Sluggish Engine? Turbo Failure?


Most cars that are fitted with turbos these days do not need them. Indeed, most non-turbo models comfortably outperform their counterparts on all levels, by employing different but vastly more reliable technologies.

Nevertheless, automakers have latched onto turbos as a selling gimmick, fitting them to ridiculously small capacity engines, making the load on both engine and turbo impossibly high and drastically reducing the useful life of both. Manufacturers will claim that they have perfected the design of their turbos, but the truth is that turbos are manufactured by outside manufacturers, not the manufacturer of your favorite model of car.

All things considered, turbos are not as good or useful as they are made out to be, but if you have a new turbo fitted car, here are some pointers on what can go wrong and what to do when it does.

The Symptoms of Turbo Failure Include:

  • Excessive oil consumption: Oil consumption increases dramatically as oil escapes past damaged seals and bearings.
  • Excessive smoke emission from the tailpipe: Oil escaping past damaged bearings and seals enter the engine via the inlet tract and is burned along with the air/fuel mixture, resulting in excessive smoke emissions.
  • General loss of power or sluggishness of the engine: At high engine RPMs, this is caused by the turbine wheels not rotating rapidly enough because of sticking or binding due to damage to the turbo shaft. This could also be caused by the wastegate getting stuck in the partially open position, resulting in the incorrect volume of air being delivered to the engine.
  • Increased fuel consumption: Loss of pressure in the inlet tract may induce a driver to use larger throttle openings to maintain speed and power delivery, resulting in poor MPG but doing nothing to improve power delivery.
  • High pitched whistling or screeching sounds as the engine RPM increases: This is caused either by the high-frequency vibration of the turbine wheels due to damage to the turbo shaft, indicating imminent destruction of the turbo, or by compressed air escaping through small ruptures or leaks in the inlet tract.
  • Illuminated CHECK ENGINE light or BOOST CONTROL light: On turbos with electronic boost control, this could indicate a variety of possible causes, ranging from over/under boosting, to the complete failure of the turbo. This issue should only be investigated by trained personnel, as the turbo could later be affected by misguided attempts to fix or identify the cause of the malfunction.

How Does a Turbo Work?

The turbo is designed to and meant for the purpose of delivering compressed air to the engine in order to increase the gas/air mixture volume, thereby obtaining better performance and engine power delivery.

The turbo is comprised of two gas turbines (separated from one another), one of which is connected to the outlet manifold and driven by the high-velocity exhaust gases. This wheel drives another turbine wheel by means of small diameter shafts that pass through the turbo casing, borne on two roller bearings, which are lubricated by pressurized motor oil. Enclosing the bearings are two oil seals that prevent pressurized motor oil from entering either the inlet tract or the exhaust system. This oil is returned to the engine via a return pipe connected to the bottom of the turbo on one end and the oil pan on the other.

The second turbine wheel, driven by the one on the exhaust side, acts as a centrifugal air pump. Due to its very high rotational velocity (up to 250 000 RPM), it compresses the atmospheric air that enters through the air filter to very high pressures. Depending on the turbine wheel diameter and configuration, pressures of 14-16 pounds per square inch are the norm rather than the exception.

In order to control the high volume of compressed air, use is made of a wastegate that dumps into the exhaust system the compressed air the engine does not need or cannot consume. This mechanism is sometimes controlled by the pressure in the inlet tract but in some cases, it is controlled by the engine management system. If fitted, the purpose of the intercooler is to cool down the compressed air that has become extremely hot by contact with the turbo casing and, to a lesser degree, by being compressed. Since more cool than hot air can fit into any given volume, thereby increasing power delivery, even more, intercoolers are generally fitted to high performance, large capacity engines. Intercoolers are heat exchangers and cool down the hot air that passes through them using the same principle as radiators that cool down hot water.

However, due to their design, the turbine wheels depend on high-velocity exhaust gases to function. For this reason, a turbocharger does not function at low RPMs; instead, it acts as a “choke” in the inlet tract until sufficient rotational velocity has been attained to compress the inlet air. This “choking” effect is known as “turbo lag” and is normal, albeit irritating and sometimes inconvenient. Most turbos only overcome turbo lag at engine RPMs of around 2300 and above. Modern designs have significantly reduced this effect, but it can be eliminated only by using smaller turbos to feed the main unit(s), a technique most recently employed by a German sports car manufacturer.

The main components of the turbo are:

  • Turbocharger
  • Air filter
  • Intercooler, if fitted
  • Wastegate (also known as a dump valve)
  • Actuator to operate the wastegate
  • Large diameter hoses or ducting to deliver compressed air to the engine inlet tract
  • Inlet manifold or inlet tract
  • Connections for lubricating oil and, if fitted, a connection for coolant

There are very few reasons that turbochargers fail. If you suspect that yours has failed or is in the process of doing so, ensure that the dealer you consult is knowledgeable about turbos. The symptoms of a failed turbo very often mimic those of other, unrelated issues and malfunctions, so expertise is important.

Here are some potential causes of turbo failure:

The use of incorrect or unsuitable grades of motor oil. A turbo operates under extreme conditions and demands the best lubrication it can get, which is always the make and grade recommended by the manufacturer. Dealers have been known to substitute cheaper or incorrect grades of motor oil to save costs at the time of a new car’s first routine service. This practice inevitably results in ruined turbos.

Presence of foreign objects. Sloppy assembly or workmanship during servicing may leave foreign objects, such as bolts, nuts, cigarette butts and cleaning rags, in the inlet tract. Contact between a rapidly spinning turbine wheel and a foreign object always results in a ruined turbo.

Dirty or contaminated motor oil. Dust or solid particles in the motor oil will cause rapid and extreme wear on the turbo shaft, ruining the oil seals and allowing oil to enter the inlet tract, causing excessive oil consumption and smoke emissions from the tailpipe. Water or coolant in the oil will have much the same effect due to the diminished lubricating ability of the oil.

Sticking wastegate. While this condition may not necessarily result in the destruction or failure of the turbo, a wastegate stuck in the open position will rob the turbo of its effectiveness. This is because the compressed air is dumped directly into the exhaust system, depriving the engine of the air it needs to work efficiently. Stuck in the closed position, the persistent pressure may rupture hoses or duct, also resulting in a dramatic loss of power.

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