5 Common Factors for Turbo Oil Leakage-Part II

In one of our previous articles, we have already discussed 5 common factors for turbo oil leakage. As there are many causes for oil leakage, we’ll talk about another 5 common factors in this discussion, including incorrect oil supply, incorrect center housing clocking, overfilled oil, oil coking, and low-mounted turbo without proper oil scavenge pump installation.

Improper Oil Supply/Restrictor Mismatch
Supplying the right amount of oil to the turbocharger is essential for keeping its components in optimal condition. Too much oil can lead to leaks and create smoke from the exhaust.

Cause: The oil pump delivers too much oil because of excessive pressure, or an oil restrictor of the wrong size has been installed.

Effect: An elevated oil level in the cartridge can push oil past the seals, leading to leaks.

Symptoms: Blue smoke at idle and light throttle. Smoke appears immediately after installing a new turbo, with oil traces visible on both the compressor and turbine sides. This can be difficult to diagnose and is often mistaken for a defect in the turbo itself.

Solution: Match the supply pressure to the bearing type, such as using the correct sized oil restrictor, then set the oil supply pressure according to measurements taken when the engine is fully warmed and running at high RPM.

Incorrect Center Housing Clocking / Mount Angle
Always mount the turbo so that the oil inlet is on top and the oil return points downward.

Cause: The turbo’s center housing oil return port isn’t facing straight down, and with the installation angle off, the return flow ends up working against an uphill slope.

Effect: When oil builds up in the center housing, the pressure balance is disrupted, causing leaks through the piston rings at both the compressor and turbine ends.

Symptoms: Smoke is more likely to occur when the vehicle is tilted or driving uphill. The oil return line feels unusually hot, and upon inspection, oil buildup can be found in the center housing.

Solution: Rotate the turbocharger to ensure the oil return port points nearly straight down. A level can help with alignment, and be sure to account for the steep angles your vehicle may face in off-road or track conditions.

Excess Oil / Submerged Return Port
Engine oil is essential for reducing friction and ensuring proper lubrication of components; however, excessive oil levels can lead to oil aeration, crankcase pressure buildup, and subsequent smoke emission.

Cause: An excessively high oil level submerges the return port, preventing proper drainage

Effect: After lubricating the turbo bearings, the oil drains back to the oil pan by gravity. If the oil level is too high or the return line is blocked, drainage is restricted and exhaust smoke can occur.

Symptoms: On short cold runs, smoke can occur if the oil level in the oil pan exceeds the dipstick mark with telltale signs like oil seeping around the turbo’s return flange.

Solution: Correct oil level and relocate return above oil level.

Oil Heat Soak and the Risk of Coking in the Turbo Cartridge
When engine oil overheats and degrades, it leads to coking. These carbon deposits can wear down components and ultimately cause oil leakage.

Cause: Immediate shutdown after aggressive driving causes heat soak in the center housing, resulting in oil coking in the return line and piston ring grooves.

Effect: When resistance in the oil return line builds up, it gradually accelerates seal wear over time, resulting in more frequent blue smoke.

Symptoms: After the engine warms up, smoke intensifies. Inspection of the return line reveals coke deposits, and the front catalyst section is often contaminated with oil.

Solution: Make it a habit to cool down the vehicle with gentle cruising before shutting off. Always use the correct oil grade and change it on schedule. Make sure that the water-cooling system works properly and that heat insulation is in place.

Low-Mounted or Rear-Mount Turbo without Scavenge Pump
Ensure correct turbo positioning. When the turbocharger is installed in a low or rear-mounted configuration, an external oil scavenge pump is required to return oil effectively to the engine’s oil pan and prevent oil accumulation in the center housing.

Cause: Turbo sits below oil level.

Effect: When oil builds up inside the center housing, it can start leaking, especially during heat soak conditions.

Symptoms: Restarting the engine soon after shutdown can lead to smoke, especially in mid- or rear-mounted turbo setups. You’ll often notice oil stains along the return line—a clear sign of oil buildup and poor drainage.

Solution: A small catch tank at the turbo outlet, paired with a heat-resistant oil pump and a check valve, helps ensure smooth oil return. The pump should feed oil back into the oil pan, with all lines made from heat- and oil-resistant materials and properly secured to prevent vibration.