It’s no secret that forced induction is a proven method to yield big increases in engine output. By forcing more air into the combustion chamber, an engine can function more efficiently and in turn provide more power. Either supercharging or turbocharging can provide this benefit to an engine; superchargers are belt-driven and are therefore operating whenever the engine is running, while a turbocharger is driven by the exhaust gases that the engine generates as it builds revs throughout the powerband.
The turbocharger does not have the same parasitic loss a supercharger does, and for that reason, turbocharging has become an increasingly popular choice for OEMs looking to improve power output, fuel economy, and emissions over similarly powerful, larger-displacement naturally-aspirated or supercharged engines. But while turbos commonly offer increased efficiency as well as a clear path for tuning to make more power, they also bring with them an added amount of complexity that can be a bit daunting for the uninitiated.
Here we’ll check out some of the most frequently encountered issues that befall turbochargers with some insight from the experts at Mahle–suppliers for many OEM turbochargers–about how to deal with these issues when they arise and steps you can take to prevent this kind of damage from happening in the first place.
Turbochargers are asked to deal with pressure, heat, and high-speed operation amid a tightly-controlled environment, so their longevity is largely dependent on a steady supply of oil to keep the bearing section properly lubricated and cooled.
“Without a doubt, the most common problem we see killing turbochargers is a general lack of engine maintenance,” says Mahle’s Larry Ireland. “People who just don’t change their oil and it gums up. That often ends up clogging the return line, which means the turbo can’t return its oil and it starts leaking.”
When you also consider the fact that a turbocharger is a precision device with parts that operate at high speed, it’s clear that anything which compromises the functions of those moving parts will take a toll on the turbo in very short order. “That old, gritty oil running through the bearings can also take out the shaft or/and allow the impeller to hit the inside of the turbo housing,” Ireland explains. “A lot of the inadequate oiling issues that we see on light vehicle applications involves a screen that OEMs often put on the oil fill to the turbo – that screen gets clogged up then the turbo isn’t getting proper oil flow, and that’s the sort of thing that can quickly cause failures.”
Impeller damage caused by contact with the turbo housing. On the right, we can see a broken shaft shank, which is usually caused by operating the turbocharger for a prolonged time without enough oil. The shaft material can thus burn
out and break due to the friction between the shaft and the bearings.
Fortunately for those running turbocharged engines – particularly in OEM applications – the formula for damage prevention is pretty straightforward. “Ultimately you want to try and follow a manufacturer’s recommendations as closely as possible,” Ireland says. “If an automaker recommends an oil change every 5,000 miles, that might not be just for the sake of engine internals. Because of the tight tolerances in an engine bay, it’s not really feasible for a manufacturer to expect consumers to check the turbo and its lines for issues, so the best insurance is really just to stick to the recommended oil filter and air filter replacement schedules.”
As far as the type of oil to use in turbocharged engines, Ireland suggests that the OE is the best source here as well; they have spent the time to engineer the products to work together properly.
“A lot of the early turbo engines that we were seeing for light vehicles ran a full synthetic,” he told us. “Now that’s not really the case – these days a lot of manufacturers specify a semi-synthetic. The important thing is just to not ignore those oil recommendations from the OE, both in terms of type of oil and viscosity.”
Foreign Object Damage
Because of the extremely high speeds where turbochargers operate best, introducing debris into the mix can lead to catastrophic turbocharger damage, and can potentially hurt the charge air cooler as well. This isn’t so much an issue of debris from the outside world mingling with the workings of the turbocharger, though.
If the return line becomes clogged, the oil can no longer flow out and oil is forced out of the turbocharger itself as a result.
“You see this more on the heavy-duty vehicle side of things,” Ireland says.
“For instance, on a diesel engine what often happens is an injector tip will break off. That tip has to go somewhere, and it usually goes through the exhaust valve, out the exhaust, ends up in the turbine side of the turbocharger, and takes off that turbine wheel.”
Preventing this kind of damage is a bit trickier though – more often than not, the culprit ends up being maintenance or repairs that have been performed without adequate cleanup afterward.
Foreign object damage can cause issues without a complete turbo failure. The damaged vane on this impeller will significantly reduce the turbo’s efficiency.
“A lot of the debris we see in these cases is because they’ve had an engine failure and the systems that feed the turbo weren’t properly cleaned afterward,” Ireland says.
“Intercooler, charged air piping, even inside the head – if they don’t get all the debris out it’s just floating around, it can go either way through the intake or the exhaust. We also see a lot of cases of folks going mudding, removing the air cleaner, and that obviously allows dirt and water to get sucked into the systems. But usually if it’s a debris issue, it stems from a previous failure if it’s on the intake side of the turbo. If it’s a failure that’s currently happening at the time, that usually affects the exhaust side of the turbo.”
Because of the high speeds turbochargers see, it can be tough to prevent serious damage once it becomes clear that something’s amiss. Ireland recommends simply shutting down the engine at the first sign of an issue and not operating it again until you’ve had a chance to get in there and clean out the systems of any debris.
An overabundance of heat is never a desired condition for any engine components, and turbochargers are of course no exception. And like any other engine component, turbochargers are designed to function within a specified range of temperatures – exceed that and you run the risk of causing some problems.
The most common issue associated with excess heat and turbochargers is housing damage.
“You have a lot of expansion and contraction happening on the turbine side because that’s where all your exhaust heat is,” says Ireland.
“Then you shut down the engine and it cools down and contracts quickly. Doing that repeatedly can eventually lead the metal to fatigue over time and cause cracks in the housing. Sometimes it’s not even an issue of operating the turbocharger outside its specified range – sometimes it’s just a problem with the actual design of the housing.”
Cracks in the turbo housing like this can be caused not only by excess heat but simply by bad housing designs, which can see this kind of damage over time from metal fatigue in areas where the housing material is especially thin.
For high performance applications, it’s wise to allow the engine to cool down gradually after high stress use – like a proper cool-down lap after a lapping session on a road course, for instance.
Sticking To The Program
At the end of the day, many of the issues that arise with turbochargers can be mitigated by working within the specifications provided by the manufacturer and ensuring that the turbo is getting proper lubrication in a contaminant-free environment.
Signs of foreign substance impact on the air guide plates of the VTG unit and in the intake passage of the compressor housing.
“Make sure none of the lines are getting kinked or rubbed on,” Ireland says.
“Ignoring that sort of thing can lead to leaks and much bigger issues down the road. And if a customer is in the process of replacing a turbo, it’s important to not only clean the charge air cooler and charge air lines, they also need to clean their oil feed and drain lines to make sure that stuff is clear. Even on light vehicle engines, buildup in the lines can start to develop and it can restrict oil flow, either to turbo or out of it, which can be detrimental to the turbo either way.”
Ireland says that these lines can usually be cleaned by simply running a parts washing solution through the affected lines and scrubbing them down with a wire brush, but replacing them altogether is also worth considering if it seems like they’re too far gone.