1 Oil pressure switch at the end of the lubrication circuit
2 The bypass valve opens when the oil filter is clogged
3 Pressure reducing valve opens at high 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 part of the oil flows back into the oil sump.
Oil enters the main channel along the central axis of the oil filter cartridge. When the oil filter is clogged, the bypass valve opens and supplies unfiltered oil to the main channel.
Lubrication channels for crankshaft bearings 2 branch off from the main channel. Oil flows through inclined holes in the crankshaft to the connecting rod bearings and from there it is sprayed onto the piston pins and cylinders.
At the same time, through inclined channels, engine oil is supplied to the cylinder head to the camshaft bearings, rocker shafts and rocker arm supports.
Oil pressure check
- Warm up the engine while driving. When the operating temperature is reached, the oil should have a temperature of about 80 degrees. Check 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 pan. On M30 engines (530i, 535i) it is located under the expansion tank of the cooling system on the cylinder head, which should be pre-shined and set aside with the hoses connected. On M40 and M50 engines, open the oil filter cover to allow oil to drain back into the engine, and then unscrew the switch from the filter housing. Location of the switch for diesel engines: on top of the oil filter cover.
- Screw a suitable pressure gauge into the oil pressure switch hole.
- Start the engine and leave it to idle. The oil pressure should be around 0.5-2.0 bar.
- Increase engine speed to 5000-6000 rpm. Oil pressure must be at least 4-6 bar.
- Screw in the pressure switch with a new ring and tighten to 35 Nm.
- In case of deviations from the set value, see the table for diagnosing malfunctions of the lubrication system.