Differential covers 101
PU Truck mag That answered a lot of my questions about these covers. Extra large ones may not make a lot of sense because they disturb the oil flow in the housing.
Forum Discussion
OEMs add them because it is a "monkey see-monkey do" business. Old Joe goes to a dealership for a new truck, sees a fancy diff cover. "Hey that's neat". Then goes to another make's dealership, another fancy diff cover, then to a 3rd dealership, "oh no, plain jane diff cover. But wait, next load of trucks at the 3rd dealership comes of the carrier truck, has fancy diff covers. Truck manufacture that supplies dealership 3 realizes they fell behind in the "fluff market" so they added them. And as far as a manufactures' cost on doing the R&D on a cover, the customer pays for it anyway. JMHO
