Fellow mu-X owner here! If you're thinking about upgrading from the standard Isuzu Genuine Motor Oil 10W-30, check out the ZIC X7 Diesel 10W-30 Fully synthetic. I used Amsoil Turbo Truck 5w40 too (10k km interval) but it's expensive for my Garage queen mux haha. Mobil Delvac1 5W-40 is good as well.
My mom's impreza will loose oil between oil changes with 0w-20 and will be fine with 5w-30. It burns the thinner oil.
My wife\u2019s 2012 Impreza is at 195k miles and I switched it to 0w-30 and then 5w-30 due to oil consumption. Was burning a quart every 1K miles on 0w-20, burns half that on 5w-30. I\u2019m actually considering going thicker.
The dealership here itself was using 5w-30 as the default for oil changes even though 0w-20 is stamped on the filler cap. After checking myself that Subaru said that would be OK, I started using it too for my own changes just to avoid flipping back and forth -- though I have no idea if that would be a problem. In any case, the Forester seems happy, even if the mileage may have dipped slightly.
Engine does become a bit quieter with 5w-30.
I have Signature in my 25. Smoothed out the engine noises quite a bit.
Engine noise is a little, well noisy, mine is less rumbly/vibrationy after I changed my oil and used Amsoil Hybrid oil. I can’t generally feel anything when the engine kicks on now, before I could definitely feel it every time it kicked on.
I switched oil to AMSOIL signature series synthetic, from everything I read, it out performs other oils, used to use Mobil 1
My biggest regret, not swapping out the shitty 0w-20 factory filled oil for some 5w-30 Amsoil, Motul, or Pennzoil Ultra platinum the moment I took it home. Don\u2019t wait till 1k miles.
Get a catch can but that mobile 1 oil you are using is for shit . Amsoil is best for mustangs and the best for that matter period it\u2019s cost but you can run it 25k
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If choosing engine oil across many manufacturers, check the part ranking. If your choice is down to two brands, the PartReview part comparisons help.
We compare engine oil across these categories:
In March 2026 on PartReview, engine oil AMSOIL were overall better than OEM Subaru.
In March 2026 on PartReview, engine oil AMSOIL were overall more popular than OEM Subaru.
By vote balance, engine oil AMSOIL surpassed OEM Subaru:
By number of reviews, engine oil AMSOIL surpassed OEM Subaru:
In March 2026, according to PartReview, these manufacturers led the same number of car-specific ratings:
AMSOIL are chosen by owners of cars such as: Honda S2000, Toyota 4runner, and others.
OEM Subaru are chosen by owners of cars such as: Subaru Forester, Subaru Impreza, and others.
If this comparison didn’t fully answer your question, there are many others on PartReview.
For example, comparisons of engine oil AMSOIL with: Mobil, Castrol, LIQUI MOLY, MOTUL, Shell, VALVOLINE, PENNZOIL, RED LINE, OEM Toyota, Mannol.
Also available: comparisons of engine oil OEM Subaru with: Mobil, Castrol, LIQUI MOLY, MOTUL, Shell, VALVOLINE, PENNZOIL, RED LINE, OEM Toyota, Mannol.
You can also see who is better among other engine oil manufacturers: Mobil or Castrol, Mobil or LIQUI MOLY, Mobil or MOTUL, Mobil or Shell, LIQUI MOLY or Castrol.
