Switching to synthetic on a higher mileage engine can sometimes cause a leak. Try it once to see if you have any.
The 2.5 does have some oiling issues, so as stated, go with 6 to 6 1/4 qts.
Mobil 1 is the best 'department store' oil. Amsoil, redline royal purple etc are very good oils, but can be pricey.
