If your vehicle is showing engine block is covered in thick, greasy grime, here are the most likely causes and the parts you'll need to fix each one.
The rubber or cork gasket sealing the top of the engine degrades and hardens over time. This allows engine oil to seep out and run down the sides of the block, where it collects road dust and turns into thick grime.
Oil spilled during a routine oil change or a loosely installed oil filler cap can blow back across the engine. Over time, this coats the block in a greasy residue.
A blocked PCV valve traps blow-by gases inside the engine, creating excess crankcase pressure. This pressure forces oil vapors out through various gaskets and seals, coating the engine block in oil.
The seal between the bottom of the engine block and the oil pan fails, causing oil to seep out. Driving wind blows this seeping oil backward, coating the lower half of the engine in grime.
Seals at the front of the engine wear out, allowing oil to leak down the front of the block. The engine cooling fan and driving wind blow this oil backward across the entire engine block.
The sensor that monitors engine oil pressure can develop an internal leak or a leak at its threads, spraying a fine mist of pressurized oil onto the side of the engine block.
The large seal at the back of the engine crankshaft fails, causing a heavy oil leak. This coats the rear of the engine block and the transmission bellhousing in thick, wet grime.