Question 63 QMED03 - Oiler

The Correct Answer is C. A coarse screen wire mesh strainer is normally found on the **pump suction line** (Option C) of a diesel engine lubrication system. This placement serves as the first line of defense, often called a "sump strainer" or "suction strainer," designed to protect the oil pump itself. The strainer prevents large debris (such as metal shavings, gasket pieces, or large contaminants that might settle in the oil sump/pan) from entering and damaging the precision components of the oil pump (like gears or rotors), which are highly susceptible to damage from large particles. ### Why the Other Options are Incorrect: **A) gravity tank inlet line:** While some systems might have strainers here, modern high-pressure diesel lubrication systems typically draw oil from a sump or wet/dry reservoir directly to the pump. The gravity tank is more common in fuel systems or older, non-pressurized lube systems. In a standard pressurized diesel lube system, the primary coarse strainer location is before the pump. **B) pump discharge line:** The pump discharge line is under high pressure. Placing a coarse strainer here is inefficient and often counterproductive. After the pump, the oil passes through the primary oil filter (which contains the fine filtration media necessary for cleaning the oil), often followed by an oil cooler, and then to the engine bearings. The debris that the coarse strainer removes must be caught *before* the pump. **D) filter bypass return line:** The filter bypass line is used when the main (fine) filter is clogged. Oil flows through this line unfiltered to ensure the engine still receives lubrication, rather than starving it of oil. While this line might technically "return" oil, placing a coarse screen here serves little protective function; the critical protection (pump and engine bearing protection) is handled elsewhere. The coarse screen must be upstream of the pump to protect it.