Originally Posted By: Padawan
Subaru is particularly lax in its recommendations/requirements regarding oil for these engines.
If you consult the manual, you'll note that it specifies an SJ or SH (or even SG) oil with a "preferred" viscosity of 5W-30 up to approximately 105 degrees F ambient temperature. I strongly assume this "preference" is primarily related to fuel economy concerns, and the manual goes on to recommend 10W-30 or 10W-40 for any ambient temperatures above approximately -5 degrees F.
To make things even more interesting, there is also a statement that, "If the vehicle is used in desert areas, in areas with very high temperatures, or used for heavy-duty applications such as a towing a trailer, use of oil with the following grade and viscosities is recommended: SJ or SH 30, 40, 10W-50, 20W-40, 20W-50." Yes, that's a straight 30 or 40 weight oil included in the recommendations.
It's interesting that you posted this in the HDEO forum, because HDEO is what I use exclusively in my 2006 Saab 9-2x (rebadged WRX) and my fiancee's 2001 Forester.
We live in northern NJ, and while it's certainly not a "desert area", it's relatively mountainous and we do a fair bit of stop-and-go driving as well as ascending and descending the aforementioned mountain grades on our daily commutes - enough so for me to personally consider ours "heavy-duty applications." In the summer, I use conventional 15W-40 HDEO (Rotella T this season) and switch to a 5W-40 such as Rotella T6 or DELO 400 LE in the winter. Since we put a decent amount of miles on our cars, I'll probably do an "autumn" change with Rotella T5 10W-30 as well before we actually hit the cold months.
My primary point in this lengthy anecdote is that A.) these Subaru engines are not at all particular about what oil they use (although I feel that they prefer something more viscous than the "recommended" 5W-30), and B.) There is no harm whatsoever in switching from synthetic to conventional or anywhere in between.
Thanks for the comprehensive info from a real world user. I believe I am leaning towards a conventional switchover, but not sure yet which one. Rotella or Delo sounds like a great idea since I use Delo in my truck. I might as well just keep to one oil and call it good, right? I am really glad to hear that the engines are easy on oil. I have also seen, from crawling around underneath, that these are extremely easy to work on. Even more of a bonus since I do most of my own stuff!