My son was helping clean up the garage and decided to combine some half
empty containers of oil. He mixed a small amount of SAE 30 HD into a
larger container of SAE 30. Probably less than 25% HD.

The only thing I use SAE 30 for is my lawnmower. A little SAE 30 HD
mixed with the SAE 30 isn't going to make any difference is it?

Thanks.