Turbochargers are essentially compressors that direct more air into the engine’s cylinders in order to produce additional power. A turbo derives its energy source from both temp and pressure of exhaust gas. Intake air enters through the air cleaner into the turbo compressor inlet. The air is compressed which raises air density and volume.
If the engine is equipped with an intercooler, the compressed air passes through the intercooler before it enters the engine, to cool and further increase air density. The increase of dense air enters the fixed volume of the combustion chambers. The increase of the rate of airflow allows a higher fuel flow rate.
Once the air/fuel charge is burned, the charge exits on the exhaust stroke into the exhaust manifold. The high-temperature exhaust gas then enters the turbocharger’s turbine that in turn drives the turbo compressor, charging the intake air, continuing in a cycle that forces high density air into the engine, mixing with the correct amount of fuel to maintain a proper air/fuel ratio, producing more power.
Typical operating speed of a small turbo can be as high as 240,000 rpm. Keeping that in perspective, it becomes obvious that maintenance and proper installation procedures are critical to keeping a turbo alive and well.
Turbo systems typically feature a compressor bypass valve (commonly referred to as a blow-off valve) on the intake side and a wastegate in the exhaust flow side. The blow-off valve is a pressure relief device on the intake path to prevent the turbo’s compressor from going into surge. The blow-off valve should be located between the compressor discharge and the throttle body, downstream of the charge air cooler.
When the throttle body closes rapidly, the airflow is quickly reduced, causing airflow instability and pressure fluctuations, which lead to a surge. Surge can eventually lead to thrust bearing failure due to high loads. The blow-off valve uses a combination of manifold pressure and spring force to detect when the throttle is closed. When the throttle is closed rapidly, the valve vents boost in the intake stream to relieve pressure.
Lack of proper maintenance is probably the leading cause of turbo failures. Journal and bearing failures are frequently caused by a lack of lubrication. Upon examination, the shaft journals will show discoloration as a result of excessive heat. Lack of lubrication may reveal a bluish discoloration.
Bearing or journal failures can be caused by the use of oil viscosity that is too heavy for the application, or lack of lubrication resulting from a failed or blocked oil supply line.
Also, even a tiny spec of dirt in an oil orifice can reduce oil delivery to the point of turbo damage. Dirt/grit/sludge in the oil can easily damage journals and bearings.
Using the correct type and viscosity engine oil and following regularly scheduled oil and filter changes is of paramount importance to protect the extremely close tolerance turbocharger assembly.
A turbocharger’s compressor impeller spins at extreme speeds and can quickly be damaged by any foreign particle that enters the inlet stream. Keeping the air inlet path clean is vital, which means paying close attention to air inlet cleanliness and regular inspection and replacement of the air filter.
Exhaust gasses/pressure enter the turbo. If any debris exists in the exhaust stream, such as dirt, rust scale, a piece of broken piston rings, etc., the debris hits the turbine blades with enough force to chip away at the blades.
Eventually, one or more blades can break off, immediately creating an imbalance and subsequent bearing failure.
Change the oil
The oil supply to the turbocharger experiences an enormous amount of heat. Turbos also operate at incredible speeds, up to as much as 200,000 rpm and at temperatures as high as 1,922 degrees Fahrenheit.
As you might imagine, correct oil delivery and pressure are critical to turbocharger life. Oil delivered to the turbo is responsible for lubricating thrust and journal bearings, stabilizing the rotating shaft and journal bearings and serving to cool the turbo by helping to dissipate heat.
Many consumers are under the assumption that operating the engine with dirty or contaminated oil isn’t an issue, since the engine’s oil filter will capture any particles before they can enter the oil circuit.
Wrong. Even the smallest particles can wreak havoc in the high-speed turbocharger by blocking off internal oil passages. Starving a turbocharger of oil, even momentarily, can result in a quick death to the unit.
A turbocharged engine (gas or diesel) requires more frequent engine oil changes. A full-synthetic oil is generally considered the best choice.
With regard to a production street vehicle that is factory turbo equipped, it’s best to use the type of oil recommended by the vehicle maker.
Properly lubricating the turbo is key to long turbo life. If supplied with clean oil and prevented from ingesting debris, a turbo should last as long as the engine. When a turbo fails, it’s generally not the fault of the turbo, but a fault that affects the turbo.
Don’t ignore the intake air filters. Tiny particles that enter the turbo can result in turbine wear. Air filter inspection and replacement intervals are more crucial for a turbo-equipped engine.
Following a hot shutdown, heat soak begins. Heat in head, exhaust manifold and turbo housing soaks into the turbo center housing, raising temperature that can result in oil coking. Some turbos feature water-cooled center housing, which uses engine coolant to act as heat sink. Water lines use a thermal siphon effect to reduce heat.
Located on the exhaust side of the turbo, a wastegate controls boost pressure. Note that some commercial diesel applications don’t us a wastegate, featuring a “free floating” turbocharger.
For gasoline engines, there are two types of wastegates: internal and external. Each type allows bypass of exhaust flow from the turbine wheel to limit boost pressure to the design level.
Internal wastegates are built into the turbine housing, featuring a flapper valve, pneumatic actuator, crank arm and rod end.
An external wastegate is located on the exhaust manifold. The advantage of an external wastegate is that the bypassed exhaust flow can be reintroduced into the exhaust stream further downstream of the turbine, which tends to improve turbine performance.
Wastegates are featured in many systems in order to control boost to prevent over-boosting. However, some newer designs such as VGT turbochargers or Garret’s VNT (variable nozzle turbine) found in some production vehicles feature variable vane designs that eliminate the need for a separate wastegate.
Any restrictions in the oil drain line will cause the oil to back up inside the turbocharger and be forced past the seals. The seals located at the compressor and turbine ends of the turbocharger keep pressurized air/exhaust gasses from entering the turbocharger and then into the crankcase. They also control oil from entering the compressors.
Oil leakage from the turbocharger seals can be caused by excess crankcase pressure due to poor crankcase ventilation such as a plugged PCV system or an open port from the intake manifold to the crankcase. Oil leaks past the seals can also be caused by excessive engine blow-by due to worn piston rings, valves, etc. Air filter restrictions can contribute to excessive vacuum on the compressor end seal, causing oil to be drawn past the seals.
Some turbochargers feature water cooling, which aids in heat transfer and reduction of oil coking, especially after the engine shuts down. A water-cooled turbo should be mounted below the upper-most water level in the cooling system in order to provide thermal siphoning and flow of coolant through the turbocharger’s bearing housing.
If the engine has experienced any issues, such as low oil pressure, low oil volume, sludge buildup, excessive crankcase blow-by, piston ring failure, scored main or rod bearings, mechanical failures that have resulted in metal particles dispersed into the engine, etc., it is highly likely that the turbocharger has been affected. If engine issues have been discovered, do not ignore the turbocharger.
Don’t treat the turbo as a “separate accessory.” Any issue dealing with lubrication (lack of oil or contamination) directly affects the condition of the turbo.
Safety note: If performing an on-vehicle inspection of the turbocharger, never place your fingers near the turbo compressor inlet if the engine is running.
Never place anything into or close to the compressor with the engine running. The blades of the compressor will act like a wood chipper and will try to eat anything in its path resulting in either severe injury and/or destruction of the compressor blades.
With the engine off, remove the compressor’s air inlet and inspect the compressor for blade damage. Any deformation, chipping or blade edge erosion is cause for compressor replacement.
Rotate the shaft by hand and feel for any sensation of binding or drag. Push the shaft to one side (applying lateral pressure) and rotate. Any difference in rotating feel (easy to rotate with no lateral pressure but drags when pushed to one side) is a sign that the turbo needs to be rebuilt or replaced.
Axial play in the shaft should be in the range of 0.001 – 0.004 in., which would require a dial indicator for checking. However, if you can noticeable feel axial play (in/out) by hand, the thrust bearing is worn, again requiring rebuild or replacement.
Also — and this cannot be over-emphasized — when replacing a turbocharger, never allow a dry start. Always make sure that the turbocharger is pre-oiled prior to starting the engine. A dry start can kill a turbo in very short order. When a turbocharger has been replaced, crank the engine for 10-15 seconds or until stable oil pressure is achieved, with the fuel and ignition disabled. Once the engine is started, allow it to idle for about five minutes while checking for leaks.
Late model diesel engines equipped with turbochargers present additional potential issues. Light trucks produced beginning in 2007 feature DPF (diesel particulate filter). If the filter becomes plugged or restricted, exhaust gas temperatures will increase, excessive carbon buildup will occur, along with increased exhaust back pressure. This can in turn result in turbocharger failure as the turbo tries to work overtime to compensate.
Turbo diagnosis tips
(The following provided courtesy SMP Corp.)
Vehicle manufacturers are adding turbochargers at a double-digit rate. Over the next five years, the turbo market is expected to grow to more than eight million turbocharged vehicles. As the number of turbocharged vehicles increases, more technicians will see vehicles with turbocharger issues in their shops. But there’s already confusion in the field.
To help technicians diagnose turbocharger repairs, here are a few important diagnostic and repair tips to keep in mind. As a note up-front, most turbocharger diagnoses (aside from noise and low power issues) require scan data and an understanding of operation at the technician level.
What causes a turbocharger to malfunction?
Before we start, let’s highlight what causes a turbocharger to malfunction in the first place. Symptoms of a malfunctioning turbocharger include loss of power, excess smoke, high fuel consumption, overheating, high exhaust temperature, and oil leaks from the turbocharger. But it’s important to note that defects in other components can produce the same symptoms.
Before wrongly attributing the issues to the turbocharger, remember that turbocharger performance can only be impaired by mechanical damage or blockage caused by debris.
Signs of a damaged turbocharger
If you hear whistling noises coming from the turbocharger, it’s likely due to an air/gas leakage caused by pre-turbine exhaust gas or air/boost leaks. Your first course of action should be checking all of the joints. If the noise continues, check the turbo clearances and wheels for housing contact.
If the turbocharger rotor assembly has seized up or is difficult to rotate, the problem is likely tied to the degradation of the lubricating oil. When the oil degrades, it can lead to carbon buildup in the bearing housing interior. The carbon buildup will ultimately restrict rotation.
Two other issues that can cause the rotor to seize up include insufficient or intermittent drop-in oil pressure and dirt in the lubricating oil.
Another important detail to keep in mind is that a turbocharger has specific axial and radial rotor clearances. Sometimes, the clearances can be misdiagnosed as worn bearings.
In reality, clearances that are out of specification may be associated with a lubricating oil issue. Check for insufficient oil, or oil contaminated with dirt or coolant.
To determine if the turbocharger has been damaged by foreign material, inspect the turbine wheel or impeller. You will clearly see any foreign material that has entered through the turbine or compressor housings. If the blades are damaged, the turbo is already destroyed. Look for metal that has come off the turbo in the intake tubes. Metal particles in this area may indicate a damaged engine.
Common trouble codes
DTC: P0299 (Underboost)
Potential issue: Wastegate stuck in open position or leak between compressor and throttle.
DTC: P0234 (Overboost)
Potential issue: Wastegate stuck in closed position, wastegate vent solenoid stuck in vent position, or leaking or disconnected control hose.
(Courtesy of BorgWarner)
Probable cause: Dirty air filter system
Type of failure: Low power/insufficient boost; black smoke; blue smoke; high oil consumption; oil leak at compressor.
Probable cause: Suction and pressure line distorted or leaking
Type of failure: Low power, low boost; black smoke; turbo generates acoustic noise.
Probable cause: Excessive flow resistance in the exhaust system or leakage upstream of the turbo
Type of failure: Low power, low boost pressure; black or blue smoke; acoustic noise; high oil consumption; turbo compressor oil leak.
Probable cause: Oil feed and drain lines clogged or leaking
Type of failure: Blue smoke; high oil consumption; compressor oil leak; turbine oil leak
Probable cause: The crankcase ventilation is clogged
Type of failure: Blue smoke; high oil consumption; compressor oil leak; turbine oil leak
Probable cause: Coke and sludge in turbo center housing
Type of failure: Blue smoke; high oil consumption; compressor/turbine oil leak
Probable cause: Fuel system feed defective or misadjusted
Type of failure: Low power, low boost; boost pressure too high; black smoke
Probable cause: Valve guide, piston rings worn cylinder liners worn/excessive blow-by
Type of failure: Poor power, low boost; black or blue smoke; high oil consumption; compressor/turbine oil leak
Probable cause: Dirty compressor or charge air cooler
Type of failure: Low power, low boost; black or blue smoke; turbo acoustic noise; high oil consumption; compressor oil leak
Probable cause: Boost pressure control swing valve/poppet valve does not close
Type of failure: Poor power/low boost pressure; black smoke
Probable cause: Boost pressure control swing valve/poppet valve does not open
Type of failure: Boost pressure too high
Probable cause: Pipe assembly to swing valve/poppet valve defective
Type of failure: Poor power/boost pressure low; boost pressure too high
Probable cause: A defective piston ring sealing
Type of failure: Blue smoke; high oil consumption; compressor/turbine oil leak
Probable cause: Turbo bearing damage
Type of failure: Defective compressor/turbine wheel; low power, low boost pressure; black or blue smoke; turbo acoustic noise; compressor and/or turbine oil leak
Probable cause: Foreign body damage on compressor or turbine
Type of failure: Defective compressor/turbine wheel; low power, low boost; black smoke; turbo acoustic noise
Probable cause: Exhaust gas leaks between turbine outlet and exhaust pipe
Type of failure: Turbo acoustic noise
Probable cause: Engine air collector cracked, missing or loose gaskets
Type of failure: Low power, low boost pressure; black smoke; turbo acoustic noise
Probable cause: Turbine housing/flap damaged
Type of failure: Low power/low boost pressure; compressor/turbine wheel defective; black smoke; turbo acoustic noise
Probable cause: Insufficient oil supply to turbocharger
Type of failure: Defective compressor/turbine wheel; poor power/low boost pressure; black smoke; turbo acoustic noise
NOTE: Gas and diesel engine turbo systems usually feature a “swirl flap” located in the intake manifold to improve mixing of the air/fuel mixture. The swirl flap allows air movement to adapt to the engine load and speed. Depending on the specific design, the flap may be operated electrically or pneumatically. These flaps should be checked for smooth operation and for looseness. They are prone to coking in diesel systems.
New or reman
Turbochargers, depending on make/model/year, may be available new or remanufactured. Naturally, a reman unit (generally requiring a core return) will be less expensive, saving the customer some cash. Some of the firms that offer new or remanufactured units include: