Subaru Technical Support Bulletin (TSB) 02-97-05 included at the bottom of this page

Unexplained "oil starvation" problems are a nightmare for enthusiasts with expensive high performance aftermarket turbochargers. The last thing anybody wants to hear when their turbo is inspected is that their turbo died due to lack of oil pressure or volume.

But as sure as you are that your engine runs fine and has perfect oil pressure, some guy at the turbo shop where it was produced is even more certain that the turbo bearings burned up due to a lack of sufficient lubrication. Who is correct here?  Actually both can be.  It IS possible for the engine to be OK, and have no damage but the turbo to be completely ruined; we have figured it out, and so has Subaru.  They have even issued a series of Technical Service Bulletins (TSB's) that explain how it happens and what to do about it.

As it turns out, there is an oil filter screen built into the factory oil feed banjo bolt at the cylinder head, and Subaru wants it either serviced regularly or removed completely in order to avoid turbocharger oil starvation and failure. Insiders we have spoken with told us of numerous and recurring turbocharger failures even on completely stock 2.5 WRX, STi, Forrester and Baja vehicles due to this problem, prompting an Official Subaru Service Bulletin in October 2007. In one reported case in Alabama, even a low mileage 05 Baja which had all its regular 3k mile oil changes at the dealership experienced a stock turbocharger failure due to this oil filter becoming plugged with sludge.

This turbo screen is not to be confused with the screen that filters the oil for the AVCS valve which does not affect turbo oil supply since it is after the "tee" that splits off the oil supply line to the turbo. The AVCS filter can also become plugged and affect the performance of the AVCS solenoid, but luckily when the AVCS filter becomes clogged there is no catastrophic failure of a $1000+ component as in the case of the turbocharger filter, just a check engine light due to the non functioning AVCS.

The turbocharger filter can be seen in the diagram below, it is marked "A"

Most drivers are not aware that they even have a turbo oil filter in their oil supply line; much less that it requires periodic cleaning with each oil change. The following is from the Service Bulletin titled "Turbocharger Oil Supply Mesh Screen #02-103-07";

"the mesh screen which is located inside the banjo bolt that secures the turbo¬charger oil supply pipe to the back of the right side cylinder head should be checked to make sure it is not clogged or restricted especially if the condition of the oil is questionable or as to when the last oil change was performed. If clogged or restricted, it will reduce or cut off the oil supply to the turbo resulting in failure. The oil supply pipe should also be checked to make sure that there are no obstructions."

Also stated in the bulletin is that this is even more critical that this filter be checked frequently when the car is "used under severe driving conditions, such as moderate to hard acceleration and engine braking on a somewhat regular basis".  Any vehicle with upgraded turbocharger is most assuredly going to fall into this category.

For some time we had scratched our heads about the reason that a "perfectly running car with no engine issues" could kill a turbocharger that was installed and broken in correctly.  There is finally official documentation from Subaru of this problem to support the observations that the oil supply to the turbocharger can become cut off or restricted without any damage to other parts of the engine.

We recommends REMOVING this "Turbocharger Oil Supply Mesh Screen" in all vehicles running ANY upgraded turbochargers, whether ours, or other manufacturers. The thrust bearing and oiling system in our turbochargers has very little tolerance for reduced or limited oil supply. In fact our thrust bearing and oiling system requires almost TWICE the oil volume as a small stock IHI turbocharger and although "stock" components can be OK with slightly restricted oil supply, higher performance, tighter tolerance units simply cannot withstand their oil supply being restricted. This is why it is completely possible that a slightly restricted filter will destroy your Zilla or SuperZilla or other upgraded model, but not destroy your stock turbo when installed back onto the car after the failure of the aftermarket unit.  This made it not only hard in the beginning to figure this problem out, but also caused some "ill will" for customers when stock turbos were installed after a failed aftermarket unit and the stock replacement didn't immediately fail.

With this problem now fully documented and explained, we hope to reduce the number of customers (both ours and other company's) who destroy their turbos from lack of proper lubrication. At the very least we are trying to advise anyone that might read this page on how to avoid a potentially expensive problem. This is a Subaru "Warranty Item" it affects the operation of the AVCS valve and stock turbo. From our experience, this DOES NOT CARRY OVER to aftermarket turbochargers. 

It is every car owner’s responsibility to check and verify that this turbo filter is either removed for aftermarket turbos, or perfectly clean for replacement with a stock unit at all times. Do not assume that since you had a "Professional Shop" or "Tuner" install your turbo that your filter has been removed or checked, most people do not even know that the filter exists!  At the time of writing this, we have 4 turbos installed by VERY professional shops in our facility now with oil starvation damage. 

Also, do not assume that since your turbo has not failed that you are immune to this problem, you are not!!!  You might still have the filter, and have been lucky that it has not restricted oil supply "YET".