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Oil Leaks

Causes and Cures of Turbocharger Oil Leaks

A common problem encountered with turbocharger operations 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 most cases the oil leak is not a turbo problem; rather it is caused by either improper turbo installation or engine maintenance. We feel that if most people understand that most turbocharger leaks are caused by non-turbocharger problems, much unnecessary maintenance, downtime and expense could be saved. To fully understand what causes a turbo to leak oil and how to prevent it, we will cover:

-Oil inside the turbocharger

-Leaks at the compressor / turbine outlet

-Piston ring seals versus no seals

-Leaks in the compressor / carbureted engines

-Leaks at the compressor inlet / outlet

-Engine Breathers

-Leaks at the compressor outlet

-Internal Crankcase ventilation

Inside The Turbo:
Engine oil under pressure enters the bearing housing from the oil inlet line. This oil passes between the bearing and journal surfaces where, as a result of turbulence, air is mixed with the oil. The oil leaves the bearings looking somewhat like a "brown whipped cream", then falls by gravity to the sump at the bottom of the bearing housing. This foamy oil then flows by gravity down the oil drain line and into the engine sump. Anything which prevents this gravity draining will cause the foamy 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 and turbine housing past the piston ring seals through the piston ring gap.

Type of Seals:
The main purpose of the seals at both the turbine and compressor ends of the bearing housing is to prevent the high pressure gases from entering the bearing housing and then to the crankcase! The fact that the seals may aid in preventing oil from leaking into the turbine and compressor housings is secondary. Some turbochargers have been manufactured without a piston ring seal type seal on the turbine end.

Oil at Compressor Inlet/Outlet:
Some leaks are the result of air cleaner problems, a too small capacity or dirty oil bath air filter will allow the air velocity through the oil in the cleaner to carry oil into the compressor inlet. This type of leakage will show only at compressor outlet.
Solution: correct this type of leak by either servicing the oil bath filter by removing and steam cleaning both upper and lower halves, of installing a larger unit.

Oil at Compressor Outlet:
A dry type filter, as it accumulates dirt, becomes increasingly restricted and causes a pressure drop across it. a partial vacuum at the compressor inlet will result. This will not affect the engine under load because a positive pressure exists at the seal behind the compressor impeller. During engine idle or extremely low load, a partial vacuum occurs at the compressor inlet and behind the compressor impeller simultaneously. If this condition continues for any length of time, it will cause oil to be sucked from the bearing housing, through the seal, and into the compressor housing and eventually into the pipe between the compressor and intake manifold. Too small of an air filter will cause the same problem. The solution is simple: a commercially available gauge mounted between the air cleaner and the turbocharger will signal when the inlet restriction is too great. To prevent the air intake restriction from becoming too excessive, service the unit on a regular basis. If the air filter capacity is too small, install a larger unit

Carbureted Engine Compressor Leaks:
Turbochargers operating on carbureted engines where the carburetor is mounted upstream of the compressor should be equipped with a mechanical type seal on the compressor end of the turbocharger. This type of seal will not allow oil to pass through to the compressor even though a sudden closing of the carburetor throttle will cause a high vacuum at the compressor discharge. Any compressor-side oil leaks in Turbos equipped with this type seal would indicate that the seal was damaged, incorrectly installed, or is defective. Replacement of the seal corrects the problems.

Oil at Turbine Outlet:
Problems with the oil drain system can cause leaks to appear in the turbo. When oil leaks appear at the turbine outlet, it usually indicates a problem in the oil drain system. Something has caused the oily foam to build up in the bearing housing to a height above the seals. Check the following items and correct them to eliminate the problem. Make certain that the turbo drain port is pointing down at not more than a 35 degree swing on either side of a vertical centerline See that the oil drain line slopes downward its entire length, so that there is no place for the oil to collect inside of the oil line. Especially on new installations, the line should be closely checked and any "sink" traps eliminated, Make sure that the turbocharger drain is connected to some unrestricted place on the engine above the level of the oil in the crankcase. If the oil drain enters the crankcase below the oil level, it will cause the foamy oil to back up in the drain line and the bearing housing sump, thereby causing leakage . And finally check the drain lines. Those made form a rubber lined, fabric covered hose may not cause any problems at all after running several years in one location, even though the hose itself has become extremely brittle. When replacing the turbocharger though, it is possible that this type of drain line could be disturbed or bent, causing small pieces of the drain line to break off and partially obstruct the flow of oil. To prevent this from happening, a rubber, fabric type of drain line should always be replaced with a new line when replacing the turbocharger.

Engine Breathers:
Also, oil leaks in a turbocharger may be the result of the crankcase breather system. Either atmospheric or positive ventilation systems may not be large enough to handle the somewhat higher "blow by" which exists in turbocharged engines. It is recommended that the engines breather capacity be increased when a turbocharger is added. Even when the systems capacity is adequate, the elements in the systems breather will become partially clogged through use. Also, the breather may become clogged with mud or sludge in winter or under snowy and icy conditions. These conditions will cause positive pressure to build up in the crankcase. If this occurs, it will restrict the oil from flowing down the drain hose and into the crankcase, causing it to back up to the bearing housing.

Internal Crankcase Ventilation:
Some naturally aspirated engines have internal positive crankcase ventilation between the crankcase and the intake manifold. These vents must be plugged when a turbocharger is added, otherwise the crankcase will become supercharged and oil leakage will result. Another source of crankcase breather must be provided when these vents are plugged. Some engines have this extra breather, while others may not. In either case, make certain that the breather's capacity is adequate.