I racked up just shy of 10,000 miles since my last oil change over 6 months ago, which meant it was time to do it all over again. The timing worked out perfectly to allow me to change all of my fluids before the weather got cold enough to make it an annoying task. For those who haven’t been following along with my previous oil change posts, I use AMSOIL fluids in the engine, transmission, and differential. I also follow a modified service interval. For the transmission and differential, Subaru suggests a 30,000 mile oil change interval, but I dropped that to 20,000 because of my severe use, and because I think AMSOIL fluids are a bit thinner than the OEM fluid. The transmission and differential fluids looked fine when I changed them (though I assume the transmission fluid was changed when I had the throwout bearing replaced recently). Also, there were no more metal shavings on the magnetic drain plug for the differential than one might expect after 20,000 miles. So no issues there.

Subaru dictates a 6,000 mile oil change interval for the engine, but AMSOIL claims 25,000 miles, or 15,000 under “severe use.” Since I fall well within the severe use category, and didn’t want to push my luck, I’m doing 10,000 mile intervals, which is still significantly higher than what Subaru suggests. I’m also sending samples at each oil change to Blackstone Labs for analysis. Before we get to those results, though, let’s consider the past 10,000 miles:

  • Twelve autocross events.
  • Towing a 650 lb trailer to-and-from these events (and more, such as to TireRack and back for winter tires).
  • Road trip to NJ.
  • Mostly stop-and-go city driving the rest of the time.

Oh, and most importantly (and perhaps most surprisingly for people familiar with boxer engines), I did not add a DROP of oil to the engine in those 10,000 miles. At the time of this oil change, the oil level was less than 1/2″ from the full mark on the dipstick. So that’s a good sign… but an even better sign comes from the test results, as you can see from their comments:

“It looks to us like this BRZ has reached a pretty stable level of operation, with good wear metal readings showing a healthy engine. Universal averages are for an oil run of about 5,500 miles, and metals on your longer run are in good shape; no worries from what we can see. Note that copper is finally done washing out from initial wear-in, and is now about half what the average FA20 engine produces – great bronze wear! The oil was in good shape, with no contamination and strong TBN. How do you feel about a 12k interval? This engine’s ready for it.”

Many of my numbers are significantly lower than the standard results for much shorter oil change intervals. Of course, that’s not to say my engine won’t explode tomorrow, but these test results keep getting more and more promising. I’m really hoping that this turns out to be a good, happy, reliable engine. They want me to try increasing my oil change interval, and judging by these results, it probably wouldn’t hurt anything, but I think 10,000 is good enough – not to mention that it aligns well with my transmission and differential fluid changes. I will, of course, continue to change my oil filter twice as frequently (every 5k.)