While they’ve never really been out of style, it’s no secret that turbos are “in” right now. You can literally find one on everything from 10,000-rpm Hondas and diesel pickups to big block street cars and factory Ford Mustangs. But with so many different types of vehicles benefitting from this blissful form of forced induction, there are bound to be failures. And in some extreme operating environments, not even insurance items such as wastegates, blow-off valves, ball bearing center cartridges, or 360-degree thrust bearing assemblies can keep a turbo from reaching its breaking point.
So if you’re rocking a turbo’d car, truck, SUV or anything else on wheels, we’ll show you these breaking points so you can sidestep them.
1. Foreign Object Damage
Anytime a turbocharger ingests something — be it dirt, dust, a shop rag or a bolt left in the intake — it can spell disaster. Unfortunately, outside debris making its way across the blades of a compressor wheel (the intake side) accounts for 80 percent of all turbo failures. When this failure occurs, the leading edge of the compressor wheel’s blades will indicate any impact from the object(s), and the inducer bore (what the compressor wheel sits in) may show signs of contact or scarring. In the photo below, an IHI turbo off of an LB7 Duramax diesel fell victim to a bolt being left in the intake.
The most common cause of debris infiltrating a turbo? A dirty air filter. That’s right, lack of maintenance on one of the most basic components on your vehicle can cost you a four-digit figure (turbo) and potentially a five-digit one if any shrapnel makes its way into the engine. Fortunately, being that most modern turbocharged applications utilize an intercooler (a heat exchanger positioned between the turbo and engine) to cool intake temps, it often becomes the catchall for compressor wheel fragments.
SOLUTION:
Run a quality air filter with an outerwear, keep it clean if it’s reusable or install a new one at the proper interval if it’s replaceable.
2. Overspeeding
Once a turbo is pushed out of its compressor map, it may not always produce more boost, but it will almost always create excess drive pressure, causing the shaft to see more speed than it was designed to handle. When overspeeding occurs, the turbine (exhaust) wheel is usually the first component to give way, and we’ve even seen a few come apart and exit the tailpipe at the speed of light (scary!). In particular, overspeed scenarios are somewhat common on high performance diesels. Even in completely stock form, a modern diesel pickup can see 30 psi of boost or more, and it doesn’t take much in terms of power-adders to exceed the limitations of the OEM charger (namely programmers and/or larger injectors).
In the diesel aftermarket (where sled pulling and drag racing is extremely popular), a single turbocharger can see as much as 100 psi of boost. When the S400 based BorgWarner turbo below was subjected to more than 70 psi of boost, followed by a big shot of nitrous and an external wastegate that failed to open, catastrophic overspeeding occurred. The thrust bearing checked out, which led to excessive shaft play followed by the compressor wheel making contact with the housing and effectively wedging itself sideways in the inducer bore.
SOLUTION:
Keep your turbo’s boost-to-drive pressure ratio as close to 1:1 as possible (1:1.5 is OK in most cases), which may entail running a wastegate to bleed off excess drive pressure or opening up the exhaust flow via a larger turbine housing.
3. Oiling Issues
Lack of proper lubrication (oil supply) will kill the bearings in a journal bearing turbocharger in short order. When subjected to a lack of oil supply for extended periods of time, the journal bearings will eventually begin to allow shaft play, followed by the compressor and/or turbine wheel making contact with its respective housing. Inadequate oil supply can also score the thrust bearing, as well as introduce excessive heat for the center section to deal with. On larger frame turbos, it’s recommended to use a -6 AN oil supply line (at a minimum) to ensure appropriate oil flow is always on tap.
Oil contamination — be it from lack of maintenance, coolant or fuel in the engine oil or debris from an internal engine component breaking down — can wreak havoc on a turbocharger as well. Corrupt motor oil can lead to all of the problems mentioned above (worn journal bearings, a damaged thrust bearing, or scoring of the shaft), less the super-heating of the turbocharger’s bearings. A scored shaft from a Garrett TP38 turbo (due to contaminated engine oil) is shown below.
SOLUTION:
Run no smaller than a -6 AN oil supply line, make sure your engine oil is changed regularly and is always free of contaminants.
4. Seal Leaks
Most modern turbochargers make use of dynamic seals (vs. carbon seals), which keep the oil being supplied to the center section from making its way into the intake (compressor) or exhaust side (turbine) of the turbo. However, things like excessive crankcase pressure in high horsepower engines, operational wear on the seals or an improperly routed (or undersized) oil return line can lead to oil leaks. Once the center section becomes overly pressurized, it can push oil into the intake and/or exhaust side of the turbo.
SOLUTION:
If you’re running excessive crankcase pressure or oil pressure due to a high horsepower application, a better crankcase ventilation system or a dry sump oiling system should be looked into. If you’re pushing oil from an old turbocharger, it may be time for an overhaul.
5. Thrust Bearing Failure
The thrust bearing is located nearest the compressor wheel. Its job is to limit end play (and we’ll note that typical end play should be between 0.002 to 0.004 inches). Because this bearing rides on a thin film of oil between it and shaft, it is crucial that the bearing doesn’t come in contact with the shaft. Once contact occurs (such as in the 270-degree thrust bearing application in the midst of a rebuild shown below), thrust bearing failure is usually imminent. And once the thrust bearing is gone, wheel-to-housing contact is soon to follow. Anytime a turbo is fitted with an aftermarket (often bigger, and heavier) compressor wheel, a 270-degree thrust bearing’s lifespan is shortened considerably.
One of the best ways to improve the durability of a turbocharger is to add a 360-degree thrust bearing (right), which provides a full circle of oil lubrication around the shaft (vs. 75 percent with a 270-degree unit, left). The 360-degree bearing pictured below comes standard in all of High Tech Turbo’s S365 forged milled wheel (FMW) turbochargers, which are based on the S366 unit offered from BorgWarner. The company dissects the box turbos and scraps the factory, 3-pad 270-degree thrust in favor of the 6-pad unit pictured on the right.
SOLUTION:
For insurance (and whenever possible), add a 360-degree thrust bearing to your turbo or specify a 360-degree thrust option when purchasing a new unit.
6. Surging
Also referred to as turbo bark or chirp, compressor surge occurs when intake air actually reverts back out of the compressor. It’s most often experienced when elevated boost is produced and then cut off abruptly (i.e., you lift off the throttle suddenly). The noise you hear is the compressed air trapped in the intake that has nowhere else to go but back out the way it entered the turbo. Surging is extremely hard on the compressor end of the turbo, and prolonged surging will eventually beat the thrust bearing to death. Blow-off valves are commonly used in high-surge applications. If violent enough, surging can literally explode a compressor wheel (see below).
The worst cases of turbo surge are common on over-turbo’d vehicles (i.e., applications where a turbocharger has been improperly spec’d). For instance, a 12-valve 5.9L Cummins-equipped Dodge Ram sporting a 71 mm BorgWarner S400. Because this engine was designed to utilize a 54-to-56 mm turbo, a unit with a much larger compressor (and turbine) wheel will experience considerable surge at lower engine speed. In this configuration, the turbo will nearly always be in the meat of the surge line, and it will never enjoy a lengthy service life.
SOLUTION:
Spec a properly sized turbo for your engine (i.e., don’t go too big) to ensure you stay above the surge line at low rpm and out of the overspeed zone on the top end.
7. Extreme Heat
Extreme heat can kill anything, right? Well, the same goes for turbochargers. Prolonged exposure to 2,000 degrees Fahrenheit will eventually take its toll on the turbine (exhaust) side of the turbo. Common failure points due to heat are: stress cracks in the turbine inlet flange, eroded edges of the turbine inlet volutes (pictured below) and deformation of the tips of the turbine wheel blades.
Common causes of excess heat being generated include: high performance, a restricted exhaust system, cracked intercooler, or even a clogged air filter. It’s been our experience that heat will damage something internally in the engine (a valve, a piston, etc.) before it can do considerable damage to an Inconel turbine wheel. Still, it happens on occasion.
SOLUTION:
Install a pyrometer gauge to keep an eye on exhaust gas temperature, and stay within the recommended heat threshold for your particular engine/application.