If synergies deriving from automotive partnerships are so great -- as Fiat Chrysler boss Sergio Marchionne posits -- why is Nissan's return on capital so poor? That's the question asked by Deutsche Securities analyst Kurt Sanger.

Nissan CEO Carlos Ghosn touts his Renault-Nissan Alliance as a stellar example of a tie-up that works. Yet, judging by Marchionne's standards, it hardly does.

In his plea for consolidation, Marchionne says that to earn their keep, auto companies need a return on the cost of capital of at least 9 percent. So Sanger looked at the return on invested capital at Japan's Big 3: Toyota, Honda and Nissan.