Mercedes-Benz W124 oil pressure and oil pressure gauge
What is the normal oil pressure of a Mercedes-Benz W124?
When hot at idle the pressure is often about 1 bar or a little below, and the manufacturer's lower limit is 0.3 bar. When revs are raised the pressure must rise quickly, to about 3 bar at 2000 rpm. When cold the pressure is higher. Exact readings vary between cars.
How do I check whether the oil pressure gauge or sender is faulty?
The surest way is to connect a mechanical pressure gauge in place of the sender. If the gauge reads zero or full already before starting, the fault is often the sender or its wire. The sender resistance is 10 ohms at 0 bar, 69 at 1 bar, 129 at 2 bar and 184 ohms at 3 bar, with a variation of a few ohms allowed.
What can cause a real drop in oil pressure?
A clogged oil filter can prevent the pressure from rising, and debris at the pressure relief valve can keep the pressure low. If the pressure drop comes with a loud knocking noise, the cause may be bearing damage, in which case the car should not be driven but belongs in a workshop.