FAA Powerplant Written Practice Test

What defect is likely to cause a hot spot on a reciprocating engine cylinder?

1. Excessive oil in cylinders

2. Too much cooling fin area broken off

3. Weak magneto spark

4. Low fuel flow to the engine

The correct answer is: Too much cooling fin area broken off

A hot spot on a reciprocating engine cylinder typically occurs due to localized overheating, which can be exacerbated by insufficient cooling. In this context, the loss of cooling fin area is significant, as the cooling fins are designed to dissipate heat from the engine cylinders. If there is too much cooling fin area broken off, there would be less surface area available for heat dissipation. This reduction in cooling capability can lead to an increase in temperature in the affected area of the cylinder, resulting in a hot spot. Excessive oil in the cylinders can lead to different issues, such as oil fouling or increased engine wear, but it does not directly correlate with the formation of hot spots in the same way that reduced cooling capacity does. A weak magneto spark might lead to poor ignition or incomplete combustion but wouldn't necessarily create a localized heat issue reflective of a hot spot. Low fuel flow might cause power loss or an overly lean mixture, eventually impacting engine operation, but again, it does not directly create the localized overheating characteristic of hot spots. Therefore, the issue of broken cooling fins directly ties to the thermal management of the engine cylinder, making it the most plausible choice for causing a hot spot.