By Greg Arsenault
Below are the most common failure modes of turbochargers:
1. Contaminated oil
2. Lack of oil
3. Foreign debris in air stream
4. Excessive heat/friction
5. Hot shut downs
6. Physical contact of rotating components within the housing
Although the above list is well known within the industry, it is worth taking a second look periodically to ensure the best performance and longest lasting turbos.
In a perfect world the, turbo should last as long as the engine. Unfortunately, we don’t live in a perfect world. Replacing a turbo is expensive. If we do not find out the specific reason the turbo failed, the replacement turbo is apt to wear out at a much more quickly than it should.
The # 1 killer of turbos is contaminated or dirty oil.
This is even more critical in gasoline engines where temperatures can be up to 1800 degrees Fahrenheit with speeds up to 300,000 RPM – as compared to only 1200 degrees Fahrenheit and 100,000 RPM for a typical diesel application. The failures occur in a similar manner, regardless of the source of ignition, and usually at differing rates.
The typical turbo shaft spins in two journal bearings. These bearings, made of a brass composite/alloy, are not fixed – they spin at theoretically half the speed of the shaft. As the dirty oil is introduced in a very narrow band through the holes in the rotating bearing, the holes score and wear the bearings due. As the wear progresses, both the inside and outside diameters of the bearing are opened, allowing the shaft to “wobble” from excessive radial clearance. This is clearly seen in the bearing on the right in the photo below. Once this clearance is large enough for the shaft/wheel assembly to become out of balance or touch the housing (while rotating at 100,000 RPM or more), a catastrophic failure is imminent.
This is why you should always require your customers to change the oil and filters and provide proof of the changes or risk a voided warranty.
The other failure modes are closely related, and we will discuss them in future articles.