I was wondering if there was anyone that can answer why my engine is running rough after an oil change. I used Valvoline 5W-30 Full Synthetic, only putting 4 1/2 qts in the engine and using a 1/2 qt of Marvel Mystery Oil. I am unable to determine why the engine is running rough. Was it wrong of me to add Marvel Mystery Oil to my crankcase? Thank you in advance for the answers