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Coolant additives as a source of chromium in oil

Aviation Mechanic Powerplant (AMP) practice question 3 of 13 on Reciprocating Engine Induction and Cooling Systems. ACS element AM.III.J.R3 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONOil analysis reports chromium in an engine oil sample. Besides chromed parts such as rings and liners, what is another primary source of chromium?

  1. ATetraethyl lead in the fuel
  2. BCoolant additives
  3. CBronze bushings and washers
Show the answer and explanation

Correct answer: B. Coolant additives

  • A — incorrect Tetraethyl lead contamination is the usual source of lead, not chromium.
  • B — correct The primary sources of chromium are chromed parts such as rings and liners and some coolant additives.
  • C — incorrect Bronze parts such as rocker arm bushings, wrist pin bushings, and thrust washers show up as copper.

BACKGROUND

Oil analysis identifies wear metals and traces them back to the engine areas that are wearing or failing. Iron indicates wear from rings, shafts, gears, the valve train, cylinder walls, and pistons in some engines. Chromium comes primarily from chromed parts such as rings and liners and from some coolant additives, which is why the chemistry of a liquid cooling system matters when interpreting a sample. Nickel is a secondary indicator of wear from certain bearings, shafts, valves, and valve guides, and aluminum indicates wear of pistons, rod bearings, and certain bushings. Lead comes mostly from tetraethyl lead contamination, and copper from bearings, rocker arm bushings, wrist pin bushings, thrust washers, and other bronze parts.

STUDY TIP

Learn the metal-to-source list as pairs, and remember that chromium has a non-wear source in coolant additives, so a coolant leak can be mistaken for part wear.

KEY POINTS

  • Chromium in oil comes from chromed parts and from some coolant additives.
  • Lead is traced mostly to tetraethyl lead contamination.
  • Copper points to bronze parts such as bushings and thrust washers.

SOURCES

  • amp-powerplant/ch06.txt "Typical Wear Metals & Additives"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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.