Which of the following NOT listed as a fuel characteristic?

• A. Low freeze point
• B. High vapor pressure
• C. High flash point
• D. High viscosity

Answer: (D)

In choosing fuels, properties are listed that help fuel flow, atomize, and stay safe during handling. A fuel should remain fluid at low temperatures (low freeze point) so it doesn’t gel or stop flowing in cold weather. It should vaporize readily enough (adequate vapor pressure) to ensure proper combustion in the engine. It should also have a high flash point to reduce the risk of accidental ignition during storage and handling.

High viscosity, however, is not a favorable or standard listed characteristic. If fuel is too viscous, it can resist pumping, impede smooth flow through fuel lines, and hinder atomization in the injector or carburetor, leading to poorer engine performance. That’s why high viscosity isn’t listed as a desirable fuel trait, whereas the other three are the traits you expect to see.

So the choice corresponding to high viscosity is the one that isn’t listed as a positive fuel characteristic.