Leaking turbocharger seals. Oil in exhaust. Oil in intake
Remove intake tubes and wash out oil. Re-install and run engine for short period. Remove intake tube and see whether oil is traveling from turbo to cylinder or visa versa. Oil in the exhaust system upstream of the turbocharger indicates malfunction such as problems with rings, pistons, or valves. If engine idles too slow, turbo does not turn allowing oil to leak from compressor seal. Leak in compressor seal can be caused by:

(a) air cleaner element clogged or restriction in duct between air cleaner and turbocharger which can cause oil to be drawn past the turbocharger seal at the compressor end,
(b) restriction or faulty check valve in turbocharger oil drain line, which may raise the oil level in the turbocharger center housing and cause seal leakage,
(c) malfunction in oil scavenge pump,
(d) restriction in engine crankcase breather,
(e) worn or damaged compressor wheel,
(f) turbocharger shaft bearings or bearing bores worn,
(g) crankcase pressurization causing backpressure into oil drain line due to piston blowby.

Another cause of turbocharger failures is inlet restrictions from plugged air cleaners, collapsing hose connections or undersized air pipes. These restrictions reduce the air supply to the turbo and ultimately to the engine resulting in excessive exhaust temperatures leading to turbine housing cracking and scaling or even turbine wheel failures.

Inlet restrictions also can produce a vacuum inside the compressor. This can cause over speed conditions in the turbo which can lead to premature bearing failure or even make a compressor wheel burst. This vacuum inside the compressor also can cause oil leakage into the compressor.

The turbo's oil seals depend upon a positive air pressure inside the compressor and turbine to "push" the oil inside the bearing housing and keep oil from seeping into the outer housings. In an inlet restriction situation, the vacuum wants to "pull" the oil past the oil seals. Prolonged oil leakage into the compressor can lead to oil seal damage and excessive engine smoking.

Prolonged engine idling also can cause turbocharger oil seal failure, this time on the turbine side. Continued idling causes the turbo to rotate without producing boost. Consequently, a vacuum condition on the turbine side tries to "pull" oil past the turbine-side oil seal and into the turbine housing.

If exhaust is smoky

Check compressor outlet for oil, check compressor inlet for oil.

If compressor outlet is not oily, check turbine outlet for oil.

If oil is present, Turbo is OK, check PCV system for clogs.

If oil is found, it is an internal engine issue. If it is not found in turbine, Turbo is OK, smoke is from car engine.

If compressor inlet is not oily, check for restriction in turbo oil supply tube.

Repair restriction if found. If none is found, check for restriction in the turbo oil return tube. Remove restriction if found, if now, replace turbocharger.