When Oracle purges AWR data based on the retention policy, does it generate lots of redo?

I'm trying to clean up old AWR data.  We have 708 days worth, and the retention is set at 8.  I used alter session set "_swrf_test_action" = 72 to split the partitions, and new snaps are being created in the new partitions.   But then I thought I'd also drop some of the old snaps, and that ended up causing problems with the amount of redo being generated.  So I was thinking I'd leave it alone and let the Oracle cleanup process handle it.  Can it truncate the partitions?   However, if it's going to do deletes and generate lots of redo,