I'm approaching my first oil change on my 03 Mitsubishi Outlander @ 6000kms (2.4L 4-cylinder w/AWD). This is abiding by the Mitsubishi "severe" service for Canada. I have the following oils on hand: 1. Castrol GTX 5W30 2. Motomaster F1 Dino 10W30 Or, should I buy some synthetic? Mitsu recommends 5W30 year round, but it is going to get hot in this part of Ontario real soon. Any ideas?