Losing oil pressure in an engine can be disastrous. If the oil warning light comes on, a driver or pilot must ascertain if it is truly an engine malfunction, or if the oil pressure sending unit is malfunctioning. By reading the signs, you can determine if it's a bad sender or if something else is the culprit.
When driving or flying, the needle in the oil pressure gauge should be in the normal range. If it drops suddenly to zero, you know something is wrong. According to the University of Wisconsin, a malfunctioning oil pressure gauge may indicate a defective oil sending unit, a defective gauge or a break in the wiring harness.
Erratic oil pressure is another sign that the sending unit may be bad. The needle in the pressure gauge may start out in the normal range when the engine is running but suddenly start to act erratically. The needle may jump around from zero pressure to maximum pressure then back to zero wildly. Or it will shake and jump around throughout the entire range.
Excessive oil pressure is another sign the sending unit is bad. The needle in the oil pressure gauge will rise suddenly to maximum and stay there. The pressure sending unit is then stuck in the "open" position, sending a false signal that the pump is overworking or a pressure relief valve is blocked shut.
If the oil pressure gauge shows any abnormal readings, such as excessive oil pressure or the needle bouncing around, all engine systems should be tested by a qualified technician. If the sending unit is indeed bad, it is inexpensive and easily replaced. If your car does not have an oil pressure gauge but only a dashboard warning light, the car should be tested by a qualified technician who can determine where the fault lies using diagnostic equipment.
