A restricted air filter in a diesel engine will most likely cause which of the following?

• A. Loss of power
• B. Increased fuel consumption
• C. Higher exhaust temperatures
• D. Hard starting

Answer: (A)

When the air entering a diesel engine is restricted, there’s less oxygen available for combustion. Diesel power is driven by the amount of air that can be drawn into the cylinders, because the injected fuel must burn with that air. With less air to burn, the engine can’t release as much energy per cycle, so overall power output falls. That drop in power is the most direct and noticeable consequence, which is why loss of power is the best answer. While some other symptoms can occur in extreme cases, a restricted intake doesn’t typically cause higher fuel consumption, and hard starting or much higher exhaust temperatures are not as consistently linked to a clogged filter as the evident power loss.