This causes increased crank case pressure which creates an increase in pressure in the sump pushing the oil back up the oil return pipe. This effectively blocks the oil return pipe so the oil entering the turbo through the oil feed pipe cannot escape out the oil drain pipe. As it backs up it is forced out the turbo sideways past the piston rings (seals) into both the turbine housing (exhaust housing) and compressor housing (Air intake housing).

As the build up of oil carbonises around the vanes they can become what people refer to as ‘sticky’ vanes which can cause them to operate erratically. The driver may experience issues with the turbo boosting and the vehicle smoking. In some cases the outcome is a destroyed turbo.