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Where coolant absorbs heat in a liquid-cooled engine

Aviation Mechanic Powerplant (AMP) practice question 13 of 13 on Reciprocating Engine Induction and Cooling Systems. ACS element AM.III.J.K10 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONIn a liquid-cooled reciprocating engine, where does the coolant pick up the excess engine heat?

  1. AIn the radiator ahead of the cylinders
  2. BIn water jackets around the cylinders
  3. CIn passages inside the cylinder fins
Show the answer and explanation

Correct answer: B. In water jackets around the cylinders

  • A — incorrect The radiator or heat exchanger dissipates heat to the airflow after the coolant has already absorbed it.
  • B — correct In a liquid-cooled engine, water jackets around the cylinders circulate liquid coolant that takes away the excess heat.
  • C — incorrect Cooling fins are the air-cooled method of transferring heat to the airstream and do not carry coolant.

BACKGROUND

Excessive heat is undesirable in both reciprocating and turbine aircraft engines, and without a means of removing it, major damage or complete engine failure would occur. The vast majority of reciprocating engines are air cooled, but some diesel liquid-cooled engines are available for light aircraft. In a liquid-cooled engine, water jackets around the cylinders circulate liquid coolant that takes away the excess heat. That heat is then dissipated by a heat exchanger or radiator using airflow. Stated generally, reciprocating engines are cooled either by passing air over fins attached to the cylinders or by passing a liquid coolant through jackets that surround the cylinders.

STUDY TIP

Separate the two steps: the jacket absorbs heat from the cylinder, and the radiator gives it up to the air. Air-cooled engines do the same two jobs with fins alone.

KEY POINTS

  • Liquid coolant absorbs cylinder heat in water jackets surrounding the cylinders.
  • A heat exchanger or radiator then dissipates that heat into the airflow.
  • Air-cooled engines transfer heat through cylinder fins instead of coolant jackets.

SOURCES

  • amp-powerplant/ch06.txt "Engine Cooling Systems"
  • amp-powerplant/ch06.txt "Turbine Engine Cooling"
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MORE ON RECIPROCATING ENGINE INDUCTION AND COOLING SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.