Whipping it like eggs becomes frothy, which might make a good start to a delicious omelette, but not so much for viscosity. When too much oil is added, the level in the oil pan becomes too high. That allows a fast-moving lobed rod called the crankshaft to come into contact with the oil and essentially aerate it. The result is a foamy, frothy substance that cannot properly lubricate the engine.
Specifically for a diesel, however, excess oil in the crankcase can cause it to be forced up past the piston rings and into the combustion chamber.
This is just a sample. A short cursory google will give examples from people smarter than me on the subject.