The only thing that stands between your engine and death is oil. Did you know (I was shocked when I leaned), that the major turning loads in your engine are NOT supported by ball bearings, or roller bearings, or anything else that rolls? All the main loads are carried by a round part stuck into a round hole, with room for just a microns-thin film of oil between the shaft and the hole. That's it. A thin film of oil. And how those parts suffer if there are bits of dirt or metal in that oil. And may the engine gods have mercy on your engine's soul if the oil is gone. Metal rubs on metal, heat builds up, the metal expands and soon the gap is gone and the shaft welds itself into the hole...and that's the end. So...dirty oil and low oil...bad, bad, bad. But what happens if there is too much oil? Mechanical sickness and engine death are ready and waiting for you there too. Let me count a few of the ways...
Why do I bring this up? This year I have had three over-oiled machines come into the shop. One wouldn't turn at all. One wouldn't run. The third, fortunately for the owner, had already died and the engine had been over-filled in a misguided attempt to revive it, so it was never re-started with too much oil, fortunately for him.
The basic problem is that excess oil goes places it shouldn't. More on that in a moment. The other problem, is that with most engine designs, excess oil gets splashed excessively...to the extent that it becomes foamy... foamy oil doesn't flow, and cannot go where it is needed...which is just as bad as having too little oil. How does this happen? The connecting rods that connect the pistons to the crankshaft travel down into the upper reaches of the oil pan at the bottom of the engine. If they hit the oil, it splashes and becomes filled with air bubbles...it foams. So, too much oil puts oil was where it was not supposed to be (too high in the oil pan) and foamy oil is the result.
You recall I mentioned the over-oiled engine that would not turn? That engine had a horizontal cylinder. It pointed sideways rather than mostly up. It was a lawnmower and most lawnmowers are designed that way. In that case, while the engine was off, the excess oil seeped past the piston rings and filled up the cylinder. The cylinder is not supposed to have anything inside it but air and a few molecules of fuel. When the owner went to start the engine, the piston could not rise in the cylinder because the cylinder was full of oil. Air will compress; liquids, including oil, will not. The piston might as well have been welded to the cylinder walls. It would not budge...until we pulled out the spark plug and drained out the oil stuck inside the cylinder. After that, we drained the oil down to normal level, cleaned, dried and reinstalled the spark plug...and fired it right up. The next guy was not so lucky.
The next engine would turn, but wouldn't run. The plug was completely fouled (caked with residue burned carbon from burning too much oil), the air cleaner was soaked with oil and the exhaust was dripping oil. In this case, the cleanup required was a little more extensive, but in the end, the result was the same. After draining out the excess oil, getting a new clean filter and a clean plug, she fired right up. She smoked like crazy as the excess oil in the exhaust burned off, but after running for five minutes, the excess oil had cooked off, the smoke stopped, and she ran like a top.
So, how does one prevent this ugly problem? First, read. Read the manual. These days, a little Google searching will turn up reliable documentation on your engine that will tell you how much, and what sort of oil your engine needs. Next, check the dipstick. Most engines have a dipstick, and those that do not generally have a sight window that allows you to see the oil level from outside the engine.
After the engine has been off for at least a few minutes, sitting on level ground, pull the stick, wipe it clean, (like the one you see above), stick it back where it came from, and pull it out again. When you do, you should see oil on the stick, somewhere between the ADD and FILL marks. Too low on the stick, add oil. Too high on the stick, like you see in this next photo, (You see the stick is wet right up to the L's in FULL, way past the point of the FULL arrow)...
...then it is time to get rid of some oil. Drain some or use something to suck it out (something besides your mouth, like a plastic tube and a turkey baster!). Once your oil level is right, your mechanical life can go back to normal.