I doubt many people have given much thought as to how and when the turbocharger was born. I won’t bore you with the details but know that it happened way back in the early 1900s. Once it was discovered how much additional power a turbo can provide, their applications for use continually grew. You can imagine the number of design changes they have seen over the years, and they are still undergoing as time creeps along. Revisions typically mean improvements in one way or another. However, just like diesel engines, some designs have proven better than others.
We decided to shed some light on some common ways a turbo can fail and what can be done to prevent that failure. If you would like to protect an expensive and vital engine component then read on as Nate Brekken, co-owner of Strictly Diesel disassembles a pair of turbos for inspection.
Looking at how a turbo operates, they’re pretty simple. Exhaust pressure is used to spin the turbine wheel which causes the compressor wheel to spin at the same speed. The compressor wheel is used to pull air through the air filter and then into the compressor housing. The air is then compressed, sent through the intake manifold, and then into the engine. As you zoom in closer, things get much more complicated and sensitive.
They’re The Same, But Different
There are two main categories of turbos, and while sharing many of the same components, they have some major differences as well. The first and more traditional turbo design is referred to as a fixed vane or fixed geometry turbocharger. These were found in diesel engines before they were equipped with emissions equipment like EGR valves and coolers. This style of turbo does not suffer from soot buildup on the exhaust side since the only moving part is the turbine wheel. They do not have components like vane actuators or vane position sensors, unison rings, vanes, or vane cages. For that reason, many feel these are more reliable units.
The second design, which you’ll find on modern diesel engines, is referred to as a variable vane turbocharger (VVT) or a variable geometry turbocharger (VGT). These two are essentially the same thing and you’ll commonly hear them referred to as one or another. Both of them have either individual vanes or a vane cage inside of the exhaust housing that opens or closes to alter the exhaust housing’s Area over Radius (A/R) ratio. By creating a lower effective A/R ratio, the vanes help the turbo build boost sooner. By “opening up” the vanes, this creates a larger effective A/R ratio allowing for better top-end performance. They offer many other benefits and are almost a necessity with strict emission requirements. Two common examples of these include Garrett turbochargers that have vanes that open or close whereas Holset uses a cage that moves in and out.
Failure On The Exhaust Side
Through normal driving, soot will flow through the exhaust housing, and over time it can build up, leading to problems. Typically, this is seen in trucks that live a very easy life with little to no towing or hauling, and not a lot of heat being generated. Although this type of usage may net better fuel economy, the downside is problems are created in the vanes. If the vanes don’t see a full range of frequent movement or heat, then soot deposits can build up and block their range of motion and cause a turbo failure. In some cases, it can cause the vanes, unison ring, or cage to seize in one position. Your truck will recognize this very quickly and set a check engine light.
Depending on the position they are stuck will cause either a lack of low-end or top-end power. When this happens, it might be possible to remove and clean the turbo, but depending on internal wear or its age and mileage, it may be best to have it replaced. More-than-normal soot build-up can however be caused by other things like boost leaks, exhaust leaks before the turbo, or tuning with a low focus on smoke control. The good news is, there are some ways to help prevent this. Keeping the vanes moving is the goal, which can be done by enjoying some spirited acceleration runs, using the turbo brake, and of course, making sure the engine is mechanically sound. Towing will help this situation as well since the vanes will be cycling back and forth.
Death By Fire
Since turbos use exhaust flow to function, they see a tremendous amount of heat. For those of you who monitor exhaust gas temperatures (EGTs) and tow heavy loads, you’ve seen firsthand how this number impacts your cooling system. EGTs can also impact your engine’s turbo, and this is frequently forgotten. High temperatures can result in damage to the turbine wheel and can be seen by an orange peel appearance or rippling on the fins of the turbine. Another indicator is when the metal has folded over and melted away. Melting metal off of the turbine wheel may seem like a stretch, but when metal is missing and there’s no evidence of contact inside the exhaust housing it’s pretty clear what happened.
Metal is a great conductor of heat, so it’s easy for it to transfer into the bearings. Turbochargers use a thrust bearing to limit how far the rotating assembly can move from side to side. The journal bearings allow the rotating assembly to spin, and these are generally brass bearings that ride on the center of the shaft. As heat makes its way in, signs of it can be seen by discolored metal components. You may see where brass material from the bearings has transferred onto the shaft, or created darker areas that can appear black and burnt or blue in color. If EGTs are too high for too long, this can begin to melt the bearings and plug the oiling holes built into them. If there’s no film of oil to keep them lubricated, the wheel may be difficult to spin by hand or it could seize and not spin at all.
This is why monitoring exhaust temperature is so important. Pyrometers allow you to see, in real-time, the heat being generated which can be an indicator of how hard you’re pushing the turbocharger. There are a lot of factors that cause high EGTs, but here are some tips. First, don’t lug the engine when towing heavy loads. Even though the engine may have the power to run with low boost pressure and move the load, low airflow means higher EGTs. Keeping the engine RPM up will raise boost, increasing airflow into the engine. This in turn decreases EGTs. This is not always enough, so you may find yourself having to slow down and downshift. Moving a loaded trailer shaped like a brick, with a headwind may prove too much to maintain speed with the rest of traffic. It’s best to make the engine and turbo work, just not past its efficiency range to the point of failure.
Bearings Prefer Clean Oil
As mentioned above, bearings can fail due to heat. They can also fail due to a lack of lubrication or contamination. When a turbo fails and is disassembled, the bearings can paint a clear picture. If there is any foreign debris in the engine oil, it may plug the oil passages starving it of oil. This contamination could also make its way into the bearings and cause scarring or other wear marks. Excessive wear to the bearings can cause the rotating assembly to be out of balance or have excessive lateral or vertical movement. Eventually, it can be severe enough to allow one or both of the wheels to contact the housing.
Good maintenance is the key to preventing turbo failure. Oil change interval recommendations vary from one person or manufacturer to the next. Unless you’re running a bypass filter or fine-mesh filter, we don’t recommend extended drain intervals. It’s personal preference and it’s your truck so do as you please, but oil changes every 5,000 miles are much less expensive than replacing an engine. Turbos aren’t cheap either. Another great piece of insurance is a magnet around the oil filter. Filtermag makes curved magnets that stick to the side of the filter and work very well at trapping metal and preventing it from circulating throughout the oiling system. Whatever you do, make it a point to keep clean oil in your engine to keep it and the turbo healthy.
Filters And Air Intakes
Just like needing clean oil, your turbo needs clean air — and lots of it. A few different problems exist around filters and air intakes. The obvious is poor air filtration. Any dust or debris that makes its way through the filter will contact the compressor wheel. This will have a sandblasting effect and over time it will wear away the outer edges of the wheel. Upgraded billet wheels have a softer metal than factory ones and can be more easily damaged. This can lead to an unbalanced assembly as well as reduce the air it pulls through the intake. Less air means reduced efficiency and circles back to increased EGTs. The next problem is air restriction most commonly seen by dirty and plugged air filters. Trucks with performance tuning that run a factory air filter can run into this as well. A restrictive filter can cause an overspeed situation taking it beyond its operating limits. This force can overcome the film of oil on the thrust bearing and cause the rotating assembly to be pulled far enough in a direction allowing it to contact the housing.
Aftermarket air intakes generally improve airflow over the stock setup, but make sure you choose one that uses a quality filter. Not all are created equal. When the right engineering has gone into a kit you’ll find ISO test results, intake temperatures drop, and CFM improvements compared to a stock intake. If you decide to run a larger-than-stock turbocharger then plan on ditching the factory intake to allow your turbo to breathe in a lot of clean air.
Overall, turbochargers can be very reliable units as long as they’re properly cared for. This can come in the form of changing your driving habits, being proactive with maintenance, using quality parts, and making sure you have the right setup for your use and your turbocharger. Remember that turbos don’t normally fail on their own so don’t shoot the messenger.