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High oil consumption after overhaul

Aviation Mechanic Powerplant (AMP) practice question 2 of 9 on Engine Lubrication Systems. ACS element AM.III.G.K7 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONHigh oil consumption is experienced after a newly overhauled piston engine is placed in service on ashless dispersant oil. How can this condition be avoided?

  1. AUse mineral oil until consumption stabilizes
  2. BAdd preservative oil at the next oil change
  3. CChange to a higher-viscosity ashless dispersant oil
Show the answer and explanation

Correct answer: A. Use mineral oil until consumption stabilizes

  • A — correct Additives in some ashless dispersant oils may retard the break in of the piston rings and cylinder walls, and the condition is avoided by using mineral oil until normal oil consumption is obtained, then changing to ashless dispersant oil.
  • B — incorrect Preservative oil protects new engines from rust and corrosion at the factory and is removed at the end of the first 25 hours; it is not a remedy for high consumption.
  • C — incorrect Raising the viscosity grade does not address the cause, which is that the additives are retarding break in of the rings and cylinder walls.

BACKGROUND

If ashless dispersant oil is used in a new engine or a newly overhauled engine, high oil consumption might possibly be experienced. The additives in some of these ashless dispersant oils may retard the break in of the piston rings and cylinder walls. This condition can be avoided by the use of mineral oil until normal oil consumption is obtained, then changing to the ashless dispersant oil. Mineral oil should also be used following the replacement of one or more cylinders, or until the oil consumption has stabilized. Straight mineral oil grades 65, 80, 100, and 120 contain no additives except a small amount of pour point depressant and an antioxidant, which is why they are used during the break-in period.

STUDY TIP

Link break-in to straight mineral oil and normal service to ashless dispersant oil, and apply the same rule after cylinder replacement. In every case, refer to the manufacturer's information when oil type or time in service is being considered.

KEY POINTS

  • Ashless dispersant oil in a new or freshly overhauled engine can cause high oil consumption.
  • Its additives may retard break in of the piston rings and cylinder walls.
  • Use straight mineral oil until consumption stabilizes, then change to ashless dispersant oil.

SOURCES

  • sources/amp-powerplant/ch06.txt "Reciprocating Engine Lubricants"
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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.