From my experience 4 months is not a real long time to be too concerned about starting up your XF. I think you battery will be your biggest problem depending how old it is and what charge it had on it when you left. Sounds like you did the proper things before you left. Burn up the old fuel and enjoy being back in the greatest country in the world. I served in the Navy and was gone for longer periods (9 months to 14 months)and it always felt soooo goood to be back in the U.S.A again. Welcome home and thanks for serving. Go out and find a fun road to drive your SRT on! p.s. check you tires air pressure too.