Hi, I drive a 2006 Civic and use 87 regular gasoline in it. I accidentally put 4 gallons of 89 grade instead of 87 in it today. Now, the 89 is an equal mix of 87 and 91. That meant I put 2 gallons of the correct grade, which is 87, and two gallons of the wrong but higher grade, which is 91. Would that hurt the engine or impact the car's current or future performance? Will the higher grade eventually burn off completely without leaving deposits or causing any damage to the engine? Thanks a lot in advance.