i dont think so. i would imagine, it might be like mixing oils of different makes, they might start interferring with eachother in the crankcase, so at oil change, *** knows what woul come out of the oil pan. i use both, MMO recently now, and lucas UCL> in my opinion, the LUCAS outperforms the MMO. i would think, if both were mixed and used, the lucas ULC would was the MMO away, or jsut pas it throught the injectors for burning. plus you run the risk, of over lubing your upper cyclinders. i did that once with LUCAS UCL, made my pistons go so fast up and down, my car was slower moving. had to run tank to empty and refill, to flush it out.