Getting Fuel In My Engine Oil

If you notice that your oil level is increasing and smells like raw diesel, you might be getting fuel in your engine oil. On a Yanmar YM series tractor there are really only two ways this can happen.

1- You can have a bad injector that is basically pouring raw fuel directly into the cylinder and that unburned fuel is running down beside the piston into the oil pan. This usually produces an extreme amount of fuel smoke which is gray, burns your eyes, and smells like diesel. If the leak is large enough to increase oil levels, this smoke will be extremely obvious. This will usually also create a very distinct hammering sound as the piston is trying to compress an uncompressible liquid. The only time it might not produce smoke or hammering is if that cylinder has enough damage that it can not build enough compression to ignite any of the fuel. This will usually mean a very rough running engine. 

2- The most common way fuel ends up in the engine oil is from a bad injection pump. The injection pump is mounted into the engine block and the bottom side of the pump is lubricated by engine oil.  Any fuel leaking out of the bottom side of the injection pump will run right into the engine oil. Injection pumps can leak while running and also just by gravity feed from the tank when they are parked. These pumps do not typically have o-rings or seals that are user serviceable and, if you take one apart, it will need to get re-calibrated by an injection shop (using expensive and specialized tools).  You will usually need to send the pump off to get rebuilt or just replace it if it is leaking.