Overfilling your engine with oil is as bad as running low on lubricant. But what if you filled it properly yet over time your dipstick begins to show you have more oil than you started with? Your engine could be “making oil,” mechanic slang for fluid intrusion of the crankcase.
Often, making oil results from gasoline blowing by the piston rings. Excess fuel could be getting into the crankcase due to a leaking carburetor or injector or due to a bad intake manifold. If excess gas is the culprit, you can usually smell it on the dipstick.
Check your oil regularly. This includes boaters running four-stroke outboards, some of whom still operate in “two-stroke mode” (“tilt-it-down-and-go” ) and don’t check the oil before slipping the lines.
In any event, discovering an overfilled crankcase means not running the engine and diagnosing the situation immediately.