FAA Ground School Practice Test

Generally speaking, what effect does the use of carburetor heat have on engine performance?

1. Increase engine performance

2. No effect on engine performance

3. Decrease engine performance

4. Stabilize engine performance

The correct answer is: Decrease engine performance

The use of carburetor heat generally decreases engine performance. This is because carburetor heat is applied to prevent ice formation in the carburetor, which can occur when the airflow through the carburetor creates a temperature drop. While carburetor icing can lead to engine performance issues, applying carburetor heat raises the temperature of the incoming air-fuel mixture, which can reduce overall engine efficiency. When carburetor heat is used, it draws hot air from around the engine instead of cooler ambient air. This warmer air is less dense than cooler air, which means that the engine receives less oxygen for combustion. Consequently, lower oxygen levels lead to a reduction in power output from the engine. Therefore, while carburetor heat is a vital tool for maintaining engine operation and preventing ice formation, it has the side effect of reducing engine performance as it causes the mixture to become richer, leading to lower power efficiency.