* Worn Oil Pump: The most common cause. The pump's internal components (gears or vanes) may be worn, reducing its efficiency at lower RPMs. At higher RPMs, the increased engine speed helps overcome the reduced pumping capacity.
* Low Oil Level: While seemingly obvious, insufficient oil will lead to low pressure, especially at idle when the oil isn't being circulated as vigorously. Check your oil level immediately.
* Thick Oil: Using oil that's too thick (high viscosity) for the operating temperature can restrict flow, resulting in low pressure at idle. This is more likely in colder weather.
* Clogged Oil Pick-up Tube: The tube that draws oil from the bottom of the pan might be clogged with sludge or debris, restricting oil flow to the pump.
* Worn or Damaged Bearings: Worn crankshaft or camshaft bearings allow oil to leak past them, reducing the pressure available in the system. This often presents as progressively worsening low oil pressure.
* Failing Oil Pressure Sending Unit/Sensor: While less likely, a faulty oil pressure sensor could provide an inaccurate reading. However, it's less probable that it would only read low at idle. Replacing this is a relatively inexpensive diagnostic step.
* Leaking Oil Seals/Gaskets: Significant leaks can reduce the overall oil volume, leading to low pressure.
What to do:
1. Check the oil level immediately: This is the first and easiest thing to do. Low oil is a serious problem that can cause catastrophic engine damage.
2. Check the oil pressure gauge itself: Is it the original gauge, or has it been replaced? There's a small chance it is defective or incorrectly calibrated. This is less likely if it shows a normal reading at higher RPMs.
3. Inspect for oil leaks: Look for any visible signs of oil leaks around the engine.
4. Have the oil pressure tested with a mechanical gauge: This is crucial for accurate measurement. A mechanic can connect a mechanical gauge directly to the engine to bypass the possibility of an inaccurate reading from the sending unit. This will confirm if the low pressure reading is real or just a sensor problem.
Ignoring low oil pressure can lead to serious engine damage, including seizing, so addressing this issue promptly is vital. A mechanic should diagnose and repair the problem to prevent further damage.
