Determining the cause of turbo failures is important to keep the failure from reoccurring. We often disassemble turbochargers to determine why they failed. Once a turbo is disassembled and components are inspected it is easy to determine a cause. Turbochargers for most diesel applications rotate up to 150,000 rpm or higher, some applications may rotate as fast as 360,000 rpm. See more on how turbos operate on our FAQ page
Looking at some turbo failures you may see the wheels have rubbed the housings, and the side play is extremely loose. It may appear the bearings have failed and allowed the wheels to hit the housings. The bearings are usually made of a brass composite alloy however, some are ball bearing. Bearings fail due to other causes, not because of a bad bearing. The primary cause of failure must be determined, as secondary failures are likely to happen once the bearings are damaged.
The following failure analysis is based upon the use of a high quality turbo manufactured by Garrett, Borg Warner, Holset, IHI, or Mitsubishi. Cheap aftermarket turbos may not meet quality standards and failure analysis of poor quality product may be more difficult to perform.
Most turbos use full floating bearings, the bearing floats on a film of oil and theoretically rotates about half turbine wheel shaft speed. The most common turbo failure causes are as follows:
Contaminated oil or dirty oil
Contaminated oil leaves radial scratches or grooves on the bearings and bearing housing. We often hear people state that their engine bearings are not this bad, so it must be a turbo fault. Remember the turbo is turning 50 times faster than the engine, 2000 miles on the turbo is like 100,000 miles on the engine bearings.
Scoring on the thrust bearing from contaminated oil
Scoring on the turbine wheel side bearing will be worse due to the heavier weight to the turbine wheel. Notice the bearing is also deformed and worn down smaller in diameter than the compressor side bearing.
Coolant in the oil will also damage turbo bearings and thrust washers. Always change the engine oil when replacing a turbocharger.
Lack of Oil or Oil Starvation
Oil lubricates and cools the turbocharger, The specified oil at the correct viscosity is required to keep a turbo alive. Some turbos use water cooling to help keep oil temperatures down. Lack of oil, or oil starvation results in extreme oil temperatures and bluing of overheated metal and burnt oil. Material transfer, due to excessive friction, and excess wear to bearings and thrust surfaces are other signs.
Oil starvation will often cause bearing failure and wheel contact with the housings.
When components are overheated this is a sure sign of lack of lubrication. Even as little as 2-3 seconds with no oil can overheat turbocharger components, causing a failure. Turbos that have failed due to another cause will never show signs of overheating, if they had sufficient oil supply.
Thrust surfaces show bluing, from overheat, which is a lack of lubrication.
You can also see material transfer to the turbine wheel shaft from the bearing.
Visible bluing and metal transfer on the turbo components.
Low oil levels, incorrect grade of oil, fuel dilution, low oil pressure, restricted oil feed line, hot shutdowns, and incorrect priming procedure can cause oil starvation damage. The following are the results and causes of lack of oil.
- Severe shaft discoloration, normally on the turbine end
- Journal bearing discoloration
- Journal bearings seized to the turbine shaft
- Journal bearing hammered out
- Thrust bearing wear and discoloration
- Shaft fracture, typically at the turbine end
- The causes of lack of lubrication can include:
- Initial run without first priming the turbo with oil, known as “oil lag”
- Poor oil filter maintenance or excessive change intervals
- Damaged, kinked or collapsed oil supply line
- Insufficient oil in the sump
- Sealing compounds such as Teflon tape, or silicone sealant blocking the oil inlet, oil feed line, or internal turbo oil passages.
- Sludge or coke buildup in bearing housing from hot shutdowns
Foreign material or Impact damage
Foreign material in the air intake system can damage the compressor wheel. Loose parts in the exhaust feeding the turbo, or parts from inside the engine will also damage the turbo. Damage to the turbine or compressor wheel will cause rotational balance issues and wheel contact is often a result.
A nut or rivet head, that is loose in the intake can cause this kind of damage. We had a customer that found one loose screw in the intake, causing this kind of damage. However, a second loose piece had been bounced back into the air filter. The piece came out later out (the air filter had impact damage internally) and damaged the replacement turbo.
A nut was dropped in the exhaust manifold to cause this damage. Aluminum piston material, from an engine failure will often melt and stick to the turbine wheel. This damage should not be confused with wheel rub, which will be uniform wear.
Wheel rub will often cause the compressor wheel nut to back off, this is a result of the wheel rub, not the cause.
Oil Leaks from the end housings
Compressor wheel rub, due to damaged bearing.
- If the bearings have failed and allowed wheel rub, and oil will leak past the seals. If the wheels have not contacted the housings then look for other causes.
- Oil leaks can be caused by pressure build-up in the crankcase or oil sump. This will restrict the oil flow from the turbocharger oil outlet where the pressure pushes the oil back into the bearing housing.
- High oil level in the crankcase, or a restricted oil return
- Restricted air intake system also causes oil leakage from the compressor end.
- Use of silicone on oil outlets will restrict the oil flow back to the oil crankcase.
Excessive fueling or blocking the wastegate can cause the turbocharger to over speed. Overspeeding is a term used when a turbo is operating well above its normal operating limits. If there are any leaks, cracks or poor seals between the compressor and the engine, the turbo will have to work harder and spin faster than it should to deliver the required air levels to the engine. Overspeed can result in compressor wheel burst, or the turbine wheel to separate from the shaft.
Orange peel effect is a sign of overspeeding.
Turbine wheel separation from the shaft may be another sign of overspeed. We often see this type of failure on Dodge Cummins 2004.5 – 2007 due to stock turbos and hot tunes. Matching the turbo to the fueling will keep from overspeeding the turbocharger.
Excessive Exhaust Temperatures
Excessive exhaust temperature can be caused by intake leaks, low boost, over fueling, restricted exhaust. This will often show up as cast components cracking, such as the exhaust manifold or the turbine housing.
To summarize for a turbocharger oil quality and volume is critical. Intake or exhaust leaks increase EGT, effectively the same as over fueling. Performance tunes without matching the proper turbo may cause overspeed and overheating. If you have a turbo failure, determine the cause in order to resolve the issue.