What causes the oil in a lawnmower engine to turn to slime and how do you fix it?

Normally your engine oil turns to slime because you are not changing it on a regular basis, or it is getting too hot because you are letting the air cooled engine sit and idle for long periods of time.

First, you need to change the oil and put in fresh oil, and if it has a filter, change it also. Run the mower for about an hour or so, mowing your lawn as you normally would. While the engine is warm, not hot, then change the oil again. While the oil is warm, it will drain out any crud that may still be there.

Remember to drain your oil about every 25 hours of operation. Or at the beginning og the mowing season, and again at least once in the season. Drain it when you get ready to put it up for the winter and put fresh oil in it for the winter.

Now, lets discuss how you operate your mower. It is torture to run your small air cooled engine at low or reduced speeds. It creates heat buildup, which fries your oil quickly. Air cooled engines need to run at top speed, for many of them depend on the dipping action of the crankshaft to pull oil up into the cylinder to cool the engine. Some even have little spoon like apertures on the bottom of the rods to pick up oil and throw it up into the cylinder. Air cooled engines will run hotter and depend on using oil to dissipate heat and keep the engine in a normal heat range. So be sure to check you oil before you start mowing, and to never let it get low. I recommend filling it to the top of the mark Full so help ensure your engine has plenty of oil to help it do its job for many years to come.