My 04 WRX has 17,000 miles on it (running stage 2) and I change the oil every 2500-3000 miles. I use Mobil 1 5W-30 with Subaru oil filters. When I drain the oil, I get as much as possible out and put everything back together (I am a neat freak) perfectly. So I use a 5Qt bottle to fill up my car but leave just a little at the bottom. I am trying to get as close to 4.6-4.8Qt in the car.
Here is where it gets strange. I put the car down and let it settle, then check the oil before I do anything and always check for leaks. Around the magical 250-300 miles mark 1Qt will dissappear. The oil mark on the stick is at the bottom hole so I put in 1Qt and the mark stays at the full mark right up until I change the oil again. I don't know where the oil is going but it happens everytime. Has anyone had any experience with this? I have an extra 5Qt bottle that I use to top off the 1 Qt everytime and it is 1 Qt EXACTLY. Where is it going? No leaks, nothing in the engine bay, no smoke from exhaust, no buring oil smell.