I recently bought a 2010 Impreza 2.5.  The manual calls for 4.2 qts. of oil for a change.  However, that amount shows halfway between low and full on the dipstick.  Is the manual wrong, or the stick; should I fill closer to the full mark of leave it be? Thanks.

As long as its between the marks its fine. These do tend to use about 1/2 quart between changes, so if you want to fill it to the full mark it will ensure the level is sufficient until the next change without having to add. Just don't overfill it.

That said, be sure to check the level at least every two weeks. It's best to check in the morning before starting.

I work in an oil shop, and for my 98 forester (ej25d) it calls for 4.2 qts w/filter. This brings the level halfway up the safe margin. Anywhere between the 2 dots is acceptable as long as it is not low. It takes 4.5 qts to bring it up to the top. IF your car consumes oil, top it off; otherwise, in the middle is acceptable.

 

Interesting fact, the 2.5 calls for 5w30 oil, but the 2.2 (01 impreza) calls for 10w30 according to my catalog at the oil shop. I you read the owners manual, it may state (as it does for the 98 forester) that "5w-30 is not recommended for prolonged high speed operation)