ASE A1 Engine RepairGeneral Engine DiagnosisMedium
A technician is performing an oil pressure test on an engine. The manufacturer's specification is 10 PSI at hot idle and 40-60 PSI at 2000 RPM. The technician measures 5 PSI at hot idle and 25 PSI at 2000 RPM. Which of the following is the MOST likely cause of these readings?
- AExcessively thick engine oil
- BStuck open oil pressure relief valve
- CClogged oil filter
- DFaulty oil pressure gauge
Show answer & explanationAnswer & explanation
Correct answer: B. Stuck open oil pressure relief valve
Low oil pressure at both idle and RPM, consistently below specifications, is a classic symptom of a stuck-open oil pressure relief valve, which prevents oil pressure from building adequately by constantly diverting oil back to the sump.
Why the other options are wrong
- A. Excessively thick engine oil would generally cause higher, not lower, oil pressure readings due to increased resistance to flow.
- C. A clogged oil filter would typically cause a pressure drop across the filter, potentially triggering the bypass valve, but usually doesn't result in such low overall system pressure unless the entire system is severely restricted.
- D. While a faulty gauge is possible, the consistent pattern of low pressure at both idle and RPM strongly suggests an actual engine issue, especially if verified with a known good gauge.
Oil Pressure Relief Valve
The oil pressure relief valve regulates the maximum oil pressure in the engine by opening to divert excess oil back to the oil pan when pressure exceeds a set limit.
- Prevents excessive pressure that could damage seals and components.
- If stuck open, oil pressure will be consistently low.
- If stuck closed, oil pressure will be excessively high.
Memory trick: Oil pressure low, relief valve open, or pump's slow.