Originally Posted by rao
I apologize; I got 2 messages mixed up.
There is a school of thought that you can't change back once you use synthetic oil, there is another school of thought that it doesn't matter. There is some merit to the idea that you shouldn't change to synthetic on a motor that has a lot of miles on it (like over 85k) because it might cause leaks due to changes in the seals. The key is to use oil that is properly rated and to change it at the right intervals, don't get hung up on the brand.
I am actually in the midst of trying to make a decision on whether to switch to synthetic or not. My previous car was an 1997 Audi A4 1.8T Q and was told to use synthetic because Audi/VW won't warranty turbos that didn't have synthetic oil in the engine.
Now, Subaru is not saying anything about synthetic for turbo, etc. The service manager at local dealer says older mileage cars can convert to synthetic, which is contrary to the leakage theory you mentioned.
I've also been told that once you switch you shouldn't keep going back and forth...I'm so confused. Can anyone provide some objective, more data driven information on this topic?