gathermewool
Site Donor 2023
'14 FXT
Currently: ~5k miles
OCI: 7.5k miles
Spec: 5W-30 synthetic (no special certs.)
OC History: Changed the factory fill at ~4k miles with mix of Rotella T6 and Mag1 5W-40 (from stash.) Factory filter remains installed (Tokyo Roki filter, known for durability - I've cut a few open and they're much better-constructed than the Honeywell replacements.) Plan is to change oil and filter again at 7.5k.
Driving Style/Commute: Most days I drive 16 miles to work and then 16 miles back home, only stopping for errands a few times each week. It is very rare that the oil temp does not exceed 170F during each drive, and usually gets up to >180F, even during this very cold winter.
I usually drive off very soon after starting, and drive very gently on 30 MPH roads for the first half of my commute on the way to work and the first few miles of my commute from work (the blue cold coolant temperature indicator resets at 122F, and is usually off before I need accelerate up to highway speeds.
With the twin-scroll turbo this engine is at positive pressure frequently, and at 9+ PSIG (of ~15# max) at least twice per day while accelerating onto the highway or passing someone. Every so often, I'll feel a little froggy and drive agressively, reaching max boost and WOT frequently, for miles on end.
’08 Civic:
Currently: 98k miles (Purchased @ 60k miles)
OCI: Per Maintenance Minder: @ -100 miles on the MM (below 0%)
Spec: 5W-30 (No special certs)
OC History: Maintenance documents from PO show all oil changes per the MM. I’ve followed suit until just this oil change. I’ve been busy with work (shift work and travel,) and when I do have free time I don’t want to waste it in the hobby shop changing the oil. Because of this, I’ve been using Castrol Edge w/ Ti 0W-20 to give a safety margin for instances like now, giving me time to change my oil when it’s more convenient for me.
Driving Style/Commute: Grandmotherly. My wife drives this car, and it’s rare that she gets it above 3.5k RPM. I drive it every so often, and usually ring the little R18 out to >5k RPM getting on the highway, but also drive it pretty gently to get as high MPG as possible.
For the purposes of this thread, she has the same commute as described above for the ’14 FXT.
Question:I have a stash of 3-4 OCI’s worth of German Castrol 0W-30 API-SL rated oil, and 2 quarts of Rotella T6 left from my STI. I’m debating whether to use this oil in my Civic, since it doesn’t seem to care which oil I use in it, though I’m apprehensive about using the heavy GC and heavier T6 in it.
I can use my stash up in my FXT, but I’m wondering whether it makes sense to risk angering the warranty gods (the current sump filled with Mag1/T6 will be changed before the first Subaru-required OCI, so I’m not worried about this; I’m also no worried about an oil-related failure with either T6/GC) and I’m curious as to whether a low volatility oil like the new Pennzoil GTL selection might make more sense long-term, even though they’re Resource Conserving. In the end, I care more about choosing the right oil for my application than
So, what do you guys think? I’ve already considered running the severe service interval of 3,750 miles, using an approved “5W-30 synthetic” every 7,500 miles and something like GC/T6 at the halfway point, but that seems wasteful with the oils I’m considering using. Outside of the advice given here, I do plan to send out the FF for analysis, and then whichever oil I choose to use long-term after another few intervals.
I don't know what I would do. Maybe use the GC in the Civic and the mix the RT6 with some PP 5W-30 for the FXT? 
I'm impressed with the M1 ESP 5W-30 WRX uoa that was just posted. That doesn't help your stash problem though.
-Dennis