1. This car is not going to see a lot of rain/exposure to electrolytes 2. The fasteners are a 400 series SS so not as far away in potential as Grade 8 SS fasteners 3. The more noble metal is small in size compared to the less noble metal, further mitigating corrosive effects. This is why the aircraft industry can get away with SS fasteners in al structures.
The zinc fasteners, while closer in potential to aluminum, are less noble and when surrounded by the larger mass of al are a little more prone to corrosion than otherwise. The main reason that I switched to SS, with some caution, is that a few of the zinc fasteners rusted in only six months of sitting in a completely dry, never filled engine.
I didn't spend a boat load of money on those pulleys to see them attached by rusty bolts so you can believe that I'll keep a close eye on the SS fasteners. So far with coolant in the engine for over 18 months, there have been no visible problems.
