What happen if you put the wrong oil grade into your car?

Wrong grade? What grade are you talking about? 5w30, 10w30, 50?

I changed oil for several years, and I can tell you that it is not a big deal. I imagine your car calls for a 5w30, but a 5w20 or 10w30 is not going to hurt anything. You want a thinner oil (smaller #'s) when it's cold out. If you have anything higher than a 10w30 in just drain it.