1 Oil pressure switch at the end of the lubrication circuit
2 The bypass valve opens when the oil filter is clogged
3 The pressure reducing valve opens at increased pressure
The oil pump takes oil through the oil intake 6 from the oil sump and supplies it to the main oil filter. There is a pressure-reducing valve at the outlet of the oil pump. The valve opens when the pressure is too high and some of the oil flows back into the oil sump.
Oil enters the main channel through the central axis of the oil filter cartridge. When the oil filter is clogged, the bypass valve opens and ensures the supply of unfiltered oil to the main channel.
The main channel branches off into the lubrication channels for the crankshaft bearings 2. Through the inclined holes in the crankshaft, the oil flows to the connecting rod bearings and from there is sprayed onto the piston pins and cylinders.
At the same time, engine oil is supplied through inclined channels to the cylinder head to the camshaft bearings, rocker arm shafts and rocker arm supports.
Checking oil pressure
- Warm up the engine while driving. When the operating temperature is reached, the oil should be about 80 degrees. Check the oil level.
- Disconnect the electrical wire from the oil pressure switch and unscrew the oil pressure switch. On the M20 engine, the oil pressure switch is located under the right engine beam, so you must first remove the engine sump. On M30 engines (530i, 535i) it is located under the expansion tank of the cooling system on the cylinder head, which should first be cleaned and put aside with the hoses connected. On M40 and M50 engines, open the oil filter cover to allow the oil to flow back into the engine, and then unscrew the switch from the filter housing. The location of the switch on diesel engines: on top of the oil filter cover.
- Screw the appropriate pressure gauge into the hole of the oil pressure switch.
- Start the engine and let it idle. The oil pressure should be about 0.5-2.0 bar.
- Increase engine speed to 5000-6000 rpm. Oil pressure should be at least 4-6 bar.
- Screw in the pressure switch with a new ring and tighten to a torque of 35 Nm.
- In case of deviations from the specified value, see the table for diagnosing faults in the lubrication system.
