I seem to have been summoned.
Yea, customer has a 2009 WRX with a Perrin AOS installed on it, otherwise, fairly stock engine. (K&N intake, COBB AP running Stage 1 tune, dress up stuff, that's about it). He grenaded the engine during the cold snap we had while doing about 125km/h on highway 2. Engine let go really quick too, within 30 seconds of first sign of trouble. Ended up spinning a rod bearing on cylinder one due to oil starvation (closest to the oil pump, so makes sense). We figured it may have been an issue with low oil level as we only drained about 1.5L out of the pan.
Customer did have a Perrin AOS installed on the engine. When we pulled off the feed line for the breather hoses, oil gushed out like crazy. We drained probably close to a 1/4L out of the drain hoses alone. When we pulled the intercooler off, it was filled to the brim with oil as well. We've drained it three times so far and got about 1L of oil out of it. Found oil in the turbo inlet hose, intercooler to throttle body hose, and some in the intake manifold as well. We know that when the block let go, it did spray a ton of oil out, but not 2.5L worth. Checking the exhaust, it was completely coated with oil too. Customer complained just before the engine let go that he did notice a lot of smoke coming from the exhaust, but couldn't tell if it was smoke or fumes from being -35 degrees outside when it let go.
When we pulled off the AOS, we drained 150-200ml of water out of it, and the drain line from the AOS to the block was dripping brown sludgy water (looked like it was dripping a double double out). Turns out what had happened with his AOS was that 1. the drain line was pinched due to how it installs on the block and lack of clearance around the EGR system on the block, 2. the drain line most likely froze as it was getting a ton of cold air rushing over it in it's original routing from the air being directed down onto the intercooler, and 3. in the Perrin AOS, they install a foam filter, which they recommend to remove for vehicles in climates that reach temperatures below freezing. The customer didn't remove this when he installed the AOS himself. The foam must've frozen with all the condensation build up in the AOS from it sitting right above the turbo, the coolant running through it (Perrin one's have a heater element in the base of it to help separate the vapours from the liquid oil), and all the really cold air in the engine bay, causing it not to drain. If there is no free flowing drain for the system, the AOS is then placed under a full vacuum, which would cause the feed lines off the valve covers and original PCV location to start to cavitate and get sucked into the AOS and then fed back to the turbo inlet and straight into the rest of the engine's intake system.
Being 1.5-2L down at minimum would've caused cylinder 1 to have all of it's oil sucked away from it (again, closest cylinder to the oil pump), which resulted in oil starvation on cylinder 1 rod bearing, which resulted in the bearing spinning, seizing, causing the rod to snap into 3 pieces, piston making contact with the head, and one of the pieces jamming into the block and punching a hole through the top.
So, Coles notes version, in really cold temps, AOS froze up, couldn't drain, created a vacuum in the system, started sucking oil out of engine, caused oil starvation on cylinder 1, engine goes boom and has big hole in it.
I have photos of all of this too if needed, just don't really want to host them.
I'd say avoid AOS unless you have reason to really need one due to having an engine with forged internals that will have looser tolerances upon start up. If you're concerned with oiling issues, best thing to do is check it every time you fill up and top up as needed. We're printing a sticker for the customer to put on his fuel cap that just says "CHECK OIL" so he's reminded every time he fills up.
