A common problem encountered with turbocharger operation is the “turbocharger oil leak”.

Often the assumption is made that the turbo is at fault. This can cause unnecessary maintenance to be performed. In many cases the “oil leak” is not a turbo problem-rather it is caused by either improper turbo installation or engine maintenance.

To fully understand what causes a turbocharger to leak oil and how to prevent it, we will cover

Oil inside the turbocharger

Turbocharger Seals

Leaks at the compressor outlet

Leaks at the turbine outlet

Engine breathers

OIL INSIDE THE TURBOCHARGER

Engine oil under pressure enters the bearing housing from the oil inlet line. This oil passes between the bearing and wheel journal surfaces where, as a result of turbulence, air is mixed with the oil and is de-pressurized.
This oil then flows by gravity through the oil drain line and into the engine sump.
Anything which prevents this draining will cause the oil to build up in the bearing housing to a height above the oil seals. Under this condition, the oil will leak out into the compressor housing and/or the turbine housing past the piston ring seals.

SEALS

The main purpose of the seals at both the compressor and turbine ends of the centre housing is to prevent the high pressure gasses from entering the centre housing and then to the crankcase! The fact that that the seals prevent oil from entering the housings is secondary.


OIL AT THE COMPRESSOR OUTLET

The air filter, as it accumulates dirt, offers an increasing restriction, causing a pressure drop across it. A partial vacuum at the compressor inlet will result. If this condition continues for any length of time, it will cause oil to be drawn from the bearing housing and into the compressor housing and induction system. Service the air filter regularly to prevent this condition.

OIL AT THE TURBINE OUTLET

Problems with the oil drain system can cause leaks to turbochargers as well. The majority of turbocharger oil leaks are recognized at the turbine (exhaust) outlet. This is because you will get an indication of oil coming out the tailpipe or leaking out the parting lines of the center housing and turbine housing. If the center housing does not drain back to the sump properly, the level of oil in the bearing housing will exceed the height of the seals and leak. Check the following conditions and correct them to eliminate the problem. Make certain that the turbo oil drain port is pointing down at no more than a 35 degree swing on either side of a vertical center-line. On gravity drain systems (no scavenge pump) ensure the drain lines slope downward with no kinks or bends to gather oil and create a blockage.
Finally, check the condition of the drain lines. Those made from a rubber-lined fabric covered hose may not cause any problems at all after running several years in one position. Even though the exterior of the hose looks fine, the rubber interior lining has become brittle. When replacing the turbocharger at any time, it is very possible that such a drain line could be disturbed and bent, causing pieces of the brittle rubber to break off inside the drain line and partially obstruct the flow of oil. To prevent this from happening, always inspect the drain line when the turbo-charger has been removed.

ENGINE BREATHERS

Oil leaks in the turbocharger may also, be the result of problems in the crankcase ventilation system. The vent or breather line may sometimes become clogged or restricted through engine operation. These conditions allow positive pressure to build up in the crankcase and restrict the oil from flowing down the drain hose and into the crank-case. This will cause oil to back up into the bearing housing and leak past the piston ring type seals.