I have a 2006 skidoo skandic 550F and I have been using Castrol 2T snowmobile oil in it. I wanted to get everyone's opinion on if I should stick with it or switch to another injection oil, I operate generally in colder weather. The person I purchased it from ran mineral oil in it. It seemed to do pretty well this year but I didn't test it to much. not sure if its related but I get horrible gas mileage in the skandic, and change plugs probably every 500 miles. Also if I was to change oil would I need to drain the tank or could I just start adding the new oil to it?