Turbos have maintained a consistent presence in the automotive world, but there is a current surge in their popularity. They are now a prevalent feature in a wide range of vehicles, from high-revving Hondas to powerful diesel pickups and even factory Ford Mustangs. Despite the widespread adoption of turbos, failures are inevitable, especially in extreme operating conditions. Even with essential components like wastegates, blow-off valves, ball bearing center cartridges, and 360-degree thrust bearing assemblies, turbos can still be pushed to their limits and experience failure.
For those driving vehicles equipped with turbochargers, whether cars, trucks, SUVs, or any other wheeled transport, we present insights into potential weak points to help you navigate around them effectively.
1. Foreign Object Damage
Foreign Object Damage (FOD) poses a significant risk to turbochargers, as any foreign material that enters the system can lead to catastrophic failure. This includes debris such as dirt, dust, shop rags, or even bolts accidentally left in the intake. Shockingly, a staggering 80 percent of turbo failures can be attributed to external objects coming into contact with the compressor wheel's blades, particularly on the intake side. When a failure of this nature occurs, the leading edge of the compressor wheel's blades will bear evidence of the impact, and the inducer bore, where the compressor wheel is housed, may exhibit signs of contact or scarring.
One common culprit behind the infiltration of debris into a turbocharger is a dirty air filter. Neglecting the maintenance of this seemingly basic component in your vehicle can have costly consequences, potentially resulting in a four-figure expense for turbocharger replacement and even a five-figure one if any debris manages to enter the engine. Fortunately, in many modern turbocharged setups, an intercooler is employed to cool intake temperatures. This intercooler, positioned between the turbocharger and the engine, often acts as a safety net by trapping any fragments that break off from the compressor wheel, mitigating the damage caused by FOD incidents.
Solution：
Ensure optimal performance of your air filter by maintaining it properly: clean reusable filters regularly or replace disposable ones at recommended intervals.
2. Overspeeding
When a turbocharger surpasses its compressor map, it can result in a situation where additional boost may not be generated consistently. However, there is a high likelihood of excessive drive pressure being created, causing the shaft to experience speeds beyond its intended capacity. This overspeeding phenomenon can lead to detrimental consequences, with the exhaust wheel of the turbine typically being the initial component to fail. In some extreme cases, the turbocharger can disintegrate and forcefully exit through the tailpipe at an alarming velocity, presenting a potentially hazardous scenario.
Instances of overspeeding are notably prevalent in high-performance diesel vehicles. Even in their factory configuration, modern diesel trucks can reach boost levels of 30 psi or higher. With the addition of aftermarket modifications such as programmers and larger injectors, it becomes relatively easy to surpass the operational limits of the original equipment manufacturer (OEM) turbocharger.
In the diesel aftermarket sector, particularly within activities like sled pulling and drag racing, a single turbocharger can encounter boost pressures as substantial as 100 psi. An illustrative case involves a BorgWarner turbo based on the S400 series, which, when exposed to over 70 psi of boost along with a significant nitrous oxide injection and a malfunctioning external wastegate, experienced catastrophic overspeeding. The failure of the thrust bearing initiated excessive shaft movement, leading to the compressor wheel coming into contact with the housing and becoming lodged askew within the inducer bore, resulting in severe damage and operational failure.
Solution:
Maintaining a turbo's boost-to-drive pressure ratio at around 1:1 (or up to 1:1.5 in certain situations) is crucial for optimal performance. Achieving this balance might involve implementing a wastegate to regulate and release excess drive pressure or enhancing exhaust flow by installing a larger turbine housing. By fine-tuning these elements, you can enhance the efficiency and power delivery of your turbocharged system.
3. Oiling Issues
One of the critical issues that can significantly impact the performance and longevity of a journal bearing turbocharger is the lack of proper lubrication. Without adequate oil supply, the bearings within the turbocharger can deteriorate rapidly. Over time, this lack of lubrication can lead to shaft play, causing the compressor and turbine wheel to come into contact with their respective housings. Additionally, insufficient oil supply can result in scoring of the thrust bearing and introduce excessive heat that can compromise the turbocharger's central section.
To address the lubrication concerns, especially with larger frame turbos, it is advisable to utilise a -6 AN oil supply line as a minimum requirement. This ensures a consistent and appropriate flow of oil to the turbocharger, mitigating the risks associated with inadequate lubrication.
Furthermore, oil contamination poses another significant threat to the turbocharger's functionality. Contamination can arise from various sources such as improper maintenance, coolant or fuel mixing with the engine oil, or debris from internal engine components breaking down. Contaminated motor oil can lead to a range of issues similar to those caused by a lack of lubrication, including worn journal bearings, damaged thrust bearings, and shaft scoring. It is essential to prevent oil contamination to maintain the turbocharger's optimal performance and prevent costly damage in the long run.
Solution:
Ensure optimal performance by using a -6 AN oil supply line. Regularly change your engine oil to maintain its quality and ensure it is free from any contaminants. These steps are essential for keeping your engine running smoothly and efficiently.
4. Seal Leaks
When it comes to turbochargers, it is crucial to address any potential issues with seal leaks promptly. The majority of modern turbochargers utilise dynamic seals as opposed to carbon seals. These dynamic seals play a pivotal role in preventing the oil intended for the center section from seeping into either the intake (compressor) or exhaust side (turbine) of the turbocharger.
However, several factors can contribute to seal leaks, such as excessive crankcase pressure in high-performance engines, wear and tear on the seals due to prolonged use, or an incorrectly positioned or inadequately sized oil return line. If the center section of the turbocharger becomes excessively pressurised, it can result in the unwanted displacement of oil into both the intake and exhaust sides of the turbocharger. It is essential to address these issues promptly to maintain the optimal performance and longevity of the turbocharger system.
Solution:
For high horsepower applications causing excessive crankcase pressure or oil pressure, consider upgrading to a better crankcase ventilation system or a dry sump oiling system. If you are experiencing oil leaks from an aging turbocharger, it may be time for a thorough inspection and potential overhaul.
5. Thrust Bearing Failure
When discussing turbocharger components, it is essential to consider the role of the thrust bearing in maintaining optimal performance. The thrust bearing, positioned closest to the compressor wheel, plays a critical role in limiting end play within the turbocharger assembly. It is important to note that the standard end play range for efficient functioning typically falls between 0.002 to 0.004 inches.
The thrust bearing operates by relying on a thin film of oil to create a barrier between itself and the shaft. This lubrication is vital as any direct contact between the bearing and the shaft can lead to thrust bearing failure. Once this failure occurs, it often paves the way for wheel-to-housing contact issues.
It is worth noting that when a turbocharger is equipped with an aftermarket compressor wheel, particularly one that is larger and heavier than the original, the lifespan of the 270-degree thrust bearing is significantly reduced. This reduction in lifespan can have implications for the overall performance and longevity of the turbocharger unit. Therefore, it is crucial to consider the compatibility and potential impact of aftermarket components on the thrust bearing to avoid premature failure and ensure the turbocharger's optimal operation.
Solution:
Consider enhancing your turbo system by incorporating a 360-degree thrust bearing or selecting a unit with a 360-degree thrust option for optimal performance and reliability.
6. Surging
Compressor surge, also known as turbo bark or chirp, is a phenomenon where intake air reverses back out of the compressor. This typically occurs when there is a sudden cut-off of elevated boost, such as when the throttle is lifted abruptly. The noise accompanying this event is caused by the compressed air being trapped in the intake system, with no outlet other than backtracking through the turbo. Surging can be particularly damaging to the compressor end of the turbo, with prolonged occurrences leading to significant wear on the thrust bearing. To mitigate the risks associated with surging, blow-off valves are often employed in high-surge applications.
The most severe cases of turbo surge are often found in vehicles that are over-turbocharged, where a turbocharger has been incorrectly specified for the application. For example, in a 12-valve 5.9L Cummins-equipped Dodge Ram fitted with a 71 mm BorgWarner S400 turbo, originally designed for a smaller turbo in the 54-56 mm range, significant surge occurs at lower engine speeds. In this setup, the turbocharger operates consistently within the surge line, leading to a diminished service life and potential catastrophic failure due to the stress induced on the compressor wheel.
Solution:
Select the perfect turbo size for your engine to maintain optimal performance across all RPM ranges. Avoid going oversized to prevent surging at low RPMs and overspeeding at high speeds.
7. Extreme Heat
When it comes to turbochargers, extreme heat is a critical factor that can impact their performance and longevity. Turbochargers are designed to withstand high temperatures, but prolonged exposure to 2,000 degrees Fahrenheit can ultimately lead to issues on the turbine (exhaust) side of the turbo.
Common failure points attributed to excessive heat include stress cracks in the turbine inlet flange, eroded edges of the turbine inlet volutes, and deformation of the tips of the turbine wheel blades. These issues can arise due to various factors such as high performance demands, a restricted exhaust system, a cracked intercooler, or even a clogged air filter.
While turbochargers are resilient components, it's essential to note that heat-related damage can extend beyond the turbo itself. Excessive heat can potentially harm internal engine components like valves or pistons before causing significant damage to the turbocharger's Inconel turbine wheel. Although such occurrences are infrequent, it's crucial to be aware of the impact of extreme heat on turbocharger performance and the overall engine system.
Solution:
Monitor your exhaust gas temperature with a pyrometer gauge to ensure you're operating within the optimal heat range for your engine and application.
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