A thin film of oil on the lobes of a Roots-type blower indicates __________.

Correct Answer: Option D — leaking rotor bearing oil seals

Roots-type blowers rely on close tolerances without internal lubrication. Detecting an oil film on the rotor lobes indicates that the carbon or labyrinth oil seals separating the gearcase from the air chamber have failed, allowing lubricating oil to bypass into the scavenge air stream.