No, it will not cause any problems. The only thing is that whatever benefit you had gained by using a synthetic oil will quickly be lost when you go to a conventional oil. You will loose the superior protection synthetics can provide and you will save a bit of money--maybe. If you wish to convert back to a conventional oil you can do it at your next oil change. Further, I know for a fact, Mobil 1 can be mixed with conventional oils with no problem at all. They have a Tech Line to answer such questions. Feel free to use a dino oil. I do not think it is a good idea as a general rule to mix oils are switch wildly around seeking the cheapest oil on sale at Wally World. J