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Turbocharger Oil Leaks
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Common sources of Turbocharger Oil Leaks (As rewritten from an turbocharger rebuilder)
Oil Inside the Turbo
Engine oil under pressure enters the bearing housing through the oil inlet supply line. The oil lubricates the bearing and journal surfaces where it picks up heat from the exhaust turbine and as a result of oil turbulence internal in the bearing, air tends to get entrained in the oil. The oil then exits the turbine bearing sump through the drain line (in many cases a gravity drain line) back to the oil reservoir (crankcase). If any thing causes a restriction to this drain line, foamy, air entrained oil will backup into the bearing housing until it is higher than the oil seals on the turbine shaft. The oil (oil mist) can leak into the compressor side of the housing and get carried into the engine under boost and get burned with the fuel mixture.
Types of Seals
The seals at both the compressor and turbine ends of the bearing housing are typically designed to prevent the high pressure gases from entering the bearing housing and then into the engine crankcase. The prevention of oil entering the compressor and turbine housings is a secondary function of the seals.
Oil at Compressor Inlet / Outlet
A too small capacity air filter (or one restricted by dirt) can allow the air velocity through an oiled filter to carry over the oil into the compressor inlet. This would be evident only on the compressor outlet. Correction is to remove the restriction at the air filter.
Oil at Compressor Outlet
A dry type filter will have increased restriction as it becomes dirty. This results in a pressure drop across the filter. Under engine loading, a positive pressure exists at the oil seal behind the compressor impeller so the pressure drop is not noticed. However, in an unloaded engine, ie idle or at low rpm, a potential exists where a partial vacuum occurs at the compressor inlet and behind the compressor impeller simultaneously. If this condition is present for any length of time, it can cause oil to be sucked from the bearing housing through the oil seal and into the compressor housing and then into the engine intake. A differential pressure gauge mounted between the air cleaner and the turbocharger is an excellent method to measure too much intake restriction.
Oil at Turbine Outlet
See 'Oil inside the Turbo' above. To correct, make sure that the drain port is pointed down at a 35 degree angle and that the drain line does not have any loops or uphill type bends. This s-type bend (loop) could cause a buildup of oil in the line preventing oil draining to the crankcase. Make sure that the crankcase is not overfilled with oil. This could result in the drain line trying to gravity drain into the oil level in the crankcase causing an increase in drain back resistance, backing foamy oil into the turbine bearings.
If the turbo has recently been replaced or the drain line moved, check to make sure that the drain line hose has not become plugged. Due to the tremendous heat generated by turbos, when old hoses are removed and reinstalled, the internals of the hose ID may fail causing blockage.
Engine Crankcase Breathers
Make sure that nothing is causing an increase in crankcase pressure (ie bad check valve on a PCV system). This would decrease the ability of the gravity drain back line to the engine crankcase.
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