Wrong grade of oil for 2013 Chevrolet Volt?

What are the problems that might arise from using the wrong grade of oil. I have used 10-30 instead of10-40 though the 10-30 is synthetic.

The owners manual states to use Dexos specification 5W30.

10W30 and 10W40 are not recommended but probably would not result in problems during the first 100,000 miles.