyone else with this problem.

One local dealer's Mule service 'expert' tried to convince me that it was coolant, possibly from a leaking head gasket. I questioned him how an air cooled engine could leak coolant into the oil and he was befuddled and then insisted that I must be driving it through the river to get water in it.

It has never been driven in water and it is definitely not water as it mixes with the oil and DOES NOT separate as water does if the drained mixture is left to stand.

The Mule is almost impossible to start without using the enrichment device and as we generally only ride it from the house to the horse barn (a distance of about 1500 feet) it never gets really warmed up. I suspect that the fuel enrichment device is dumping too much gas into the intake and it is not being run long enough to get burned up and is getting into the crankcase.

A neighbor has a Mule 600 that I service and the oil in it is just dirty, not at all like in our mule and the level is not high. BUT he runs his much longer than we do when he uses it.

Has anyone had a similar experience.

Any help would be greatly appreciated.



If it is carbureted and you are not shutting the gas off when it is parked sometimes your float will stick and allow fuel to seep through the carb, head and down into the crankcase. I had this problem with an atv once and as long as I shut the gas off when it wasn't running the problem stopped.

true law, years ago when I had my mojave 250 I was going to the safety class kawasaki paid me for.Well duhh me forgot to turn gas of bouncing on trailer for 50 miles flooded out bike.It was soo embarrasing I ended up walking out so not to hold up the others.Fixed the problem an never got back or got my money learned by just ripping it up an understanding the logistics of the machines if that makes sense too you.

LawMonkey & RebelYell;

Thanks for the input.

Our (2007) Mule 610 is indeed carbureted. However, unlike most motorcycles and (sit astride) ATVs the gas tank is not above the engine but is in fact lower than the carburetor. As a result of this it requires a fuel pump to deliver fuel to the carburetor. For this reason there is no fuel shut off in the system.

Also, as the carburetor mounts to the side of the head (in a pretty much plumb and square position) with the float bowel being lower than the intake tract it would be difficult (though certainly not impossible) when the Mule is parked on a level surface for the fuel to run up into the intake tract.

If the float needle was sticking open and conditions were just right it is remotely conceivable that the contents of the float bowel could possibly flow into the intake tract. But the engine must be turning over to generate vacuum to make the fuel pump draw fuel from the tank into the fuel lines to fill the float bowel again. If that anomalous condition persisted over time it is imaginable that enough fuel would be leaked into the intake tract to raise the oil level as has been experienced.

I can’t remember if I took off the carburetor and checked the float needle when this first happened a few years ago or not. If it had been a motorcycle or a normal ATV that is one of the first things I would have checked. But for the above mentioned reasons I have pretty much discounted that possibility, though I may have erred in doing so. Perhaps when it warms up some (it’s in the low 20s now) I’ll pull off the carburetor and check out the needle and seat.

Thanks again for the input, all suggestions are most welcomed.


Now that I know it has a fuel pump your problem most certainly is a bad diaphram in your fuel pump. That is the only other way fuel could get to the crank case.

That would also explain the bad running.


Thanks for the great insight on the possible fuel pump diaphragm issue.:moon:

The fuel pump is a sealed and non repairable but a new one is only about $25. I can certainly imagine that a very minute pin hole in the diaphragm might cause this problem. As the vacuum from the crankcase flexed the diaphragm it could cause a diminutive amount of fuel to be drawn into that vacuum line and therefore get back into the crankcase.

As I mentioned in the first post it only ran rough the one time when I was going up a very step hill and the oil level was too high. After changing the oil (and filter) it went up the same hill without any problem. So it was the excessive level of fluid in the crankcase that caused the rough running and smoking because when at the steep angle it got into the combustion chamber. It starts and runs great.

But it possible that a hole would be so small, or the diaphragm could have been improperly installed and is not seated correctly, that a minute amount of fuel is getting into the vacuum line. It takes about 50+ hours to see a noticeable increase in oil level.

Again, thanks for the insight. I will definitely check it out.


Well after 10 hours since the last oil change the Mule started running rough again so I checked the oil level and it was AGAIN high.

At one of the forum member's suggestion I checked the fuel pump. I discovered that it was NOT a vacuum pump but worked on a pressure pulse. This meant that it would have been impossible for a malfunctioning pump to ‘suck’ anything back into the crankcase. As it was questionable on one of the service manual tests I replaced the fuel pump anyway.

I had taken off the carb to check the float level and this is what the intake track looked like.


I again drained the oil and this is what the oil looked like after only 10 hours since the last change.


I again contacted Kawasaki and this time I got a service tech that (sort of) admitted that there was an issue with this model.

After describing what was happening the individual asked what were the conditions in which the unit was used in. I told him that my wife drove it about ¼ mile down to the horse barn and back to pet her horses twice a day. He said that she was not getting it warm enough to burn off the condensation and that it was going into the crankcase and building up.

Because of the way the emissions are handled in this engine excess 'vapors' are pumped back into the intake tract to be burned.

Because the unburned condensation was raising the oil level this excess 'fluid' was being put into the intake tract and could not be burned, causing the engine to run rough ONLY when the level got very high.

No doubt the lubrication quality of the oil was also greatly diminished.

It is a common problem he said, especially in the winter weather when people drive their mules down to the mailbox and back.

So, according to Kawasaki (even though there is not really an issue with the Mule only with the way Luann uses it) she can:

1.) Drive it every time she uses it far longer than she wants or needs to, (unnecessarily using fuel, tires, etc.)


2.) Get rid of it and get a machine more suitable to her use.

Thanks to those who offered comments.

As the condensation was being 'mixed' so thoroughly with the oil by the emissions system it never displayed the visual separation that oil and water normally have. That is what led me to believe that it was fuel.

At this point I’m not sure what she will do. If it was just me I would sell it in a heartbeat. To go through the expense and time of extra usage is not very practical. And to drain and change the oil every 10 hours is even less so.


I have the same problem, and am getting the same responces from my dealer. Did you ever figure out the promlem with fuel in your oil?

Thanks Tim


The cause of the problem is pretty much detailed in the previous 02-13-2010 post.

As I noted a Kawasaki HQ rep admitted that the cause (in our case) was from not running the machine long enough to 'properly' warm it up and completely evaporate the condensation.

His exact words were pretty much, "Yea, we get this complaint from people who live in cold climates who only drive them to the mailbox to get the mail."

He would not acknowledge that it was a design flaw but did admit that short trips in cold weather were the cause.

In our case it was not fuel but water in the oil, and it was not caused by any malfunctioning part.

Whether Kawasaki will admit it or not in my opinion it is a poor design that requires an engine to be run till it is hot to avoid any type of issue.

We never experience this issue in warm or hot weather but only when it is cold so I am confident that the Kawasaki rep's assessment is correct.

It's just something we deal with in cold weather. If it's not unbearably cold (although we put a windshield on for winter) I will drive real slow so as to make the trip longer and give the engine more time to warm up to reduce or alleviate this problem. With the cost of fuel I certainly can't justify going for a longer ride just to warm up the engine.

So, if you live in a cold climate and only drive your mule a short distance this is probably the issue.


James and all, thank you for the discussion. I also have a 2007 610 mule, with the same issues, I went through much of what you did James. New fuel pump and so on. Didn't help. I find that if I drive it slowly it will crap out, not die but close to it, I keep it running by choking it. Going up a steep hill produces the oil burning smoke.

Yes we live in a cold climate zone teens and twenties in the winter.

I won't buy another one.


Had the exact same issue on a Suzuki DR 350 i had. It ended up being a bad diaphram in the fuel petcock allowing gas to continuously drain into the carb even when not running

just some info. I have a 3010 and mine started running like crap and smoking. I thought it was a bad deal. It only had about 100 hours on it and was getting oil in the air box at the carb. To solve the problem it was a bad air filter that was making the carb suck air from the crank case through the vent hose that is connected to the air box. therefor pulling oil in with the air. just somthing else to watch out for.

We had that happen to our polaris ranger. It got so much condensation in the oil bag that during the winter it froze and seized the motor up. After Polaris has tried multiple attempts to prevent it and we ended up getting a whole new crate motor. We now have a block heater for during the winter and change the oil more often. I used to work at a Honda/Kawi/Yamaha/Canam/suzuki dealer and we always had that problem from running them for about 5 minutes from the front lot to the garage.

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