READ BEFORE YOU POST!
I first created this thread after experiencing a couple back to back rod-bearing failures due to some bad shop advice and work so I wanted to learn more about the problem to prevent future issues. The thread ended up taking off and has largely become the primary thread about this well-known and unfortunately 'notorious' Subaru issue.
This thread has been going for several years and through many expert contributors commenting and sharing we have lots of great information to help Turbo Subaru owners understand this issue. The thread is extremely long so in an effort to prevent some of the same questions being asked over and over I've made a synopsis for new visitors to read and/or be pointed to to catch them up on the main themes detailed out in the thread.
I will come back and make changes to this initial post sharing sources and quick links to discussions as time allows to further bolster this initial post. Some of the explanations are just high-level conceptual overviews meant for quick reading and aren't 100% accurate as a result.
Hopefully this synopsis will help future visitors understand the range of topics discussed in the thread without having to read the whole thing.
I feel strongly that the biggest contributor to these failures is the increased popularity and increased sales in general but also the increased rates in which these cars are modified. The WRX and STI are likely the highest-volume "Tuner" car besides the Mustang and perhaps the most likely vehicle to have power modifications to the engine both in hardware and ECU flashes. They've become extremely prolific and as a forced-induction engine are very effective in pulling more power out of the stock engine setup.
Regardless of modifications and tuning, these cars are driven hard by an enthusiastic community who push these cars to redline quite frequently and there are some 'weak points' from the factory that have made for some failure issues to come up both stock and modified as a result:
For CAFE reasons, Subaru began recommending Resource Conserving 5w-30 oil in their turbo models around 2008 or so even though they didn't change the engine itself or cooling system to help the 'weaker' oil deal with the harsh conditions these engines often see in being driven hard or being lightly modded.
The manual used
to clearly state that harsh driving conditions warranted a temporary fill of heavier weight oil and a lower oil change interval for Turbo Models through approximately 2006-2007. Subaru eventually removed those recommendations roughly around 2008 or so which surely has contributed to the number of Turbo Subaru drivers sticking with the inferior factory oil fill and elongated oil change intervals even after tracking their car, installing aftermarket tunes or simply driving around full throttle on a regular basis as so many trubo subaru drivers do.
There have been many reported cases where Subaru owners have been hassled, pushed and otherwise threatened to have their warranties voided if they didn't use the oil specified in the manual. Even in some cases the dealerships required the owner to have all of their oil changes performed at the dealership or have detailed receipts of the type of oil and the date and mileage of the oil change kept to honor any warranty claim. Unfortunately this is not legal and also bad advice as the dealerships do not understand that the oil being recommended is to achieve the best possible EPA numbers and doesn't provide the maximum protection for the engine under harsh driving conditions.
Over the years for the same CAFE/EPA pressures, Subaru has slowly changed the factory tune logic to also meet increasing fuel economy and emissions standards that leaves a little less safety margin for reducing knock when under harsh driving or using lower quality/octane fuel that is often attributed to some of the apparent increased failure rates since 2006. Increased Ring Land Failures also increased in this time period for the same reasons. These changes began in the later years of the GC chassis (reaching a peak in 07 through 09) but have been found to continue through even the current generation STI.
The main issue with the tune is the changeover from Closed-Loop to Open-Loop fueling has continually been delayed later in the RPM band and further into the throttle input range. In "Closed Loop" the ECU targets a specific air-fuel ratio - in this case STOIC which is the cleanest and most efficient fuel ratio but also the most lively and prone to knock.
**Closed Loop uses the O2 sensor to constantly check the exhaust stream to measure the effective Air-Fuel ratio and then applies learned and pre-determined corrections to the injectors to keep the fuel mixture on target.
**Open Loop is where the engine ignores sensor feedback and instead applies a set amount of fuel based on calculated intake volume, load, rpm, throttle %, boost levels etc. It's up to the accuracy of the tune to ensure that the targeted fuel ratios are met because the ECU does not apply automated changes to the fuel system to compensate for errors during Open Loop. From the factory, Open Loop fueling tables are typically quite safe for the engine but are being utilized less and less as more driving conditions are being addressed by a Closed Loop fueling strategy. Closed Loop is great for more advanced Direct Injection engines where the fuel can be controlled much more accurately without delay but for Port Injected engines can be a bit of an inexact science regardless of sensor accuracy or processing power.
2: Knock Correction:
Furthermore, some changes have been documented to the knock correction logic where the engines are allowing larger knock events before retarding timing or changing fueling conditions again in an effort to maximize fuel efficiency at the expense of more potential engine wear. The EJ series engine had not changed mechanically very much to deal with the higher potential stresses since 2004 in general and in some cases, issues with build quality and component quality have been found as production numbers increased.
There have both been production runs where faulty engine bearings and engine rings have been suspected to be used as well as runs where Subaru admittedly found defects and issued service bulletins (need to find more info to cite on this). Many engine builders have also found production runs where the tolerance range for Rod Bearing Clearances seemed to widen from the well-known .0014''-.0018'' to .0012''-.0018'' (citation also needed, Maxwell Power in this thread detailed out this scenario) which is independent of material defect but contributes to oiling issues under high-stress that can lead to failure.
While the mechanical issues appear to have been largely addressed starting towards the end of the GR model run (2012-2014 on) there are still many cars affected that are experiencing failures from what it seems.
There have also been many recorded instanced where the Oil Pickup Tube has failed causing oil starvation to the engine. Popular aftermarket mods for rebuilt/built engines is a better pickup tube like a Killer-B which is a popular affordable brand.
Earlier EJ257 engines used a smaller 10mm oil pump but Subaru began using a 11mm oil pump in 2008. The actual reason for this increase is unknown but most likely is due to the addition of dual-avcs engines where a little more load on the oil system would be present from 2 more oil pressure actuated cam gears. Many engine builders use the larger 11mm pump even on single AVCS engines with the idea that better oil pressure can be sustained at higher RPM's. Opinions are mixed on whether larger oil pumps improve or exacerbate the issue at all but Rod Bearing failures are mostly an oil-related issue. Fear that too large an oil pump can cause more failures is due to over-pressurizing the oil and causing cavitation - bubbles from pressure and heat in a fluid.
Crankshaft Coatings: Subaru has gone through several renditions of crankshaft surface treatments that have limited data on how they truly impact bearing failure rates. Nitride Coated Crankshafts were used initially to replace the traditionally Polished Crankshafts and then later replaced by a Heat Treated Crankshafts from the factory (details and citation forthcoming). These treatments/coatings are intended to harden the crankshaft surface to prevent marring and scoring from metal to metal contact with the bearing surfaces. The only conclusive recommendation is that proper oil and bearing clearances are far more important than crankshaft coatings although many engine builders find that fresh treated crankshafts are more desierable in their builds.
- Ignore the manual and use a non resource-conserving _W-40 oil
There are 0w-40, 5w-40 and 10w-40 oils well documented in this thread that perform very well in turbo Subaru engines. The most commonly found and popular oils are: Shell Rotella T6 5w-40, Mobile 1 Advanced Full Synthetic 0w-40 (DO NOT USE REGULAR OR GREEN CAP MOBILE 1), Pennzoil Ultra 0W-40 just to name a few with good data. The first number matters less than the 2nd number but if in doubt about trying an oil go for a thicker W weight like 10w-40 if you can't find the named oils above.
- Taking extra precaution to use fresh high-octane fuel
- Increasing oil change intervals in general but especially when driven hard.
- Avoiding prolonged runs at or near redline and WOT. If you drive heavy, change your oil more frequently and use better oil!!
- Avoiding out of the box staged tunes when you're unable to verify the 'health' of the tune via datalogging & wherewithal to make corrective changes
- Not installing aftermarket intake components without a proper tune as the accuracy of the MAF sensor's readings can be affected causing improper fuel ratios
- drive it like you bought it. These cars are fun but they are essentially CHEAP fun so don't expect them to pull racetrack duty out of the box like a supercar.