Try some 'aluminium brightner' (order online from a valeting supplier)

Apply with a paint brush and spray / rinse off

Get great results by removing the IC and spraying off with pressure washer, (careful with the fins though or you'll be straightening them up for a while) you can also use some brake cleaner to give the inside a clean out too, whilst its off

Not that you would use it on your wheels but, 'wonder wheels' does a good job