It might not hurt if it were 1 quart of the 20W-50 per fill (20-25%), but I wouldn't go much more than that - aviation oil is different from passenger car oil.
Might want to try and sell it to someone who can use it, and buy auto oil with the money......
Aviation oil is "ashless dispersant" which means its additive content is minimal, almost non-detergent oil. There is no ZDDP, but a few of them have TCP to prevent cam and lifter wear. I used Aeroshell in a BMW motorcycle for a few thousand miles. There were some varnish deposits, but no other problems. I would try and sell it. If not, as the post above, use only one quart per oil change in your cars, maybe mixed with 5W-20.
