Oil Pressure — General Information and Troubleshooting
Normal oil pressure values for the 944 at idle and at speed, interpretation of high and low readings, and diagnosis of relief valve, pump pickup tube, and bearing failures.
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Normal Oil Pressure Values
The 944 oil pressure should run 4–5 bar at idle when the engine is cold. As the oil warms to normal operating temperature, pressure will gradually decrease to 2–3 bar at idle. At normal operating temperature and 5,000 rpm, oil pressure should read approximately 4 bar.
Oil takes longer to reach normal operating temperature than coolant — do not be surprised if oil pressure continues to decline after the coolant temperature gauge has stabilised.
Reading the Gauge
Pegged high (5 bar) or will not read below 4 bar at operating temperature: indicates a likely problem with the oil pressure sending unit, not the oil system itself.
Very occasional dip below 2 bar: can occur on very hot days after extended hard driving.
Warning: Oil pressure below 1 bar is cause for serious concern. This indicates a problem with either the oil pressure indication or the oiling system itself. Do not drive the car until the cause is determined and corrected.
Causes of Low Oil Pressure
Problems with the gauge and low-reading failures are rare; low oil pressure normally indicates an actual problem with the oiling system.
Failed oil pressure relief valve: one method of diagnosis is to remove the relief valve and briefly crank the engine to verify that oil exits the relief hole. Oil coming out confirms a relief valve problem. No oil or very little oil from the hole suggests a problem with the pump itself.
Loose crankshaft pulley bolt: the crankshaft bolt applies force to a spacer that tensions the gear driving the oil pump. If the bolt is loose, the gear will not turn the pump.
Broken oil pump pickup tube: normally caused by excessive vibration when the motor mounts are bad. The oil pan must be removed to replace the tube.
Worn main and/or rod bearings: oil pressure that tracks normally through the range but reads lower than normal throughout typically points to leaking oil pressure relief valve or worn main/rod bearings.
Oil Pump Lost Prime
If no oil pressure is indicated when the car is started, the oil pump may have lost its prime. To re-prime:
- Remove the oil filter.
- Pour oil down the centre hole of the filter mount while rotating the crankshaft counter-clockwise.
- Install a new oil filter.
- Start the car and verify oil pressure.