Whereas more blunt, less complex emotions such as anger and fear bear greater likeness to fuel, the nature of suffering seems to bear the characteristics of an engine. Productive people -- for better or worse -- have learned to burn emotional fuels very cleanly, deriving a great deal of compression and energy, and thereby velocity, by attuning their internal emotional engines to whatever mixture is present in their lives in relative abundance.
Suffering, however, seems to be decidedly less a producer than a consumer of fuel. Furthermore, as engines go, it is highly inefficient, converting most of the value of its fuel to unrecoverable heat energy rather than usable motion. It shares this wasteful and inefficient nature with many other engines possessing similar properties and applications; virtue is a prime candidate for comparison, being similarly noisy, cumbersome, difficult to place in parallel with other machinery, undependable as a primary source of energy, and for aesthetic reasons best kept hidden from view of passersby.
It is unclear what, aside from random thermal energy, such an engine could produce, if not self-righteousness -- or perhaps self-wrongeousness. Both are already present in abundance; the first is characterized as a incombustible social pollutant; the other, a vigorous social retardant.