ASK THE MECHANIC. My turbo leaks oil into the engine bay

Thursday November 29 2018



Mercedes ML 320 CDi

Mercedes ML 320 CDi 

By Paul Kaganzi

Hello Paul, I drive a 2007 diesel Mercedes ML 320 CDi. Lately, I have noticed that the turbo leaks oil into the engine bay. Does this mean the turbo is faulty and needs replacement? The car accelerates very well and I feel the turbo effect when I kick down. Mugabi

Hello Mugabi, the turbo charger may not need replacement, especially if its performance is still good. However, a mechanic may need to inspect the quality of engine oil, condition of the turbo oil seals and air intake system restriction (dirty air cleaner) as well as a faulty crank case ventilation system which can cause oil leaks in the turbo charger. A turbo charger requires good engine oil for lubrication, cooling and performance enhancement as its fast moving components tend to heat up and may suffer frictional wear if not well lubricated. The turbo charger design allows it to utilise the engine oil which flows into the turbo housing and is drained out through designated ports.
The turbo charger is designed with different seals which help to prevent high pressure gases and leakage of oil into the centre turbo housing and air intake system. These seals are protected by engine oil and may wear out if you delay to renew the engine oil or service with the wrong type of engine oil. Aged or poor quality engine oil can develop thick sludge which builds pressure and causes damage to the seals. Consider replacing the two red oil seals at the air intake points, these should be inspected during service B and other service routines for leakages.
Accumulation of dirt in the air cleaner elements can cause a pressure drop in the air intake tunnel, which leads to a build-up of vacuum at the turbo compressor inlet. This vacuum will have a suction effect which will draw oil from the bearing housing to the compressor housing and onto the induction system. Maintain the air cleaner elements or replace them on time. Ensure that all turbo oil drain points are pointing downwards for gravitational drain and are not kinked or restricted. A clogged crank case ventilation system will lead to a build-up of pressure in the crankcase which in turn prevents oil from draining out of the turbo into the engine sump.
This leads to a build-up of oil in the turbo bearing housing which will leak past the metallic ring like turbo seals. Most of the issues around the turbo charger performance will start with the choice of engine oil and maintenance of its quality.

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