In contrast to other parts of the engine, turbochargers do not have radial oil seals made of elastomer material. This is because of the high temperatures and high engine speeds (up to 330,000 rpm) they are subject to.
A labyrinth seal is located behind the turbine and compressor impeller which not only inhibits escape of engine oil, but also the entry of compressed air and hot exhaust gases into the bearing housing. The gas pressures at the turbine impeller and compressor impeller end prevent engine oil from escaping. The washers on the turbocharger shaft have the effect of forcing engine oil escaping from the bearing positions out from the shaft by centrifugal force. Engine oil escaping from the radial bearings as well as intake air and exhaust gases that find their way into the inside of the turbocharger are taken back to the oil pan via the return line.
If the turbocharger is losing engine oil via the intake or exhaust gas port, this usually means the pressure equilibrium is impaired due to problems with the oil/gas return line.
Reasons for oil leakage:
- Blocked, kinked, constricted or carbonised return line
- Oil level too high
- Internal pressure in crankcase too high due to excessive wear on pistons, piston rings and cylinder bores (excessive blow-by gases)
- Internal pressure in crankcase too high due to crankcase ventilation failure
Note:
Due to the much more widespread use of turbocharged engines, oil consumption caused by unfavourable turbocharger operating conditions occurs much more commonly than in the past.
1 Fresh air inlet
2 Compressor impeller
3 Fresh air outlet (compressed)
4 Axial shaft bearing (thrust washer)
5 Oil supply connection
6 Radial shaft bearing
7 Return side
8 Turbocharger shaft
9 Turbine impeller
10 Exhaust gas outlet
11 Exhaust gas inlet