The Most Common Response People say is Turbo Seals are Bad, But Im Going to Teach You in This Post That Often this is the most Uneducated Answer. Here is a list of Most Common Problems to Least Common in Order.  In This List a Lot of the Time The Turbo Can Still Be “Good” But Blowing Oil.

The Top Reasons Why a Turbo Blows OIl:

1. The Oil Drain Size Is Too Small. Most Aftermarket Drain Fittings Have too Small of an Inside Diameter Which is Often the Problem. A Factory MHI Drain is 16mm Inside Diameter. Aftermarket -10 an Drain Fittings are 12mm Inside Diameter. This Causes the Oil to not Drain Effieciently and the OIl backs up in the cartridge. With new oil filling the Cartridge and the Old oil not being removed, the oil pressure builds up in the cartridge and is forced out the seals.
2. Blocking Crank Case Ventilation Causes the Pressure in the oil Pan to Build up, Which no Longer Allows the Oil to Drain From the Turbo Properly, Because the Crank Case is Pressurized.
3. Oil Level. The OIl Level Can Be Higher Than the Oil Seals, if You Put too Much Oil in the Oil Pan, or If the Turbocharger is Sitting to Low in Relation to the OIl Level. Both Situations can Cause oil to Lean Past the Seals.
4. Oil Pressure.  The Oil Pressure Being Too Low, will Cause The Turbo To Wear the Internal Parts of the Turbo. Usually Once the turbo develops some In and Out Shaft play the Seals get Worn out in the Process, Which makes the Turbo Need a Rebuild.  The Oil Pressure Being Too High, is Never the a Problem Unless The Oil Drain is Not Large Enough To Remove the Volume That is Being Fed into The Turbocharger. Ball Bearing Turbos Need a .035” Restrictor However, Because their Cartridges Are Much Smaller, and They Can only Hold So Much Volume.
5. Oil Restrictor in a Journal Bearing Turbo. Having and Oil Restrictor in a Journal Bearing Turbo can Causes Turbos to Eventually to Blow oil, Because it Starves the Turbo Of Oil, Which Causes the Internals of the Turbo to Wear out (including the Seals). Don’t Use a Restrictor with a Journal Bearing Turbo, if You think the OIl pressure is “Too High” Then a Drain with a Larger Inside Diameter.
6. Hot Shut Offs.  After You Drive Your Turbocharged Vehicle Hard, You Should let the Engine idle for 1 to 2 Minutes to Allow The Oil to Circulate Through the Turbocharger to Remove the Heat from the Internal Parts of the Turbo. If You Do Not Do this, Then the Next Time You Start the Vehicle up, The Turbo Internals Could Be Dry, Which can Cause the Internal Parts the Wear Out Prematurely.
7. Improper Oil Weight.  Just like Engines, Turbochargers have a Required Thickness of Oil to be Used. If you Use too Thin of oil Weight For the Ambient Temperatures, Your Turbo can Result in Blowing Oil. The Minimum Weight Required is 10w 30, But Often Some People Are Able to Run 5W Oil in Their Cars in Below 0 Degree Temperatures, but just Remember Your taking a Risk if You Forget to change the OIl When Warmer Temperatures Come Around, Your Turbo Will Fail Quickly!
8. Oil Contamination Oil Contamination Will Destroy a Turbo Quickly. The Foreign Material, can be Debris from a Previous Blown Engine, sand blast media, leftover rtv gasket maker, or Anything that Could have Fallen into the Oil Pan. This Is the Worst Case to Have, Because it Often requires the Engine to Be Rebuilt and Flushed Thoroughly.  These Particles can Be Trapped in the OIl Journals, Which Never Allows The Debris to Leave No Matter How Much You Change the Engine Oil. Often If these Particles Make it to the Turbocharger, the Bearing Housing Gets Scared and Causes the Cartridge to often Need Replacing. Luckily Now We offer New Cartridges for Turbochargers!

Here Is My Experience With Running Restrictors on Holset Turbos:

“I built 2 Holset HX40 Turbos With Oil Retrictors in the Passed, They Both Failed Really Quickly, I Used a 5/64 Drill Bit Which is .075” Approx Which is What People Recommend Online, Both Failed and I had to Warrantee Them. The Reason Why People Started to Recommend Using Oil Restrictors in the First Place is Because the Oil was not Draining Effectively Enough From the Turbo in Some Shape or Form. The restrictor Helps Prevent the Excessive Oil Volume, But it Often Can Restrict too Much Oil Which Causes the Turbo to Fail.”

The Same Rule Goes for Garrett, PTE, Turbonetics, and Comp Journal Bearing Turbochargers… Dont use a Restrictor, use a Larger Oil Drain with the Proper Inside Diameter(16mm)!

Keep it simple:

• Run the oil feed from the oil filter housing
• Large enough oil drain (16mm ID)
• Properly vent your crankcase
• Run the appropriate oil thickness

Under the Circumstances Where the Turbo Is Leaking Oil, You are also Losing Oil Pressure. It is Very Common for the Engine to Spin Bearings, or lose Compression Due To Lack of Oil Pressure in the Engine, Due to Your Turbo Leaking all the Oil pressure out the Turbo Seals. The Main Reason is Because The Oil pan Runs Dry and The oil Pressure is Lowered When an Oil Leak is Present. Park the Car and Fix the Turbo Before You Create More Problems!