10 Reasons a Turbo Leaks Oil (and then smokes)
Turbochargers are a fantastic way to add HUGE power to any powerplant, however, if the system is not designed properly you can spend a lot of time and money repairing turbos and chasing issues. Today we are going to cover why turbochargers smoke, how their seals work, and what are some of the root causes.
Turbo Oil Seals
Before we dive in, I want to make sure everyone is on the same page of how a turbo oil seal works. It is actually not a seal at all as you would expect. A turbo oil seal (there are two, one on the compressor side and one on the exhaust side) is actually most similar to a gapless piston ring. I know, a lot of people think or imagine them as a transmission seal, but they are not. This means that high tolerance machining and a metal ring riding on that machined surface is what keeps oil from getting out of the center bearing cartridge. Now we can dive into some of those issues and causes.
1. Too Small of Feed Line: Each turbo and turbo bearing style will require a different amount of oil flow to operate properly. A journal bearing uses more oil as the shaft rides on a thin layer of oil between the bearing and the shaft. A ball bearing turbo uses less oil, which is why often times ball bearing turbos have a restrictor installed from the factory. Generally a true T3 or T4 turbo will require a 4AN feed, whereas a T5, T6 or Promod / Large Frame turbo will require a 6AN feed. Of course there are deviations to the above, but those are general rules of thumb.
2. Too Small of a Return Line: Each Turbo will need a different size return line. Typically on a T4 or Mid Frame Turbo we run 10AN return line. Whereas a T5 or T6 turbo of mid frame or larger will need a 12AN return. Note: You can NOT over size a return or drain line. The more oil and more more efficient it returns oil to the pan the better. Also, please note that not all drain flanges are created equal. Just because a 10AN fitting fits on a drain flange does not mean the ID is big enough. We have seen a lot of small ID (in comparison to the standard spec) and this becomes a traffic jam restriction for all oil trying to leave the bearing cartridge.
3. Incorrectly Routed / Built Return Line: You can not simply connect the drain line back to the oil pan without consideration and understanding on what works and what does not. DO make sure the line is on a constant downhill path to the oil pan. Flat spots, uphill routing, and "whoops" in the line can and will cause issues. In the event you can not properly route the line, it is time to look at an oil scavenge pump. These pumps use suction to evacuate high temp oil from drain lines and will pump vertically and horizontally to keep the drain line clear. Note, different turbos will require different size pumps. More info can be found searching
4. Too much oil pressure: This one goes without saying. Too much pressure can cause seal failure. Too much pressure can also highlight and expose other issues in the drain system.
5. Blown Cold Side Coupler Under Boost / Stretched Shaft: This little known fact can explain a lot of turbo issues. We see this several times a year. When a silicone coupler or Vband O-ring etc fail at large pressure levels and when the turbo is spinning high RPM, it can send a turbo shaft spinning from its operating range to double or triple. When the turbo overspins like this, the shaft can actually stretch. Knowing that the precision machined bearing shaft is ground and rides on a steel ring as a seal. It does not take much stretching to put the shaft out of tolerance which then creates the Exxon Valdez of oil leaks.
6. Too much angle on center bearing cartridge: Most bearing cartridges can be tilted 15-20 degrees one way or another. Of course flat is always going to be better. However, high degree of tilt can and will cause issues. This will create a condition similar to having too small of a drain flange. Think about how hard the oil is to leave the drain flange if the tilt is too much and the oil can not access that orifice to leave the center bearing cartridge.
7. Oil Drain Gasket / RTV blocking oil return on drain outlet: We made a tech tip Tuesday Product spotlight on this. We all know someone who is a little heavy handed with the RTV gasket maker. For some, the heavy handed one is who is reading this (I am not perfect). A very small amount is needed to seal two machined surfaces together. The rest gets pushed outward as well ass inward (drying and creating a blockage in the drain orifice on the bearing cartridge). For this reason we created a product for our line that has a machined in reusable high temp O-ring. Both t4 and t5 / t6 versions are available.
For more info on turbo drain flange and issues, watch this video.
8. High Back Pressure: This can prematurely wear out the thrust bearing in the turbo. Back pressure is the amount of pressure on the turbine inlet side of the turbo (headers, crossover, turbine inlet). Typical backpressure is 2:1 or less. Give or take of course. Back pressures elevated highly above these numbers can create forces inside of the bearing cartridge. This can cause bearing issues and of course thrust and bearing issues can cause shaft damage which then effects the seals.
9. High Crank Case Pressure (preventing oil from draining back into the pan): Built up crank case pressure literally is a force working against oil draining from the turbo into the oil pan. Think about it. No, you do not need a vacuum pump, but a properly sized and high flow catch can / breather package will be completely sufficient.
For a list of our catch cans for accomplishing removing crank case pressure, follow this link.
10. Contaminated Oil Causing Shaft Play / Excessive Bearing Wear: Just like in the engine that the turbo is powering.
When Did your Turbo start smoking?
Instantly upon startup? This could be improper system design (check all of the above first), or it could also be a poorly manufactured or defective unit.
After use? Most commonly a result of one of the above issues.
Options for repair?
Just because you have a smoking turbo, doesn't mean you need to go out and get a new one. Your original manufacturer will typically have an RMA or Repair Program. Also there are other companies that specialize in this service also. Listed below.
DON'T FORGET: Before you reinstall your new or repaired turbo, make sure you have addressed the root cause.