ASE A1 Engine RepairEngine Block AssemblyEasy
An engine suffers from persistent low oil pressure despite a new oil pump being installed. Upon disassembly, the technician finds that the main bearings show signs of severe wear and have a larger than specified oil clearance. Which of the following is the MOST likely reason for the low oil pressure?
- AExcessive oil clearance in the main bearings
- BIncorrect oil viscosity (too thick)
- CClogged oil filter
- DExcessive oil pressure relief valve spring tension
Show answer & explanationAnswer & explanation
Correct answer: A. Excessive oil clearance in the main bearings
Excessive oil clearance in the main bearings allows too much oil to escape from the bearing journals, reducing the pressure in the rest of the lubrication system. This is a common cause of low oil pressure, even with a good oil pump.
Why the other options are wrong
- B. Incorrect oil viscosity (too thick) would typically increase oil pressure, especially when cold, or make it harder for the pump to move, not cause persistently low pressure after a new pump.
- C. A clogged oil filter would restrict oil flow, potentially causing low pressure, but the main bearing wear indicates a different primary issue.
- D. Excessive oil pressure relief valve spring tension would cause HIGH oil pressure, not low.
Bearing Oil Clearance & Oil Pressure
The gap between a bearing and its journal, which when excessive, allows too much oil to escape, leading to a significant drop in engine oil pressure.
- Oil clearance forms the oil film
- Excessive clearance reduces hydraulic resistance
- Leads to low oil pressure and potential engine damage
Memory trick: Loose bearings, low pressure, lubrication stress.