If I was you, this is what you could do, just to use it up and not waste it. Mobil 1 is good oil. So why don't you just slowly. Its not going to hurt your car at all to put 1 quart of the 15w-50 stuff in with 4 quarts of the 5-30 oil. And you can use it for top off and stuff. If anything, a little extra viscosity will be good for your car if it has higher mileage.