Like any mechanical component, turbos are vulnerable to wear and tear as the miles add up. They are most vulnerable to lubrication-related issues (e.g., poor quality oil, not changing the oil often enough, dirty oil, low oil level or low oil pressure), but turbos can suffer other complications as well. High exhaust temperatures may cause the turbine housing to crack and leak. Poor air filtration that allows dirt and dust to be sucked past the air filter can erode the compressor wheel over time, causing a gradual loss of turbo efficiency and boost pressure.
Turbos use different types of bearings, including steel and ceramic ball bearings, full floating bronze bearings that ride on an oil film and rigid bronze bushings. They all depend on a constant oil film to minimize friction and wear. If the bearings or bushings become worn, the shaft may wobble as it rotates. This creates harmonic vibrations that can prevent the turbo from achieving its normal operating speed and boost pressure. A buildup of deposits on the shaft or bearings will create drag that can also prevent the turbo from spinning freely. If the shaft binds up, the turbo may not spin at all.
A turbo may also fail to deliver normal boost pressure if there are leaks in the intake plumbing. Noise, such as whistles or hisses, would indicate air leaks in the turbo housing, connections or hoses.
The classic symptoms of turbo trouble include:
Loss of power: Power and torque will be noticeably less because the turbo isn’t spinning as fast as it should and is not developing normal boost pressure. This can be caused by worn or damaged shaft bearings, airflow obstructions in the intake or exhaust systems, air leaks in the turbo discharge and intercooler plumbing, dirt or debris clogging the intercooler, or a leaky wastegate or defective wastegate electronic controls. Low boost pressure can also be caused by erosion wear on the compressor or turbine wheels. The tolerances inside the housings are very close, so any increase in the clearances can reduce boost.
Excessive oil consumption and/or blue smoke in the exhaust: If you discover oil inside the compressor housing, the seal on the compressor side of the center housing is leaking.
Reduced throttle response in an application with a variable nozzle or variable vane turbo: Carbon can build up on the vanes, preventing them from changing position. The vanes may become stuck in the low RPM or high RPM position. Using an aerosol cleaner designed for this purpose (or for cleaning EGR valves) can often loosen and remove the carbon deposits inside the turbine housing.
Sluggish throttle response and/or loss of power due to carbon deposit buildup on the turbine wheel: Deposits add mass and inertia, which make it harder for the turbo to spool up quickly. Use an aerosol cleaner to loosen and remove the deposits.
Sluggish acceleration and/or loss of power due to a damaged or eroded compressor wheel or turbine wheel:If the blades are worn down, broken, bent, cracked or damaged, the turbo may not deliver normal boost pressure. Replace the damaged parts or the turbo.
Intake and exhaust manifold gasket leaks caused by excessive boost pressure, heat or corrosion: Intake plumbing leaks typically produce whistling noises when the engine is under load. Exhaust leaks will produce a familiar growl, hiss or rumble.
A short test drive will usually make it obvious whether or not a turbo is delivering normal boost pressure and power. Most vehicles have a boost gauge, so if the gauge shows no needle movement, very slow response or failure to achieve normal boost levels, there is likely a problem with the turbo or its controls.
If the Check Engine Light is on, use a scan tool to check for trouble codes. Codes that indicate turbo troubles include P0033 (bypass valve control circuit), P0034 (bypass control valve circuit low), P0035 (bypass control valve circuit high), P0234 (overboost condition), and P0235 to P0250 (various control faults). A scan tool can also be used to check the PID status of the wastegate on many applications and to check the operation of the wastegate valve.
To inspect the turbo, remove the turbo air inlet duct plumbing and peer inside with a bright light. If the compressor wheel is damaged (broken, chipped or missing blades), the turbo needs to be replaced. The intercooler and rest of the inlet plumbing also need to be inspected and cleaned to remove any debris that might enter the engine and cause damage.
The turbo compressor wheel should spin freely. If it binds or turns roughly, the bearings are probably worn or damaged and the turbo needs to be rebuilt or replaced. The presence of oil on the compressor wheel indicates a leaky shaft seal on the compressor side. Oil on the exhaust turbine wheel (or blue smoke in the exhaust) would indicate a leak shaft oil seal on the turbine side of the center housing.
If a turbo has damaged shaft bearings, the center “cartridge” can usually be replaced separately from the compressor and turbine housings. A remanufactured cartridge includes the center housing, shaft, bearings or bushings, seals, turbine wheel and compressor wheel preassembled and ready to install. Replacing a cartridge is less expensive than replacing the entire turbo, but it also requires more disassembly and assembly labor.
If the turbine or compressor housing is cracked, worn or damaged, that may have to be replaced as well; or, you could simply replace the entire turbo assembly with a new or remanufactured unit. Most new and remanufactured turbos come with new heat shields (which are often corroded and in poor condition on high-mileage turbos), a new wastegate (if it is part of the turbo) and a warranty.
If a new wastegate is not included with a replacement turbo, this should also be changed on high-mileage vehicles. The same goes for the boost controller on variable nozzle and variable vane turbos. Additional parts you may also need include hoses, clamps, motor oil and a filter. ■