What is the best way to fix a turbocharger noise problem? Our guide details what might have damaged the turbo and what to do about it.
The exhaust gas turbocharger is used to increase the performance of internal combustion engines. The engine exhaust gases drive a turbine, and the rotation of the compressor wheel connected to the turbine means that more fresh air is simultaneously supplied to the engine. The technology has been further developed in recent years and is now standard for diesel and gasoline engines.
The advantage of turbochargers: The increase in output enables the use of smaller engines with less displacement – which naturally consume less fuel.
However, turbochargers are also controversial because the technology is expensive and can cause serious engine damage in the event of a problem.
There is no substitute for displacement,” is an old saying of the regulars. And yet, since the early 2000s, a lot of displacement has been replaced – without the performance falling by the wayside. And through the turbocharger. Keyword “downsizing”: less displacement and fewer cylinders mean less internal engine friction and thus less fuel consumption. In connection with the turbocharger and direct injection of the fuel, the emission and consumption values of the cars have been optimized without any loss of performance.
The manufacturers are now squeezing up to 270 hp from a small 1.6-liter four-cylinder gasoline engine (Peugeot RCZ-R). Not so long ago, car manufacturers were still using six or eight-cylinder engines for such performance spheres, with a displacement of four liters and more.
The days of large turbo holes are over. New technology and smaller chargers improve the responsiveness.
The turbocharger is also called an exhaust gas turbocharger, because it uses the energy of the exhaust gas to “charge” the engine with additional fresh air and thus increase its output. This is why turbo engines are also referred to as charged engines.
The turbocharger essentially consists of two turbines, the turbine wheel and the compressor wheel. Both are connected to one another via a shaft, but are installed in two separate housings. The turbine wheel sits in the engine’s exhaust tract on the exhaust manifold. The turbine is set in motion by the pressure of the hot exhaust gases. And very quickly, with up to 300,000 revolutions per minute. The compressor wheel, which is connected to the intake tract of the engine, rotates at the same speed at the other end of the shaft. The rotating compressor wheel sucks in additional fresh air, compresses it in the compressor housing and then presses it into the cylinder with overpressure.
In addition to the increased amount of fresh air, additional fuel can now be injected, which increases the performance of the engine. In addition, powerful turbo engines often have a charge air cooler. This has the task of dissipating part of the heat that is generated when the air is compressed. Since gases expand when the temperature rises or contract when the temperature falls, the cooling of the charge air enables a higher air throughput in the combustion chamber.
This in turn increases the efficiency and performance of the engine.In contrast to the turbo, engines without supercharging suck the fresh air into the cylinder solely through negative pressure. This is caused by the downward movement of the piston in one of the four working cycles of the engine, the so-called intake cycle. Therefore, engines without supercharging are also called naturally aspirated engines.
Boost pressure control
Regulation is required so that the boost pressure of the turbo does not reach a critical level when the engine speed increases. Otherwise the turbo and other engine components would be overloaded. Regulation usually takes place via a valve (wastegate valve) that is installed on the exhaust side of the turbocharger. When open, it guides the exhaust gases past the turbine wheel so that the turbine speed and, as a consequence, the boost pressure are reduced.
When and how far the valve opens is controlled by the vacuum unit. It essentially consists of a membrane and a spring and is connected to the fresh air side of the charger via a line. At a certain boost pressure, which acts against the diaphragm in the vacuum unit, the spring gives way and opens the wastegate valve in the turbo’s exhaust system via an interlocking.
More power through more boost pressure. In tuning, an increase in the maximum boost pressure is often sought in order to achieve a further increase in engine performance. To achieve this, the wastegate valve must only open at a higher pressure. This is achieved mechanically, for example, by increasing the spring preload. So-called steam wheels were also widespread until the 1990s. An additional valve reduced the pressure that reaches the vacuum unit. The name steam wheel is derived from the fact that the valve could be controlled mechanically from the interior of the car. In modern cars, the throughput is controlled by electromagnetic valves that can be programmed accordingly (chip tuning).
Variable turbine geometry (VTG)
More steam from hot air: Instead of a wastegate valve, turbochargers of diesel engines in particular have guide vanes that control the flow of exhaust gases to the exhaust gas turbine. Such turbochargers are known as VTG (variable turbine geometry) turbochargers. Like the wastegate valve, the guide vanes are controlled by an interlocking unit in the vacuum unit. If the guide vanes are closed, the exhaust gas flow passes the turbine.
In the low to medium speed range, the blades open only minimally, which promotes the flow to the turbine and the response behavior. Because the speed of the exhaust gas stream hitting the turbine is very high due to the small opening, the turbine blades are also flown against the outer edge, which creates a higher leverage effect. Finally, under full load, the blades open completely so that the maximum amount of exhaust gas can flow in. The turbocharger now reaches high speeds and thus high boost pressure.
Since VTG systems are sensitive to high temperatures, they were only used in diesel engines until a few years ago, where the exhaust gas temperature is significantly lower. In order to cope with the high temperatures of a gasoline engine, VTG systems require the use of expensive materials. Porsche was the first manufacturer to use VTG turbines in gasoline engines (911 Turbo and 718 Boxster / Cayman S). In the meantime, however, the technology has also reached mass production. The 1.5 TSI engine in the Golf 7 with 130 hp uses a VTG charger. More volume models are likely to follow soon.
Biturbo / twin turbo engines
Many supercharged engines now have two turbochargers. Such engines are called biturbo or twin-turbo engines. Instead of one large turbocharger, two smaller, identical turbochargers are used, which share the exhaust gas flow of the cylinders for the drive. In a V-six, each turbocharger uses the exhaust gases from a cylinder bank with three cylinders each. The advantage of two turbochargers is their lower mass inertia.
A large turbocharger requires more energy, and thus higher speeds, in order to get going and to build up usable boost pressure. Until then, the engine works like a naturally aspirated engine, i.e. with significantly less power, especially since part of the energy for driving the turbine guide vanes is “lost”. The phenomenon of lack of power up to a certain speed range is known as turbo lag and is typical of early turbo engines of the 80s and 90s.
Since this response is undesirable, engine developers use smaller turbochargers. This is because the exhaust gas brings the turbine wheels up to the required speed earlier to blow compressed air into the engine. Two turbochargers are used to deliver sufficiently compressed air even at high speeds. In rare cases, there are also four turbochargers, such as the Bugatti Veyron.
Sequential charging and register charging
Instead of two identical turbochargers, some engines have a small and a large turbocharger. To improve the response behavior at low speeds, only the small turbocharger works at the beginning, which responds with less delay, often just above idling speed. At a certain engine speed, when the exhaust gas flow is sufficient, the large turbocharger is also switched on. Both turbochargers are now working at the same time. One speaks here of sequential charging, or sequential biturbo. In contrast to sequential charging, some engines have register charging.
The difference to the sequential biturbo lies in the alternating use of the small and the large turbo: At low speeds, only the small turbo charger runs here, which can be revved up faster. At higher speeds, the large turbocharger is “activated” via the switchover flap, while the small turbocharger then fails. Thus, the two turbochargers never run at the same time, but only alternately, depending on the speed.
How to fix a turbocharger noise problem: sometimes cleaning the turbocharger helps
Regular wear and tear is rarely responsible for a defect in the turbocharger. In many cases, turbocharger damage is due to an insufficient oil supply. The bearing surfaces of the connecting shaft between the turbine wheel and the compressor wheel are permanently lubricated with oil by an integrated circuit. If the oil supply to the turbocharger is impaired, scoring quickly forms on the bearing surface of the shaft. As a result, if you do not fix a turbocharger noise problem like this, the shaft can tear.
Reasons for insufficient oil supply: bad oil, foreign bodies or fuel in the oil, a clogged oil filter and also clogged oil channels in the engine. Turning off a hot turbo engine should also be avoided at all costs. After a long drive at full load, the exhaust side of the turbo becomes extremely hot (up to 1000 ° Celsius). After the engine has been switched off, the oil and cooling water supplies to the turbocharger are also interrupted. The heat is no longer dissipated and the “standing” oil can burn to carbon, which clogs the oil ducts and then affects the oil supply.
Burning oil in the engine is also critical. The resulting oil carbon can block lines or settle on the turbine. This leads to thermal problems, an imbalance of the turbine and thus to the sluggishness of the turbo. Such dirty turbochargers can possibly be cleaned with special sprays. In the optimal case, even without dismantling the turbo – the most economical form of turbo charger repair possible. Such a turbo charger cleaning set is supposed to loosen dirt like coal, rubber and paint from the turbines without damaging the catalyst , as an early step to fix a turbocharger noise problem.
Fix a turbocharger noise problem: damage from soot particle filter
The turbine wheel is firmly connected to the shaft. The compressor wheel is screwed on. If the shaft gets hit, the repairer can help.Problems with the exhaust system are also a common cause of damage to the turbocharger. Diesel engines with soot particle filters are particularly susceptible. If the particle filter clogs, for example when the car is mainly used in city traffic, where the filter cannot burn out, there is a backwater in the exhaust tract, which acts directly on the turbine.
The forces acting on the turbine wheel can be so strong that the shaft receives a blow. As a result, a typical symptom occurs: the whistling of the turbocharger. The unusual noise heralds a damaged turbocharger shaft. The whistling can also occur in the initial stages of a lack of oil supply.
If you notice such whistling noises on your turbo engine, you should take the car to a workshop as soon as possible and have it examined to prevent serious damage. Any mechanical damage to the exhaust system that reduces the exhaust gas flow has the same dangerous effect. For example, an exhaust pipe that has been pushed shut by a parking bump. Such harmless-looking damage must be repaired immediately in turbo engines.
Fix a turbocharger noise problem: Foreign object damage
Another known cause of damage to the turbocharger is foreign objects that get into the intake system. Due to the enormous speed of rotation, even the smallest particles can cause damage. In vehicles with a high mileage, the compressor wheels have been polished smoothly over the years. In the best case scenario, only the engine power is reduced because the compressor wheel shovels less air into the engine.
Damaged or broken blades on the compressor wheel cause an imbalance, which can result in a blow to the shaft or its bearings, which often results in a leak in the oil circuit. In the final stage, the rotating wheels grind in the housing and the turbo dismantles itself. Damaged compressor wheels can be diagnosed relatively easily, since the compressor wheel can be examined carefully after dismantling the supply air line.
It is more complicated on the exhaust side, where the turbine wheel is only visible after the turbocharger has been completely dismantled. In this case, however, it is usually not foreign bodies that damage the turbine wheel, but engine parts that are triggered, such as the exhaust manifold.
Engine damage from a toothed belt break is also a source of danger. If the repair does not remove all of the metal particles that have come loose from damaged valves or pistons, major damage can occur immediately when the engine is started up, which paralyzes the engine again.
Fix a turbocharger noise problem: Symptoms of turbocharger damage
|Turbocharger whistling||If the turbocharger whistles with increasing speed, the shaft is damaged or knocked out. The whistling sound is caused by the metallic friction.||Overhaul / repair turbocharger|
|Bluish smoke||Indicates an oil leak in the turbocharger, for example due to a knocked out charger shaft. The oil used to store and cool the shaft gets into the exhaust and burns.||Overhaul / repair turbocharger|
|Increased oil consumption||Turbocharger bearing damage, defective or clogged oil supply lines.||Check the turbocharger oil lines and replace if necessary|
|Black smoke||Can be caused by insufficient air supply. During combustion, there is a disproportion in favor of the fuel content, black smoke is produced. A leak in the fresh air line could be the cause.||Check the hoses and connections of the suction or compressed air lines for leaks and replace if necessary. Low-lying lines (charge air cooler) can loosen / damage if they hit the ground.|
|Loss of power I||If there is a permanent lack of power, the compressor wheel can be damaged. Broken blades no longer push enough air into the cylinders.||New compressor wheel, overhaul turbocharger, protect intake tract from future foreign matter.|
|Loss of power II||If the VTG unit is covered in soot, the guide vanes will jam. The charger can only build up pressure late or no longer at all.||Dismantle and clean the loader, eliminate the cause of the increased soot formation.|
|Too high boost pressure||The valve for boost pressure regulation, control lines or vacuum unit is defective.||Replace vacuum unit, make valve free to move, repair control line.|
|Noises from the turbocharger||Exhaust system back pressure too high, compressor wheel or turbine wheel damaged, leak in front of the turbine (for example on the manifold).||Check exhaust for damage, repair compressor or turbine, eliminate leak.|
Defects also occur in the area of the vacuum unit and the wastegate valve. For example, the solenoid valve, the membrane of the vacuum unit or the hose system between the components can be defective or leaky. This also applies to the linkage of the vacuum unit, which opens the wastegate valve or, in the case of VTG chargers, controls the angle of the guide vanes. Because the mechanics can lose their freedom of movement over time.
Whether it is a loss of power, whistling noises, increasing oil consumption or smoke development – the engine should be examined in a specialist workshop as soon as symptoms of turbocharger damage are detected. The spectrum of sources of error is wide. And the causes are difficult to verify for the layman. Since much damage occurs gradually, a visit to the workshop in good time can save a lot of money.
Once the turbocharger has been completely dismantled, broken parts can also damage the engine itself. On the other hand, severe oil loss can destroy the expensive catalytic converter. In many cases it is worth overhauling or repairing the turbo. However, not all workshops dare to do this work. Because repairs require experience and special tools. For example, all rotating parts must be finely balanced before installation. Even authorized workshops prefer to completely replace the turbocharger unit.
Repair costs of several thousand dollars are the result, because the new turbocharger alone usually costs over $1,000. A repair to fix a turbocharger noise problem is cheaper. At prices between $200 and $600, the damaged parts are replaced and the loader is re-sealed. In addition to the repair costs, there are also the costs for removing and installing the turbocharger.
The dismantling of the turbocharger can be done in a workshop. After the expansion, the turbo is sent to the specialist. He examines the damage pattern, consults the workshop to rectify the cause and repairs the turbo. Many repairers keep the most common turbochargers in stock and deliver reconditioned chargers with a warranty of up to two years in exchange for the old part. The prices for refurbished turbos start at less than 300 euros, often less than half of the new price. However, it is important that all causes of damage in the periphery of the turbocharger have been eliminated so that damage does not occur again.
Gerhardt Richter is a writer and a trainer at trade technical colleges, specializing in carpentry, plumbing, mechanics and construction.