Well I have chimed in on this topic with all of my attempts and findings over the last several years. However, I have something new to add.

Last spring I installed the correct fan and at the same time added one bottle of Royal Purple's version of Water Wetter. Up until this past week I have been giving all the credit to installing the correct fan. HOWEVER, last week we pulled my motor to change the rope seal to the new BOP rear main seal. In doing so I lost my additive in the radiator.

Mind you I have been driving ALL SUMMER down here in FL and have not ran hot once since the new fan and additive. Now that I refilled the radiator and DID NOT put the additive back in, I ran warm again this past Saturday when we went to Old Town cruise.

Bottom line for me, I am now a beleiver in the radiator additives...