Low Oil Pressure – Troubleshooting The Causes Of Low Oil Pressure

Engine oil is used to cool and lubricate bearing and machined surfaces.

Without oil pressure an engine will experience extreme internal engine damage due to heat caused by friction.

A good place to start troubleshooting low oil pressure conditions is at the dipstick.

Check the oil level to see that it is at the proper level.

Common Symptoms Of A Low Engine Oil Level:

  • Warning Light, The simplest indicator of a low oil level is when the oil warning light activates.
  • Smell of Burning Oil, This burning smell could be from an oil leak onto the hot components of your engine.
  • Knocking Sounds, The reason is because there is less oil to lubricate the engine parts.
Engine Oil Level
Engine Oil Level

A Low Oil Level Could Be The Engine Leaking Or Burning Oil

If the engine is leaking oil, install new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals could be worn. Also, On high mileage engines you may have worn piston rings or cylinders. A wet compression test and/or cylinder leak down test will tell you what parts may be worn out. If this is the case you will be visiting your local machine shop for engine repairs.

Engines Are Built To Use A Certain Viscosity Of Engine Oil

Heavier viscosity oils such as 20W-50, straight 30W and 40W may help maintain good oil pressure in hot weather, but are too thick for cold weather driving and may cause start-up lubrication problems especially in overhead cam engines. Light viscosity oils, on the other hand, such as straight 10W or 5W-20 may improve cold weather starting and lubrication, but may be too thin for hot weather driving to maintain good oil pressure. That is why most OEMs today recommend 5W-30 for year-round driving in modern engines.

Oil Pressure Light, Gauge And Sending Unit

Oil Pressure Sending Unit
Oil Pressure Sending Unit

If the oil level is okay, the next thing to check would be the oil pressure sending unit.

The Three Most Common Symptoms Of A Faulty Oil Pressure Switch Or Sensor:

  • Repeated Blinking from the Oil Pressure Light
  • The Wrong Reading Shows on the Oil Pressure Gauge
  • The Oil Pressure Light Activates

Disconnect the unit and check the warning lamp or gauge reading. If the warning light remains on with the sending unit disconnected, there is probably a short to ground in the warning lamp circuit. Likewise, if there is no change in a gauge reading the problem is in the instrumentation not the engine.

Bad oil pressure sending units are quite common, so many technicians will replace the unit without checking anything else to see if that cures the problem. This approach might save you some time, but it is risky. Unless you measure oil pressure directly with a gauge attached to the engine you have no way of knowing if pressure is within specifications or not. Most warning lamps won’t come on until you have dangerously low oil pressure (less than 4 or 5 lbs.). So don’t assume the absence of a warning lamp means oil pressure is okay, especially if the engine is making any lifter or bearing noise.

If a check of oil pressure reveals unusually low oil pressure readings, check the oil filter. It is possible the oil filter might be plugged with gunk. Replace the  oil filter and see if that makes a difference.

Finally, Checking The Bottom End

Engine Bottom End
Engine Bottom End

The next step would be to drop the oil pan and check the oil pump pickup screen. Check to see that the pickup tube is properly mounted and positioned, firmly attached to the oil pump (no leaks) and is not obstructed.

If the oil pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is the only option.

If the pump appears to be okay, the next step would be to measure the rod and main bearing clearances. Check the clearances on the main bearing closest the pump (since this has the greatest effect on pressure), and clearances on the furthest rod bearing (since this will show the greatest wear). If the crankshaft bearings are worn, they will need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals are worn, the crankshaft will have to be reground or replaced.

Other checks might include camshaft, cam bearings and lifters. Remember, excessive clearances or leaks anywhere in the engine’s oil supply system can contribute to low oil pressure.

Low Oil Pressure, Conclusion

Oil pressure depends on several critical factors, such as:

  • Oil supply
  • Engine oil type
  • Engine condition
  • Oil pump condition
  • The weather
Low Oil Pressure
Low Oil Pressure

While many older oil pressure gauges were actual hydro-mechanical gauges, warning lights and most modern gauges are electrical or electronic.

When investigating low oil pressure problems, the best way to test actual oil pressure is with a mechanical oil pressure gauge.

Oil pressure can be checked at the sending unit passage with an externally mounted mechanical oil pressure gauge.

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DannysEnginePortal.com Is The Premier Automotive Engine Troubleshooting Resource Site. DannysEnginePortal.com Shares Information On Engine Troubleshooting, Engine Rebuilding, Engine Repair Tips, Tech Info, Basic Machining, Automotive Testing, In Addition To Possible Solutions.