Engine oil contaminated by diesel or Hydraulic fluid?

You may be able to remove your dip stick and rub your thumb and fore finger across the oil. Rub them together a couple of times and then smell your fingers. You should be able to smell diesel on them if there's some in the oil.

This might give you a clue before you drain as North Idaho Wolfman suggested.

You whole problem is hinged on the premise it "leaks a little". A LITTLE in not a measurable description. So a little LITTLE could mean you just need a better seal where the cable comes out!

When the crankcase oil level starts rising the cause is often a failing diaphragm in the mechanical lift pump if your model tractor has one.
Here is a photo of the parts inside a typical lift pump.

The diaphragm is the red part.
When it splits fuel can leak directly into the crankcase. Often owners will say why if the diaphragm has failed will the tractor still run.
Here is a descritpion of operation I provided to another owner.

I cannot speak specifically on your model of tractor but most are designed in the way I will describe if the fuel tank filler is above the engine.
When the fuel tank is half full or more and you are operating on level ground, gravity will deliver fuel from the tank to the injection pump.
If tank levels are lower and further, if you are on sloped ground, the gravity fuel feed no longer works and designers incorporate lift pumps to move fuel from the tank to the injection pump.
The lift pump is usually some sort of simple mechanical pump mounted on the side of the engine. If you follow the fuel line from the bottom of the tank you will come to the lift pump which is usually before the filter but not always.

If your fuel tank is high on the tractor, I would eliminate the lift pump by connecting the in and out hoses together and then keep the fuel tank full.
Drain and refill the crankcase and then monitor the oil level. Use the tractor but just keep the fuel level high.
If the oil level stays normal then you have found the source of your problem.

Good luck
Dave m7040

I think the seal on the hydraulic pump is failed and you are pumping hydraulic fluid into the engine crankcase. Easy to fix if you can determine the correct seal to order. On my L185 I just ordered them all along with the seals and o-rings.


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One thing you could do if you suspect hydro oil is getting into the engine would be to add some oil dye to the hydo oil and see if the color changes in the motor oil. I use dye that I pick up from the Caterpillar dealer. Its hard to mistake the oil when it changes to a red color. Another thing to watch out for on some of the Kubota engines is the dipstick itself. The rubber grommet on the stick will come unglued and slide up and down the stick throwing off your measurement.

Steve mentions a good method to locate leaks.
I am not familiar with what Caterpillar would use but there are products available at amazon and most auto parts stores which use a UV or ultra violet light and special glasses.
These systems originated in the Air Conditioning business where leaks are small and hard to find and has now been made available for all vehicle systems being worked on by guys in their own shops for a reasonable price.
You add a dye, which reacts to UV light, to the crankcase, the rad, the power steering system etc. You operate the vehicle for a while and then, while wearing special yellow glasses, you shine a small flashlight which projects a UV beam. The area where the leak is happening will glow a very distinct color so you can see exactly where the leak is and not be confused with the fluid being blown unto another area.
There are different dyes for different systems. The dye for the cooling system is not good for the oil based systems.

Here is a youtube video showing this being done.
https://www.youtube.com/watch?v=mK9RqhD2OfI

This amazon UV system includes a special AC hose so you can find leaks in your AC system.

http://www.amazon.com/Mastercool-53...5295740&sr=8-1&keywords=uv+leak+detection+kit

I have not personally used the UV kit in fuel systems so others may have comments on this. Perhaps you would need to add the dye when the fuel level is low so that it is not diluted too much as it would be if you had a full tank.

Dave M7040

You could also test the drain oil and you will know exactly what's going on, if anything. https://www.amsoil.com/shop/by-prod...zers-test-kit-non-postage-paid/?code=KIT06-EA