Switch from M1 to Shell Rotella T Synthetic

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Mar 10, 2006
Carlsbad, CA
I need your opinions. I am thinking of switching from M1 5w-30 to Rotella T Syn 5W-40. Hoping the motor will quiet down and that Rotella actually is better on the wear side of things. My OCI is 5K miles.

Is this oil too heavy for my 2004 Subaru Outback 4 cylinder, which recommends 5W-30?

I live in San Diego.

Appreciate any input.

Personally, I'd first step up to a "thicker" 30-weight oil such as German Castrol Syntec 0W-30 before jumping up to the even thicker Rotella T 5W-40. Granted, GC is more expensive than the Rotella, but it's usually available for the same price (or less) than the M1 you're using now. GC gets my vote (in fact it's what I run in my '05 Subaru Impreza WRX STi which pushes out 300 hp from it's turbo-charged 2.5L flat-4).
I agree with AndyH. Rotella, despite it being 5w, is pretty thick stuff! I think you'd take a noticeable hit in fuel economy and engine "peppiness".
Drop down to a Group III like Castrol, Pennzoil or Valvoline to quiet things up. Change at 7K or if Suabru demands - then less mileage. For San Diego climate, you could easily go with 10W-30 too.
It's 40 weight, not molasses.
I would prefer to stick with a synthetic, perhaps a hydrocraced one! Is there one that you guys is at least as good as M1 but perhaps quieter.

Maybe Subs are simply noisy?
brucelee: All the oils mentioned in this thread are synthetic oils. GC is easily as good as Mobil 1 (if not better) and many folks have commented on it's tendency to quiet down their engine (to some degree). I say it's worth a try.
I have had 3 subies and have M1 5W30 in my Forestor right now. I do not note any increased noise. Subies do not sound like an inline 4, they have there own sound.

I would make my decision based on a UAO, not a percieved noise problem. Sadly, I cannot post a UAO on my Forestor with 5W30 yet.
I think Subaru engines are noisey. All four that I've had are noisey. They also have a reputation for being noisey for nearly 1/4 million miles before haveing to be rebuilt. With the exception of a seal or gasket problem every once in a while throughout the various model years. If you notice, they also shake the front of the car at startup...because the pistons are going side-to side instead of up and down. My four-year old noticed that the first time she was in one when it started up. After a while, especially if you don't drive other cars, the Subaru noise gets to be "normal".
Based on many UOA's posted here, M1 0W-40 has a tendency to shear down to a 30-weight in the first say 4,000 miles. It then will thicken back up to a 40-weight over a longer OCI. In my opinion, this is less than ideal. I have some M1 0W-40 in my oil stash too...I suspect it will sit there for quite some time as I think the GC is the better option between the two oils.
a buddy of mine has a WRX (pushing out over 275 hp) that was pretty noisey. He switched from Mobil 1 5w-30 to PP 5w-30 and noticed a pretty large reduction in noise.
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