ASE A1 Engine RepairGeneral Engine DiagnosisHard
A technician is performing an oil pressure test on an engine. The manufacturer's specification is 40-60 psi at 2,000 RPM (hot). The technician measures 25 psi at 2,000 RPM (hot). Which of the following is the MOST likely cause?
- AA faulty oil pressure sending unit
- BWorn main or connecting rod bearings
- CA clogged oil filter
- DAn engine that is running too cold
Show answer & explanationAnswer & explanation
Correct answer: B. Worn main or connecting rod bearings
Low oil pressure at operating temperature, especially at higher RPMs, is a strong indicator of excessive internal engine clearances. Worn main or connecting rod bearings create larger gaps, allowing oil to escape more easily and reducing overall system pressure.
Why the other options are wrong
- A. While a faulty sending unit can give false readings, the technician is performing a direct mechanical test, ruling out the sending unit as the cause of *actual* low pressure.
- C. A clogged oil filter would typically cause the bypass valve to open, maintaining pressure, or in severe cases, could restrict flow but usually doesn't directly cause a significant, sustained low pressure reading at engine bearings.
- D. An engine running too cold would typically have *higher* oil pressure due to the oil being thicker, not lower.
Low Oil Pressure Diagnosis
Low oil pressure indicates a problem with the lubrication system, often pointing to excessive clearances within the engine or a faulty oil pump.
- Common causes: Worn engine bearings, faulty oil pump, excessive oil dilution.
- Consequences: Increased engine wear, potential catastrophic failure.
- Symptoms: Oil pressure warning light, engine noise (knocking/tapping).
Memory trick: Low pressure, hot and fast, bearings won't last.